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Esta memoria constituye el resumen de actividades de la red INTERMAT IX (red de investigación INTERdisciplinar en MATeriales). En su novena edición, la red INTERMAT se ha focalizado en desarrollar dos experiencias educativas con los estudiantes de la asignatura “Sólidos Inorgánicos” del Grado en Química. Por un lado, se han desarrollado con profundidad conceptos relativos a las tipologías de enlace atómico, así como a la dimensión (tamaño) de los iones de especies químicas, que determinan las estructuras cristalinas de los sólidos inorgánicos y sus propiedades, mediante la utilización de herramientas TIC y de impresión 3D. La utilización de dichas herramientas ha permitido mejorar sustancialmente el proceso de enseñanza-aprendizaje de los estudiantes, quienes manifestaron después de la experiencia profundos conocimientos del enlace atómico. Por otro lado, y de forma complementaria, se ha trabajado también en la integración del formato de presentaciones PechaKucha en una metodología docente de aprendizaje basado en proyectos (ABP). Con esta experiencia se ha conseguido mejorar la organización de tiempos y espacios durante el proceso de enseñanza-aprendizaje, el modo y el canal en el que se suministra la información, así como la orientación y gestión de las actividades de aprendizaje y las relaciones interpersonales.

Two-dimensional (2D) massive Dirac electrons possess a finite Berry curvature, with Chern number $\pm 1/2$, that entails both a quantized dc Hall response and a subgap full-quarter Kerr rotation. The observation of these effects in 2D massive Dirac materials such as gapped graphene, hexagonal boron nitride or transition metal dichalcogenides (TMDs) is obscured by the fact that Dirac cones come in pairs with opposite sign Berry curvatures, leading to a vanishing Chern number. Here, we show that the presence of spin-orbit interactions, combined with an exchange spin splitting induced either by diluted magnetic impurities or by proximity to a ferromagnetic insulator, gives origin to a net magneto-optical Kerr effect in such systems. We focus on the case of TMD monolayers and study the dependence of Kerr rotation on frequency and exchange spin splitting. The role of the substrate is included in the theory and found to critically affect the results. Our calculations indicate that state-of-the-art magneto-optical Kerr spectroscopy can detect a single magnetic impurity in diluted magnetic TMDs., 8 pages, 3 figures

As the first of a series of molecular solenoids, two classes of dithia[7]helicenes (coil-shaped molecules with sulfur atoms integrated within a helical conjugated system) have been devised and synthesized to be used in molecular electronics. We used a modular assembly of fragments using Pd catalyzed coupling reactions and a final photocyclization step for the syntheses; this strategy gave us straightforward access to helicenes bearing thiophene end rings with either exo or endo topologies. Unequivocal structural characterization was carried out by X-ray crystallography. In the solid state, their crystal architectures show little similarities; both can be considered an ensemble of heterochiral dimers (P/M) that are themselves very different in nature in light of their main pairing interactions. On a gold surface, the effect of the sulfur atom is to strengthen their binding to the electrodes, as manifested by scanning tunneling microscopy (STM) performed at room temperature. Different coating patterns were observed for each class of molecule, although the most prominent finding is that we could see resolved STM images of a single molecule, with a full display of its inherent chirality under room temperature conditions. Financial support by the Spanish Ministry of Economy and Competitiveness (MAT2016-78625-C2-1-P and MAT2016-78625-C2-2-P), the Generalitat Valenciana (PROMETEO/2017/139 and CDEIGENT/2018/028), and finally the University of Alicante (VIGROB-285 and 188) is gratefully acknowledged.

Efficient and versatile spin-to-charge current conversion is crucial for the development of spintronic applications, which strongly rely on the ability to electrically generate and detect spin currents. In this context, the spin Hall effect has been widely studied in heavy metals with strong spin-orbit coupling. While the high crystal symmetry in these materials limits the conversion to the orthogonal configuration, unusual configurations are expected in low symmetry transition metal dichalcogenide semimetals, which could add flexibility to the electrical injection and detection of pure spin currents. Here, we report the observation of spin-to-charge conversion in MoTe$_2$ flakes, which are stacked in graphene lateral spin valves. We detect two distinct contributions arising from the conversion of two different spin orientations. In addition to the conventional conversion where the spin polarization is orthogonal to the charge current, we also detect a conversion where the spin polarization and the charge current are parallel. Both contributions, which could arise either from bulk spin Hall effect or surface Edelstein effect, show large efficiencies comparable to the best spin Hall metals and topological insulators. Our finding enables the simultaneous conversion of spin currents with any in-plane spin polarization in one single experimental configuration., 14 pages, 4 figures, and Supporting Information

Shrinking spintronic devices to the nanoscale ultimately requires localized control of individual atomic magnetic moments. At these length scales, the exchange interaction plays important roles, such as in the stabilization of spin-quantization axes, the production of spin frustration, and creation of magnetic ordering. Here, we demonstrate the precise control of the exchange bias experienced by a single atom on a surface, covering an energy range of 4 orders of magnitude. The exchange interaction is continuously tunable from milli-eV to micro-eV by adjusting the separation between a spin-1/2 atom on a surface and the magnetic tip of a scanning tunneling microscope. We seamlessly combine inelastic electron tunneling spectroscopy and electron spin resonance to map out the different energy scales. This control of exchange bias over a wide span of energies provides versatile control of spin states, with applications ranging from precise tuning of quantum state properties, to strong exchange bias for local spin doping. In addition, we show that a time-varying exchange interaction generates a localized ac magnetic field that resonantly drives the surface spin. The static and dynamic control of the exchange interaction at the atomic scale provides a new tool to tune the quantum states of coupled-spin systems. Fil: Yang, Kai. Ibm Research; Estados Unidos Fil: Paul, William. Ibm Research; Estados Unidos Fil: Natterer, Fabian D.. Ibm Research; Estados Unidos. Universitat Zurich; Suiza Fil: Lado, Jose Luis. Eidgenössische Technische Hochschule; Suiza Fil: Bae, Yujeong. Ewha Womans University; Corea del Sur. Ibm Research; Estados Unidos Fil: Willke, Philip. Ibm Research; Estados Unidos. Institute for Basic Science; Corea del Sur Fil: Choi, Taeyoung. Institute for Basic Science; Corea del Sur. Ewha Womans University; Corea del Sur Fil: Ferrón, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; Argentina Fil: Fernandez Rossier, Joaquín. Universidad de Alicante; España. International Iberian Nanotechnology Laboratory; Portugal Fil: Heinrich, Andreas. Institute for Basic Science; Corea del Sur. Ewha Womans University; Corea del Sur Fil: Lutz, Christopher. Ibm Research; Estados Unidos

El presente documento constituye la memoria final de la red INTERMAT VIII (red de investigación INTERdisciplinar en MATeriales). En esta 8ª edición de la red INTERMAT los integrantes han continuado centrando sus esfuerzos en experiencias docentes que han puesto en práctica los principios fundamentales de la Neurodidáctica. En concreto, el trabajo se ha focalizado en el desarrollo de nuevas metodologías docentes basadas en Neurodidáctica y cronopedagogía para la mejora de los procesos de ordenamiento mental durante el aprendizaje. Más en particular, se han desarrollado los siguientes aspectos: i) estudio de la variación del ritmo cardíaco y su influencia en el proceso de aprendizaje en estudiantes universitarios; ii) utilización de herramientas de gestión online para estudios de tercer ciclo en ciencias experimentales (concepto de universidad sin muros); y iii) entornos de colaboración forzada en docencia universitaria: metodologías diseñadas en paralelismo a experimentos realizados con grandes simios.

The object kinetic Monte Carlo (OKMC) method has proven to be an excellent tool to better understand microstructure evolution in irradiated materials, from metals to semiconductors. Its most valuable capability is that it provides a way to connect parameters obtained from fundamental models, such as first principles calculations, to experimental observations by expanding simulated time and length scales. However, the OKMC method has many limitations that pose questions on its predictive capabilities and an important effort is taking place to improve the model. In this review, first we describe the object kinetic Monte Carlo methodology, then a few examples are presented in the field of radiation damage of metals and the limitations of the method and its applicability discussed. To conclude, an outlook on the future of this computational model is given. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 under grant agreement No 633053. The research leading to these results is partly funded by the European Atomic Energy Community’s (Euratom) H2020 WP 2016-2017 call NFRP13 (M4F) and in the framework of the EERA (European Energy Research Alliance) Joint Programme on Nuclear Materials.

A variety of planar π-conjugated hydrocarbons such as heptauthrene, Clar’s goblet and, recently synthesized, triangulene have two electrons occupying two degenerate molecular orbitals. The resulting spin of the interacting ground state is often correctly anticipated as S = 1, extending the application of Hund’s rules to these systems, but this is not correct in some instances. Here we provide a set of rules to correctly predict the existence of zero mode states as well as the spin multiplicity of both the ground state and the low-lying excited states, together with their open- or closed-shell nature. This is accomplished using a combination of analytical arguments and configuration interaction calculations with a Hubbard model, both backed by quantum chemistry methods with a larger Gaussian basis set. Our results go beyond the well established Lieb’s theorem and Ovchinnikov’s rule, as we address the multiplicity and the open-/closed-shell nature of both ground and excited states. J.F.-R. and R.O. acknowledge financial support from MINECO-Spain (grant no. MAT2016-78625-C2) and from the Portuguese “Fundação para a Ciência e a Tecnologia” (FCT) for the project P2020-PTDC/FIS-NAN/4662/2014. J.F.-R., M.M.-F. and N.G.-M. acknowledge support from the P2020-PTDC/FISNAN/3668/2014. J.F.-R. acknowledges support from UTAPEXPL/NTec/0046/2017 projects as well as Generalitat Valenciana funding (Prometeo2017/139). R.O. and J.C.S.-G. acknowledge ACIF/2018/175 (Generalitat Valenciana and Fondo Social Europeo). M.M.-F. and R.B. acknowledge the Portuguese “Fundação para a Ciência e a Tecnologia” (FCT) for the project IF/00894/2015 and FCT ref. UID/CTM/50011/2019 for CICECO - Aveiro Institute of Materials. This project received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 664878.

The question of how loops nucleate and grow in α-Fe under irradiation is addressed using object kinetic Monte Carlo with parameters from molecular dynamics and density functional theory calculations. Two models are considered for the formation of loops, both based on recent atomistic simulations. In one model loops are formed by the interaction between ½ loops. In a second model small interstitial clusters, nucleated in the collision cascade, can grow as or ½ loops. Comparing results from the calculations to experimental measurements of loop densities, ratios and sizes produced by Fe+ 100 keV irradiation of UHP Fe thin films at room temperature, the validity of the models is assessed. For these experimental conditions, the reaction model does not seem to be very efficient in the production of loops due to the fast recombination of ½ loops to surfaces. Therefore, in our thin film simulations (at very low carbon concentrations) most loops are a result of the nucleation model. In bulk simulations this effect could change since the probability of interactions between ½ loops would increase. Moreover, simulations show that total visible cluster concentration depends strongly on sample thickness and carbon content, while crystal orientation does not seem to have a significant role. Finally, the ratio of to ½ visible clusters changes with increased carbon concentration. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The research leading to these results is partly funded by the European Atomic Energy Communitys (Euratom) Seventh Framework Programme FP7/2007e2013 under grant agreement No. 604862 (MatISSE project) and in the framework of the EERA (European Energy Research Alliance) Joint Programme on Nuclear Materials.

[EN] The report of the Meissner effect in annealed samples of K3Tp (Tp = p-terphenyl) above 120 K has raised the interest in this deceptively simple material concerning superconductivity. We have investigated the structural integrity of the Tp framework in the annealed samples of KxTp at increasing processing time and temperature T. Our experimental studies show that both K2Tp and K3Tp mixing stoichiometries have identical Raman (solid state) and UV–vis (1,2-dimethoxyethane solution) spectra, being consistent with the molecular dianion by density functional theory and time-dependent density functional theory simulations. Magnetization vs T plots show no signs of superconductivity and neither do conductance vs T plots. Searching for potentially active minor byproducts formed during thermal processing, the role of K-doped poly(p-phenylene) has been examined, but it does not seem to explain the reported effects either. Further efforts are needed to explain the nature of this elusive phenomenon., Financial support by the Spanish Ministry of Economy and Competitiveness (FIS2015-64222-C2-1-P, MAT2014-52405-C2-2-R, and MAT2016-78625-C2-1-2-P), the Generalitat Valenciana (Grant PROMETEO/2017/139), and the University of Alicante (VIGROB-285) is gratefully acknowledged. M.C. thanks the VIDI of the University of Alicante for a predoctoral grant. A.G. greatly appreciates the computational resources provided by the Department of Applied Physics of the University of Alicante.

We consider a hybrid structure formed by graphene and an insulating antiferromagnet, separated by a dielectric of thickness up to $d\simeq 500 \,nm$. When uncoupled, both graphene and the antiferromagnetic surface host their own polariton modes coupling the electromagnetic field with plasmons in the case of graphene, and with magnons in the case of the antiferromagnet. We show that the hybrid structure can host two new types of hybrid polariton modes. First, a surface magnon-plasmon polariton whose dispersion is radically changed by the carrier density of the graphene layer, including a change of sign in the group velocity. Second, a surface plasmon-magnon polariton formed as a linear superposition of graphene surface plasmon and the antiferromagnetic bare magnon. This polariton has a dispersion with two branches, formed by the anticrossing between the dispersive surface plasmon and the magnon. We discuss the potential these new modes have for combining photons, magnons, and plasmons to reach new functionalities., Comment: 12 pages, 4 figures

We propose a method to realize a broad class of tunable fermionic Hamiltonians in graphene bilayer. For that matter, we consider graphene bilayer functionalized with sp3 defects that induce zero-energy resonances hosting an individual electron each. The application of an off-plane electric field opens up a gap, so that the zero-energy resonance becomes an in-gap bound state whose confinement scales inversely with the gap. Controlling both the distance among the defects and the applied electric field, we can define fermionic models, even lattices, whose hoppings and Coulomb interactions can be tuned. We consider in detail the case of triangular and honeycomb artificial lattices and we show how, for a given arrangement of the sp3 centers, these lattices can undergo an electrically controlled transition between the weak and strong coupling regimes. We acknowledge Grant No. P2020-PTDC/FIS-NAN/3668/2014, financial support Generalitat Valenciana funding Prometeo2017/139 and MINECO Spain (Grant No. MAT2016-78625-C2).

We study the optical properties of semiconducting transition metal dichalcogenide monolayers under the influence of strong out-of-plane magnetic fields, using the effective massive Dirac model. We pay attention to the role of spin-orbit-coupling effects, doping level, and electron-electron interactions, treated at the Hartree-Fock level. We find that optically induced valley and spin imbalance, commonly attained with circularly polarized light, can also be obtained with linearly polarized light in the doped regime. Additionally, we explore an exchange-driven mechanism to enhance the spin-orbit splitting of the conduction band, in n -doped systems, controlling both the carrier density and the intensity of the applied magnetic field., We thank A. J. Chaves and L. Brey for fruitful discussions. G.C. thanks Departamento de Fisica Aplicada at Universidad de Alicante for their hospitality. G.C. and J.F.-R. acknowledge financial support from Fundacao para a Ciencia e a Tecnologia (FCT) for the Grant No. P2020-PTDC/FIS-NAN/4662/2014. J.H. acknowledges financial support by the QUSCOPE Center, sponsored by the Villum foundation. J.F.-R. acknowledges financial support from FCT for the Grants No. P2020-PTDC/FIS-NAN/3668/2014 and No. UTAP-EXPL/NTec/0046/2017, as well as Generalitat Valenciana funding Prometeo2017/139 and MINECO-Spain (Grant No. MAT2016-78625-C2). N.M.R.P. acknowledges financial support from the European Commission through the project "Graphene-Driven Revolutions in ICT and Beyond" (Ref. No. 785219) and the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Financing Grant No. UID/FIS/04650/2013. Additionally, N.M.R.P. acknowledges COMPETE2020, PORTUGAL2020, FEDER and the Portuguese Foundation for Science and Technology (FCT) for the Grants No. PTDC/FIS-NAN/3668/2013 and No. POCI-01-0145-FEDER-028114., info:eu-repo/semantics/publishedVersion

Nuclear spins serve as sensitive probes in chemistry1 and materials science2 and are promising candidates for quantum information processing3–6. NMR, the resonant control of nuclear spins, is a powerful tool for probing local magnetic environments in condensed matter systems, which range from magnetic ordering in high-temperature superconductors7,8 and spin liquids9 to quantum magnetism in nanomagnets10,11. Increasing the sensitivity of NMR to the single-atom scale is challenging as it requires a strong polarization of nuclear spins, well in excess of the low polarizations obtained at thermal equilibrium, as well as driving and detecting them individually4,5,12. Strong nuclear spin polarization, known as hyperpolarization, can be achieved through hyperfine coupling with electron spins2. The fundamental mechanism is the conservation of angular momentum: an electron spin flips and a nuclear spin flops. The nuclear hyperpolarization enables applications such as in vivo magnetic resonance imaging using nanoparticles13, and is harnessed for spin-based quantum information processing in quantum dots14 and doped silicon15–17. Here we polarize the nuclear spins of individual copper atoms on a surface using a spin-polarized current in a scanning tunnelling microscope. By employing the electron–nuclear flip-flop hyperfine interaction, the spin angular momentum is transferred from tunnelling electrons to the nucleus of individual Cu atoms. The direction and magnitude of the nuclear polarization is controlled by the direction and amplitude of the current. The nuclear polarization permits the detection of the NMR of individual Cu atoms, which is used to sense the local magnetic environment of the Cu electron spin. Fil: Yang, Kai. Ibm Research; Estados Unidos Fil: Willke, Philip. Ibm Research; Estados Unidos. Institute for Basic Science. Center for Quantum Nanoscience; Corea del Sur. Ewha Womans University; Corea del Sur Fil: Bae, Yujeong. Ibm Research; Estados Unidos. Institute for Basic Science. Center for Quantum Nanoscience; Corea del Sur. Ewha Womans University; Corea del Sur Fil: Ferrón, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de Física; Argentina Fil: Lado, Jose Luis. Universitat Zurich; Suiza. International Iberian Nanotechnology Laboratory; Portugal Fil: Ardavan, Arzhang. University of Oxford; Reino Unido Fil: Fernandez Rossier, Joaquín. Universidad de Alicante; España. International Iberian Nanotechnology Laboratory; Portugal Fil: Heinrich, Andreas. Institute for Basic Science. Center for Quantum Nanoscience; Corea del Sur. Ewha Womans University; Corea del Sur Fil: Lutz, Christopher. Ibm Research; Estados Unidos

The mechanically controllable break junction (MCBJ) experimental setup is one of the main techniques employed in the study of electronic transport properties at the atomic and molecular scales. This work presents the construction of an inexpensive and simple but robust setup that shows the emergence of conductance quantization as a macroscopic gold wire is pulled to atomic dimensions. The homemade device is based on the MCBJ principle and allows repeatedly forming and breaking the metallic contact to perform a statistical analysis of the data extracting the most frequent electron transport structure. The histogram built from conductance measurements, at room temperature in air, show that the quality of the MCBJ equipment developed here is comparable to that of more sophisticated devices used in research laboratories. It is able to resolve up to three conductance peaks associated with gold nanowires reported in the literature. Such an experiment is suggested to be implemented as a powerful pedagogical tool in modern undergraduate physics labs. We are grateful for all the support of Generalitat Valenciana through PROMETEO2017/139 and GENT (CDEIGENT2018/028). This work was supported by the CEPRA Grant XII-2018-06 ‘Mechanical Spectroscopy’.

Magnons dominate the magnetic response of the recently discovered insulating ferromagnetic two dimensional crystals such as CrI$_3$. Because of the arrangement of the Cr spins in a honeycomb lattice, magnons in CrI$_3$ bear a strong resemblance with electronic quasiparticles in graphene. Neutron scattering experiments carried out in bulk CrI$_3$ show the existence of a gap at the Dirac points, that has been conjectured to have a topological nature. Here we propose a theory for magnons in ferromagnetic CrI$_3$ monolayers based on an itinerant fermion picture, with a Hamiltonian derived from first principles. We obtain the magnon dispersion for 2D CrI$_3$ with a gap at the Dirac points with the same Berry curvature in both valleys. For CrI$_3$ ribbons, we find chiral in-gap edge states. Analysis of the magnon wave functions in momentum space further confirms their topological nature. Importantly, our approach does not require to define a spin Hamiltonian, and can be applied to both insulating and conducting 2D materials with any type of magnetic order., Includes supplementary material

Taking advantage of nuclear spins for electronic structure analysis, magnetic resonance imaging, and quantum devices hinges on knowledge and control of the surrounding atomic-scale environment. We measured and manipulated the hyperfine interaction of individual iron and titanium atoms placed on a magnesium oxide surface by using spin-polarized scanning tunneling microscopy in combination with single-atom electron spin resonance. Using atom manipulation to move single atoms, we found that the hyperfine interaction strongly depended on the binding configuration of the atom. We could extract atom- and position-dependent information about the electronic ground state, the state mixing with neighboring atoms, and properties of the nuclear spin. Thus, the hyperfine spectrum becomes a powerful probe of the chemical environment of individual atoms and nanostructures. Fil: Willke, Philip. Ewha Womans University; Corea del Norte. IBM Almaden Research Center; Estados Unidos. Institute for Basic Science; Corea del Norte Fil: Bae, Yujeong. Ewha Womans University; Estados Unidos. Institute for Basic Science; Corea del Norte. IBM Almaden Research Center; Estados Unidos Fil: Yang, Kai. IBM Almaden Research Center; Estados Unidos Fil: Lado, Jose Luis. International Iberian Nanotechnology Laboratory; Portugal. Universitat Zurich; Suiza Fil: Ferrón, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de Física; Argentina Fil: Choi, Taeyoung. Seoul National University; Corea del Sur. Ewha Womans University; Estados Unidos Fil: Ardavan, Arzhang. University of Oxford; Reino Unido Fil: Fernandez Rossier, Joaquín. International Iberian Nanotechnology Laboratory; Portugal Fil: Heinrich, Andreas. Seoul National University; Corea del Sur. Ewha Womans University; Estados Unidos Fil: Lutz, Christopher. IBM Almaden Research Center; Estados Unidos

A scanning tunneling microscope is used to explore the evolution of electron and Cooper-pair transport across single Mn-phthalocyanine molecules adsorbed on Pb(111) from tunneling to contact ranges. Normal-metal as well as superconducting tips give rise to a gradual transition of the Bardeen-Cooper-Schrieffer energy gap in the tunneling range into a zero-energy resonance close to and at contact. Supporting transport calculations show that in the normal-metal–superconductor junctions this resonance reflects the merging of in-gap Yu-Shiba-Rusinov states as well as the onset of Andreev reflection. For the superconductor-superconductor contacts, the zero-energy resonance is rationalized in terms of a finite Josephson current that is carried by phase-dependent Andreev and Yu-Shiba-Rusinov levels. Financial support by the Deutsche Forschungsgemeinschaft through Grant No. KR 2912/10-1, the FCT (Projects No. PTDC/FIS-NAN/4662/2014 and No. P2020-PTDC/FISNAN/3668/2014), and the MINECO-Spain (MAT2016-78625-C2) is acknowledged. J.L.L. acknowledges financial support from the ETH Zurich Postdoctoral Fellowship program.

Magnetic insulators are a key resource for next-generation spintronic and topological devices. The family of layered metal halides promises varied magnetic states, including ultrathin insulating multiferroics, spin liquids, and ferromagnets, but device-oriented characterization methods are needed to unlock their potential. Here, we report tunneling through the layered magnetic insulator CrI₃ as a function of temperature and applied magnetic field.We electrically detect the magnetic ground state and interlayer coupling and observe a fieldinducedmetamagnetic transition.The metamagnetic transition results in magnetoresistances of 95, 300, and 550% for bilayer, trilayer, and tetralayer CrI₃ barriers, respectively.We further measure inelastic tunneling spectra for our junctions, unveiling a rich spectrum consistent with collective magnetic excitations (magnons) in CrI₃., Gordon and Betty Moore Foundation (Grant GBMF4541)

We propose spin valves where a 2D non-magnetic conductor is intercalated between two ferromagnetic insulating layers. In this setup, the relative orientation of the magnetizations of the insulating layers can have a strong impact on the in-plane conductivity of the 2D conductor. We first show this for a graphene bilayer, described with a tight-binding model, placed between two ferromagnetic insulators. In the anti-parallel configuration, a band gap opens at the Dirac point, whereas in the parallel configuration, the graphene bilayer remains conducting. We then compute the electronic structure of graphene bilayer placed between two monolayers of the ferromagnetic insulator CrI$_3$, using density functional theory. Consistent with the model, we find that a gap opens at the Dirac point only in the antiparallel configuration., 5 pages, 4 figures

Topological invariants allow to characterize Hamiltonians, predicting the existence of topologically protected in-gap modes. Those invariants can be computed by tracing the evolution of the occupied wavefunctions under twisted boundary conditions. However, those procedures do not allow to calculate a topological invariant by evaluating the system locally, and thus require information about the wavefunctions in the whole system. Here we show that artificial neural networks can be trained to identify the topological order by evaluating a local projection of the density matrix. We demonstrate this for two different models, a 1-D topological superconductor and a 2-D quantum anomalous Hall state, both with spatially modulated parameters. Our neural network correctly identifies the different topological domains in real space, predicting the location of in-gap states. By combining a neural network with a calculation of the electronic states that uses the Kernel Polynomial Method, we show that the local evaluation of the invariant can be carried out by evaluating a local quantity, in particular for systems without translational symmetry consisting of tens of thousands of atoms. Our results show that supervised learning is an efficient methodology to characterize the local topology of a system., Comment: 9 pages, 6 figures

La adaptación de la transmisión del conocimiento por parte del profesorado a nuevas situaciones, como puede ser la gestión de las emociones de los alumnos según un modelo motivador de enseñanza, permite que se planteen cuestiones sobre el continuo desarrollo de sus competencias. Por otro lado, existe una carencia pedagógica y didáctica desde los inicios de la formación de los profesores, puesto que los planes de estudios no contemplan dicha carga conceptual en los programas de todas las áreas, sobre todo en las científicas. Como propuesta de mejora para los mencionados aspectos, se planteó la red de trabajo INTERMAT VII con los objetivos de desarrollar los siguientes aspectos: i) el estudio de la gamificación como una nueva alternativa pedagógica estratégica, que sirve como herramienta para los docentes que se enfrentan a nuevos desafíos, facilitando así una experiencia exitosa al profesorado dispuesto a aplicar los 12 principios de la neurodidáctica mediante la utilización de la gamificación ajedrecística; y ii) la posible adaptación del programa universitario de las titulaciones “Profesorado en Química” y “Grado en Química” impartidas por la Universidad Nacional de Rosario al sistema educativo universitario español, con el fin de suplir las dificultades presentes de formación del futuro docente de ciencias.

The ten articles [1–10] included in this Special Issue on “Liquid Metals” do not intend to comprehensively cover this extensive field, but, rather, to highlight recent discoveries that have greatly broadened the scope of technological applications of these materials. Improvements in understanding the physics of liquid metals are, to a large extent, due to the powerful theoretical tools in the hands of scientists, either semi-empirical [1,5,6] or ab initio (molecular dynamics, see [7]). Surface tension and wetting at metal/ceramic interfaces is an everlasting field of fundamental research with important technological implications. The review of [2] is broad enough, as the work carried out at Grenoble covers almost all interesting matters in the field. Some issues of interest in geophysics and astrophysics are discussed in [3]. The recently discovered liquid–liquid transition in several metals is dealt with in [4]. The fifth contribution [5] discusses the role of icosahedral superclusters in crystallization. In [6], thermodynamic calculations are carried out to identify the regions of the ternary phase diagram of Al-Cu-Y, where the formation of amorphous alloys is most probable. Experimental data and ab initio calculations are presented in [7] to show that an optimal microstructure is obtained if Mg is added to the Al-Si melt before than the modifier AlP alloy. Shock-induced melting of metals by means of laser driven compression is discussed in [8]. With respect to recent discoveries, one of the most outstanding developments is that of gallium alloys that are liquid at room temperature [9], and that, due to the oxide layer that readily cover their surface, maintain some “stiffness”. This has opened the possibility of 3D printing with liquid metals. The last article in this Special Issue [10] describes nano-liquid metals, a suspension of liquid metal and its alloy containing nanometer-sized particles. A room-temperature nano-liquid metal and its alloys were first introduced in the area of cooling high heat flux devices, which now is a commercial reality. However, their applications are not only in chip cooling, and can also be extended to waste heat recovery, kinetic energy harvesting, thermal interface material, etc. This is mainly due to properties such as low melting point, high thermal and electrical conductivity, as well as other additional physical or chemical properties. These articles are summarized in more detail hereafter [...]

The inelastic portion of the tunnel current through an individual magnetic atom grants unique access to read out and change the atom's spin state, but it also provides a path for spontaneous relaxation and decoherence. Controlled closure of the inelastic channel would allow for the latter to be switched off at will, paving the way to coherent spin manipulation in single atoms. Here we demonstrate complete closure of the inelastic channels for both spin and orbital transitions due to a controlled geometric modification of the atom's environment, using scanning tunnelling microscopy (STM). The observed suppression of the excitation signal, which occurs for Co atoms assembled into chain on a Cu$_2$N substrate, indicates a structural transition affecting the d$_z$$^2$ orbital, effectively cutting off the STM tip from the spin-flip cotunnelling path., Comment: 4 figures plus 4 supplementary figures

We present molecular dynamics simulations with empirical potentials to study the type of defects produced when irradiating graphene with low energy carbon ions (100 eV and 200 eV) and different dose rates. Simulations show the formation of very stable structures such as dimers, single chains of carbons and double chains of carbons. These structures are similar to those described in the literature, observed experimentally when irradiating graphene. For high doses or dose rates, the formation of nanopores is observed, similar to previous results by other authors for higher energies of the implanted ions. These simulations show how tunning the different parameters of irradiation conditions can be used to selectively create defects in graphene. This work is supported by the Generalitat Valenciana through grant reference PROMETEO2012/011 and the Spanish government through grant FIS2010-21883.

We propose a new universal mechanism that makes it possible to drive an individual atomic spin using a spin polarized scanning tunnel microscope (STM) with an oscillating electric signal. We show that the combination of the distance dependent exchange with the magnetic tip and the electrically driven mechanical oscillation of the surface spins permits to control their quantum state. Based on a combination of density functional theory and multiplet calculations, we show that the proposed mechanism is essential to account for the recently observed electrically driven paramagnetic spin resonance (ESR) of an individual Fe atom on a MgO/Ag(100) surface. Our findings set the foundation to deploy the ESR-STM quantum sensing technique to a much broader class of systems., Comment: 7 pages, 3 figures

Quantum spin networks having engineered geometries and interactions are eagerly pursued for quantum simulation and access to emergent quantum phenomena such as spin liquids. Spin-1/2 centers are particularly desirable, because they readily manifest coherent quantum fluctuations. Here we introduce a controllable spin-1/2 architecture consisting of titanium atoms on a magnesium oxide surface. We tailor the spin interactions by atomic-precision positioning using a scanning tunneling microscope (STM) and subsequently perform electron spin resonance on individual atoms to drive transitions into and out of quantum eigenstates of the coupled-spin system. Interactions between the atoms are mapped over a range of distances extending from highly anisotropic dipole coupling to strong exchange coupling. The local magnetic field of the magnetic STM tip serves to precisely tune the superposition states of a pair of spins. The precise control of the spin-spin interactions and ability to probe the states of the coupled-spin network by addressing individual spins will enable the exploration of quantum many-body systems based on networks of spin-1/2 atoms on surfaces. Fil: Yang, Kai. Ibm Research; Estados Unidos Fil: Bae, Yujeong. Ibm Research; Estados Unidos. Center for Quantum Nanoscience, Institute for Basic Science (IBS); Corea del Sur. Ewha Womans University; Corea del Sur Fil: Paul, William. Ibm Research; Estados Unidos Fil: Natterer, Fabian D.. Ibm Research; Estados Unidos. Ecole Polytechnique Federale de Lausanne; Suiza Fil: Willke, Philip. Ibm Research; Estados Unidos. Center for Quantum Nanoscience, Institute for Basic Science (IBS); Corea del Sur. Ewha Womans University; Corea del Sur Fil: Lado, Jose Luis. International Iberian Nanotechnology Laboratory; Portugal Fil: Ferrón, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; Argentina Fil: Choi, Taeyoung. Center for Quantum Nanoscience, Institute for Basic Science (IBS); Corea del Sur. Ewha Womans University; Corea del Sur Fil: Fernandez Rossier, Joaquín. International Iberian Nanotechnology Laboratory; Portugal. Universidad de Alicante; España Fil: Heinrich, Andreas J.. Center for Quantum Nanoscience, Institute for Basic Science (IBS); Corea del Sur. Ewha Womans University; Corea del Sur Fil: Lutz, Christopher P.. Ibm Research; Estados Unidos

Phase coherence of single-atom spins on surfaces is investigated in a scanning tunneling microscopy experiment., Spin resonance of individual spin centers allows applications ranging from quantum information technology to atomic-scale magnetometry. To protect the quantum properties of a spin, control over its local environment, including energy relaxation and decoherence processes, is crucial. However, in most existing architectures, the environment remains fixed by the crystal structure and electrical contacts. Recently, spin-polarized scanning tunneling microscopy (STM), in combination with electron spin resonance (ESR), allowed the study of single adatoms and inter-atomic coupling with an unprecedented combination of spatial and energy resolution. We elucidate and control the interplay of an Fe single spin with its atomic-scale environment by precisely tuning the phase coherence time T2 using the STM tip as a variable electrode. We find that the decoherence rate is the sum of two main contributions. The first scales linearly with tunnel current and shows that, on average, every tunneling electron causes one dephasing event. The second, effective even without current, arises from thermally activated spin-flip processes of tip spins. Understanding these interactions allows us to maximize T2 and improve the energy resolution. It also allows us to maximize the amplitude of the ESR signal, which supports measurements even at elevated temperatures as high as 4 K. Thus, ESR-STM allows control of quantum coherence in individual, electrically accessible spins.

Our analysis of the contact formation processes undergone by Au, Ag and Cu nanojunctions, reveals that the distance at which the two closest atoms on a pair of opposing electrodes jump into contact is, on average, two times longer for Au than either Ag or Cu. This suggests the existence of a longer range interaction between those two atoms in the case of Au, a result of the significant relativistic energy contributions to the electronic structure of this metal, as confirmed by ab initio calculations. Once in the contact regime, the differences between Au, Ag and Cu are subtle, and the conductance of single-atom contacts for metals of similar chemical valence is mostly determined by geometry and coordination., 4 pages, 4 figures

The development of communication channels at the ultimate size limit of atomic scale physical dimensions will make the use of quantum entities an imperative. In this regime, quantum fluctuations naturally become prominent and are generally considered to be detrimental. Here, we show that for spin-based information processing, these fluctuations can be uniquely exploited to gate the flow of classical binary information across a magnetic chain in thermal equilibrium. Moreover, this information flow can be controlled with a modest external magnetic field that drives the system through different many-body quantum phases in which the orientation of the final spin does or does not reflect the orientation of the initial input. Our results are general for a wide class of anisotropic spin chains that act as magnetic cellular automata and suggest that quantum phase transitions play a unique role in driving classical information flow at the atomic scale. L. B. and S. B. have received funding for this research from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC Grant agreement No. 308253 PACOMANEDIA; C. F. H. from the Leverhulme Trust (Grant No. RPG-2012-754) and EPSRC (Grant No. EP/M009564/1); J. F. R. from the UCLQ Visitors Program.

Graphite surfaces can be manipulated by several methods to create graphene structures of different shapes and sizes. Scanning tunneling microscopy (STM) can be used to create these structures either through mechanical contact between the tip and the surface or through electro-exfoliation. In the latter, the mechanisms involved in the process of exfoliation at an applied voltage are not fully understood. Here, we show how a graphite surface can be locally exfoliated in a systematic manner by applying an electrostatic force with a STM tip at the edge of a terrace, forming triangular flakes several nanometers in length. We demonstrate, through experiments and simulations, how these flakes are created by a two-step process: first a voltage ramp must be applied at the edge of the terrace, and then the tip must be scanned perpendicular to the edge. Ab initio electrostatic calculations reveal that the presence of charges on the graphite surface weakens the interaction between layers allowing for exfoliation at voltages in the same range as those used experimentally. Molecular dynamics simulations show that a force applied locally on the edge of a step produces triangular flakes such as those observed under STM. Our results provide new insights into surface modification that can be extended to other layered materials. Las superficies de grafito se pueden manipular mediante varios métodos para crear estructuras de grafeno de diferentes formas y tamaños. La microscopía de túnel de barrido (STM) se puede utilizar para crear estas estructuras ya sea a través del contacto mecánico entre la punta y la superficie o mediante electroexfoliación. En este último, los mecanismos involucrados en el proceso de exfoliación a un voltaje aplicado no se comprenden completamente. Aquí, mostramos cómo una superficie de grafito puede exfoliarse localmente de manera sistemática aplicando una fuerza electrostática con una punta STM en el borde de una terraza, formando escamas triangulares de varios nanómetros de longitud. Demostramos, a través de experimentos y simulaciones, cómo se crean estos copos mediante un proceso de dos pasos: primero se debe aplicar una rampa de voltaje en el borde de la terraza, y luego se debe escanear la punta perpendicular al borde. Los cálculos electrostáticos Ab initio revelan que la presencia de cargas en la superficie de grafito debilita la interacción entre capas, lo que permite la exfoliación a voltajes en el mismo rango que los utilizados experimentalmente. Las simulaciones de dinámica molecular muestran que una fuerza aplicada localmente en el borde de un escalón produce escamas triangulares como las observadas en STM. Nuestros resultados proporcionan nuevos conocimientos sobre la modificación de la superficie que pueden extenderse a otros materiales en capas. Universidad Nacional, Costa Rica Departamento de Física

We study a graphene Hall probe located on top of a magnetic surface as a detector of skyrmions, using as working principle the anomalous Hall effect produced by the exchange interaction of the graphene electrons with the non-coplanar magnetization of the skyrmion. We study the magnitude of the effect as a function of the exchange interaction, skyrmion size and device dimensions. Our calculations for multiterminal graphene nanodevices, working in the ballistic regime, indicate that for realistic exchange interactions a single skyrmion would give Hall voltages well within reach of the experimental state of the art. The proposed device could act as an electrical transducer that marks the presence of a single skyrmion in a nanoscale region, paving the way towards the integration of skyrmion-based spintronics and graphene electronics., 8 pages, 6 figures

Irradiation with low energy Ar ions of graphene membranes gives rise to changes in the mechanical properties of this material. These changes have been associated to the production of defects, mostly isolated vacancies. However, the initial state of the graphene membrane can also affect its mechanical response. Using molecular dynamics simulations we have studied defect production in graphene membranes irradiated with 140 eV Ar ions up to a dose of 0.075 × 1014 ions/cm2 and different initial strains, from −0.25% (compressive strain) to 0.25% (tensile strain). For all strains, the number of defects increases linearly with dose with a defect production of about 80% (80 defects every 100 ions). Defects are mostly single vacancies and di-vacancies, although some higher order clusters are also observed. Two different types of di-vacancies have been identified, the most common one being two vacancies at first nearest neighbours distance. Differences in the total number of defects with the applied strain are observed which is related to the production of a higher number of di-vacancies under compressive strain compared to tensile strain. We attribute this effect to the larger out-of-plane deformations of compressed samples that could favor the production of defects in closer proximity to others. Fil: Martinez Asencio, J.. Universidad de Alicante; España Fil: Ruestes, Carlos Javier. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Bringa, Eduardo Marcial. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Caturla, M. J.. Universidad de Alicante; España

Exchange interactions with itinerant electrons are known to act as a relaxation mechanism for individual local spins. The same exchange interactions induce the so-called RKKY indirect exchange interaction between two otherwise decoupled local spins. Here, we show that both the spin relaxation and the RKKY coupling can be seen as the dissipative and reactive response to the coupling of the local spins with the itinerant electrons. We thereby predict that the spin relaxation rates of magnetic nanostructures of exchanged coupled local spins, such as nanoengineered spin chains, have an oscillatory dependence on kFd, where kF is the Fermi wave number and d is the interspin distance, very much like the celebrated oscillations in the RKKY interaction. We demonstrate that both T1 and T2 can be enhanced or suppressed, compared to the single-spin limit, depending on the interplay between the Fermi surface and the nanostructure geometrical arrangement. Our results open a route to engineer spin relaxation and decoherence in atomically designed spin structures., J.F.R. acknowledges financial supported by MEC-Spain (Grant No. FIS2013-47328-C2-2-P) and Generalitat Valenciana (Grant No. ACOMP/2010/070), Prometeo. This work is funded by ERDF funds through the Portuguese Operational Program for Competitiveness and InternationalizationÐ COMPETE 2020, and National Funds through FCT-The Portuguese Foundation for Science and Technology, under the project PTDC/FIS-NAN/4662/2014 (Project. No. 016656). F.D. acknowledges support from Spanish Government through Grant No. MAT2015-66888-C3-2-R and Basque Government, Grant No. IT986-16.

We propose a mechanism to drive singlet-triplet spin transitions electrically in a wide class of graphene nanostructures that present pairs of in-gap zero modes, localized at opposite sublattices. Examples are rectangular nanographenes with short zigzag edges, armchair ribbon heterojunctions with topological in-gap states, and graphene islands with sp3 functionalization. The interplay between the hybridization of zero modes and the Coulomb repulsion leads to symmetric exchange interaction that favors a singlet ground state. Application of an off-plane electric field to the graphene nanostructure generates an additional Rashba spin-orbit coupling, which results in antisymmetric exchange interaction that mixes S=0 and S=1 manifolds. We show that modulation in time of either the off-plane electric field or the applied magnetic field permits performing electrically driven spin resonance in a system with very long spin-relaxation times. This work has been financially supported, in part, by FEDER funds. We acknowledge financial support from Marie-Curie-ITN Grant No. 607904-SPINOGRAPH, FCT, under the Projects No. PTDC/FIS-NAN/4662/2014 and No. PTDC/FISNAN/3668/2014, and MINECO-Spain (Grant No. MAT2016-78625-C2).

We review the problem of spin decoherence of magnetic atoms deposited on a surface. Recent breakthroughs in scanning tunnelling microscopy (STM) make it possible to probe the spin dynamics of individual atoms, either isolated or integrated in nanoengineered spin structures. Transport pump and probe techniques with spin polarized tips permit measuring the spin relaxation time T, while novel demonstration of electrically driven STM single spin resonance has provided a direct measurement of the spin coherence time T of an individual magnetic adatom. Here we address the problem of spin decoherence from the theoretical point of view. First we provide a short general overview of decoherence in open quantum systems and we discuss with some detail ambiguities that arise in the case of degenerate spectra, relevant for magnetic atoms. Second, we address the physical mechanisms that allows probing the spin coherence of magnetic atoms on surfaces. Third, we discuss the main spin decoherence mechanisms at work on a surface, most notably, Kondo interaction, but also spin–phonon coupling and dephasing by Johnson noise. Finally, we briefly discuss the implications in the broader context of quantum technologies., JFR acknowledges financial supported by MEC-Spain (FIS2013-47328-C2-2-P) and Generalitat Valenciana (ACOMP/2010/070), Prometeo. This work is funded by ERDF funds through the Portuguese Operational Program for Competitiveness and Internationalization COMPETE 2020, and National Funds through FCT – The Portuguese Foundation for Science and Technology, under the project “PTDC/FIS-NAN/4662/2014” (016656). FD acknowledges funding by the Ministerio de Economía y Competitividad (MINECO, Spain), with grant MAT2015-66888-C3-2-R., and Gobierno Vasco by grant IT986-16. We thank J. Sinova for financial support in the SPICE workshop on “Magnetic adatoms as building blocks for quantum magnetism”.

Two-dimensional semiconducting materials are particularly appealing for many applications. Although theory predicts a large number of two-dimensional materials, experimentally only a few of these materials have been identified and characterized comprehensively in the ultrathin limit. Lead iodide, which belongs to the transition metal halides family and has a direct bandgap in the visible spectrum, has been known for a long time and has been well characterized in its bulk form. Nevertheless, studies of this material in the nanometer thickness regime are rather scarce. In this article we demonstrate an easy way to synthesize ultrathin, highly crystalline flakes of PbI2 by precipitation from a solution in water. We thoroughly characterize the produced thin flakes with different techniques ranging from optical and Raman spectros-copy to temperature-dependent photoluminescence and electron microscopy. We compare the results to ab initio calculations of the band structure of the material. Finally, we fabricate photodetectors based on PbI2 and study their optoelectronic properties., main text 20 pages + 10 figures, supporting information 16 pages + 17 figures

We report on the fabrication, transport measurements, and density functional theory (DFT) calculations of atomic-size contacts made of gadolinium (Gd). Gd is known to have local moments mainly associated with f electrons. These coexist with itinerant s and d bands that account for its metallic character. Here we explore whether and how the local moments influence electronic transport properties at the atomic scale. Using both scanning tunneling microscope and lithographic mechanically controllable break junction techniques under cryogenic conditions, we study the conductance of Gd when only few atoms form the junction between bulk electrodes made of the very same material. Thousands of measurements show that Gd has an average lowest conductance, attributed to single-atom contact, below 2e2h. Our DFT calculations for monostrand chains anticipate that the f bands are fully spin polarized and insulating and that the conduction may be dominated by s, p, and d bands. We also analyze the electronic transport for model nanocontacts using the nonequilibrium Green's function formalism in combination with DFT. We obtain an overall good agreement with the experimental results for zero bias and show that the contribution to the electronic transport from the f channels is negligible and that from the d channels is marginal. B.O., C.S., J.F.R., J.J.P., and C.U. acknowledge financial support by MEC-Spain (Grant No. FIS2013-47328-C2 and MAT2016-78625-C2) and the Generalitat Valenciana under Grant No. PROMETEO/2012/011. C.S. and J.J.P. acknowledge the EU structural funds and the Comunidad de Madrid under NANOFRONTMAG-CM program Grant No. S2013/MIT-2850. J.L.L. and J.F.R. acknowledge Marie Curie ITN SPINOGRAPH FP7 under REA Grant Agreement No. 607904-13. B.O. acknowledges financial support by MEC Spain (Grant No. FIS2010-21883-C02-01) under brief stays abroad scholarship.

The interaction of electrons with a periodic potential of atoms in crystalline solids gives rise to band structure. The band structure of existing materials can be measured by photoemission spectroscopy and accurately understood in terms of the tight-binding model, however not many experimental approaches exist that allow to tailor artificial crystal lattices using a bottom-up approach. The ability to engineer and study atomically crafted designer materials by scanning tunnelling microscopy and spectroscopy (STM/STS) helps to understand the emergence of material properties. Here, we use atom manipulation of individual vacancies in a chlorine monolayer on Cu(100) to construct one- and two-dimensional structures of various densities and sizes. Local STS measurements reveal the emergence of quasiparticle bands, evidenced by standing Bloch waves, with tuneable dispersion. The experimental data are understood in terms of a tight-binding model combined with an additional broadening term that allows an estimation of the coupling to the underlying substrate., 7 figures, 12 pages, main text and supplementary material

Scattering of electrons by localized spins is the ultimate process enabling detection and control of the magnetic state of a spin-doped material. At the molecular scale, scattering is mediated by the orbitals hosting the spin. Here we report the selective excitation of a molecular spin by tunneling through different molecular orbitals. Spatially resolved tunneling spectra on iron-porphyrins reveal that the inelastic spin excitation extends beyond the iron site, changing shape and symmetry along the molecule. Combining density functional theory simulations with a phenomenological scattering model, we show that the extension and lineshape of the inelastic signal are due to excitation pathways assisted by different frontier orbitals. By selecting the intramolecular site for electron injection, the relative weight of iron and pyrrole orbitals in the tunneling process is modified. Thus, the excitation mechanism, reflected by its spectral lineshape, depends on the degree of localization and energy alignment of the chosen molecular orbital., This work has been funded by the COST 15128 Molecular Spintronics project, by Marie Curie IF ARTE, by the Spanish Ministerio de Economía y Competitividad (MINECO) through the cooperative grant No. MAT2016-78293 and grant No. FIS2016-75862-P, and by the Basque Government (Dep. Industry, Grant PI-2015-1-42, Dep. Education, Grant PI-2016-1-27 and Grant IT-756-13), the EU project PAMS (610446), and the European Regional Development Fund (ERDF).

El Espacio Europeo de Educación Superior exige, desde su complejo y ambicioso plan para favorecer el bienestar de sus ciudadanos a través de una enseñanza de máxima calidad, que se establezcan las garantías de calidad que marcan la Agencia Nacional de Evaluación de la Calidad y Acreditación (ANECA), la European Network for Quality Assurance in Higher Education (ENQA) y la International Network for Quality Assurance Agencies in Higher Education, Partiendo de estas exigencias, y teniendo en cuenta la emergencia de disciplinas en materia educativa relativamente nuevas, se exige al profesor universitario la materialización en el aula de nuevas metodologías que tengan en cuenta multitud de variables. Una de estas nuevas disciplinas, la neurodidáctica o neuroeducación, resulta especialmente interesante porque abarca campos como la psicología cognoscitiva, la neuropsicología, la filosofía, la didáctica y la neurología. El principal objetivo de la red INTERMAT VI ha sido revisar los principales avances desarrollados en neurodidáctica para favorecer la generación de sugerencias encaminadas a su empleo práctico en las aulas del contexto universitario.

La realització d’experiments de física utilitzant noves tecnologies és sovint més atractiva per als estudiants que els experiments convencionals. En aquest treball usem la targeta de so d’un ordinador per a mesurar el temps que transcorre entre dos sons. Hem portat a terme dos experiments per a calcular l’acceleració de la gravetat, on hem utilitzat la targeta de so de l’ordinador i el programa Audacity de gravació i edició de sons. El primer experiment es basa en la cinemàtica del tir parabòlic d’un cos, mentre que el segon experiment està basat en la llei d’inducció de Faraday quan un imant cau per un tub no metàl·lic on hi ha espires enrotllades. D’aquesta manera, hem obtingut l’acceleració de la gravetat mitjançant un procediment diferent a l’habitual en els laboratoris de física. També hem demostrat experimentalment que el temps de caiguda d’un cos no depèn de la seua velocitat horitzontal inicial ni de la seua massa, error molt comú entre els estudiants.

We revisit the problem of local moment formation in graphene due to chemisorption of individual atomic hydrogen or other analogous sp3 covalent functionalizations. We describe graphene with the single-orbital Hubbard model, so that the H chemisorption is equivalent to a vacancy in the honeycomb lattice. To circumvent artifacts related to periodic unit cells, we use either huge simulation cells of up to 8×105 sites, or an embedding scheme that allows the modeling of a single vacancy in an otherwise pristine infinite honeycomb lattice. We find three results that stress the anomalous nature of the magnetic moment (m) in this system. First, in the noninteracting (U=0) zero-temperature (T=0) case, the m(B) is a continuous smooth curve with divergent susceptibility, different from the stepwise constant function found for single unpaired spins in a gapped system. Second, for U=0 and T>0, the linear susceptibility follows a power law ∝T−α with an exponent of α=0.77 different from the conventional Curie law. For U>0, in the mean-field approximation, the integrated moment is smaller than m=1μB, in contrast with results using periodic unit cells. These three results highlight the fact that the magnetic response of the local moment induced by sp3 functionalizations in graphene is different from that of local moments in gapped systems, for which the magnetic moment is quantized and follows a Curie law, and from Pauli paramagnetism in conductors, for which linear susceptibility can be defined at T=0. The authors acknowledge financial support by Marie-Curie-ITN 607904-SPINOGRAPH. J.F.-R. acknowledges financial supported by MEC-Spain (GrantsNo. FIS2013-47328-C2-2-P and No. MAT2016-78625-C2) and Generalitat Valenciana (Grant No. ACOMP/2010/070), Prometeo, by European Regional Development Fund (ERDF) funds through the Portuguese Operational Program for Competitiveness and Internationalization COMPETE 2020, and National Funds through FCT, under the Project No. PTDC/FIS-NAN/4662/2014 (016656) [Portuguese Foundation for Science and Technology]. This work has been financially supported in part by FEDER funds.

Using molecular dynamics simulations with recent interatomic potentials developed for Fe, we have studied the defects in thin films of pure bcc Fe induced by the displacement cascade produced by Fe atoms of 50, 100, and 150 keV impinging under a channeling incident angle of 6° to a [001] direction. The thin films have a thickness between 40 and 100 nm, to reproduce the thickness of the samples used in transmission electron microscope in-situ measurements during irradiation. In the simulations we focus mostly on the effect of channeling and free surfaces on damage production. The results are compared to bulk cascades. The comparison shows that the primary damage in thin films of pure Fe is quite different from that originated in the volume of the material. The presence of near surfaces can lead to a variety of events that do not occur in bulk collisional cascades, such as the production of craters and the glide of self-interstitial defects to the surface. Additionally, in the range of energies and the incident angle used, channeling is a predominant effect that significantly reduces damage compared to bulk cascades. This work was supported by the FPVII projects FEMaS, GETMAT and PERFECT and by the MAT-IREMEV program of EFDA. We acknowledge the support of the European Commission, the European Atomic Energy Community (Euratom), the European Fusion Development Agreement (EFDA) and the Forschungszentrum Jülich GmbH, jointly funding the Project HPC for Fusion (HPC-FF), Contract number FU07-CT-2007-00055.

Odd- and even-layer variations in magnetization occur in two-dimensional chromium triiodide. Supported by Fundação para a Ciência e a Tecnologia grants P2020-PTDC/FIS-NAN/3668/2014 and UTAPEXPL/NTec/0046/2017.

We consider spin relaxation of finite-size spin chains exchanged coupled with a one dimensional (1D) electron gas at the edge of a Quantum Spin Hall (QSH) insulator. Spin lifetimes can be enhanced due to two independent mechanisms. First, the suppression of spin-flip forward scattering inherent in the spin momentum locking of the QSH edges. Second, the reduction of spin-flip backward scattering due to destructive interference of the quasiparticle exchange, modulated by $k_F d$, where $d$ is the inter-spin distance and $k_F$ is the Fermi wavenumber of the electron gas. We show that the spin lifetime of the $S=1/2$ ground state of odd-numbered chains of antiferromagnetically (AFM) coupled $S=1/2$ spins can be increased more than 4 orders of magnitude by properly tuning the product $k_Fd$ and the spin size $N$, in strong contrast with the 1D case. Possible physical realizations together with some potential issues are also discussed., 11 pages, 3 figures

Quantum spin tunneling (QST) and Kondo effect are two very different quantum phenomena that produce the same effect on quantized spins, namely, the quenching of their magnetization. However, the nature of this quenching is very different so that QST and Kondo effects compete with each other. Importantly, both QST and Kondo produce very characteristic features in the spectral function that can be measured by means of single spin scanning tunneling spectroscopy that makes it possible to probe the crossover from one regime to the other. We model this crossover, and the resulting changes in transport, using a non-perturbative treatment of a generalized Anderson model including magnetic anisotropy that leads to quantum spin tunneling. We predict that, at zero magnetic field, integer spins can feature a split-Kondo peak driven by quantum spin tunneling., 5 pages, 3 figures; accepted in EPJB; replaced with revised manuscript

The advent of devices based on single dopants, such as the single atom transistor, the single spin magnetometer and the single atom memory, motivates the quest for strategies that permit to control matter with atomic precision. Manipulation of individual atoms by means of low-temperature scanning tunnelling microscopy provides ways to store data in atoms, encoded either into their charge state, magnetization state or lattice position. A defining challenge at this stage is the controlled integration of these individual functional atoms into extended, scalable atomic circuits. Here we present a robust digital atomic scale memory of up to 1 kilobyte (8,000 bits) using an array of individual surface vacancies in a chlorine terminated Cu(100) surface. The memory can be read and rewritten automatically by means of atomic scale markers, and offers an areal density of 502 Terabits per square inch, outperforming state-of-the-art hard disk drives by three orders of magnitude. Furthermore, the chlorine vacancies are found to be stable at temperatures up to 77 K, offering prospects for expanding large-scale atomic assembly towards ambient conditions., 14 pages, 6 figures, incl. Supplementary Information

The conductance across an atomically narrow metallic contact can be measured by using scanning tunneling microscopy. In certain situations, a jump in the conductance is observed right at the point of contact between the tip and the surface, which is known as "jump to contact" (JC). Such behavior provides a way to explore, at a fundamental level, how bonding between metallic atoms occurs dynamically. This phenomenon depends not only on the type of metal but also on the geometry of the two electrodes. For example, while some authors always find JC when approaching two atomically sharp tips of Cu, others find that a smooth transition occurs when approaching a Cu tip to an adatom on a flat surface of Cu. In an attempt to show that all these results are consistent, we make use of atomistic simulations; in particular, classical molecular dynamics together with density functional theory transport calculations to explore a number of possible scenarios. Simulations are performed for two different materials: Cu and Au in a [100] crystal orientation and at a temperature of 4.2 K. These simulations allow us to study the contribution of short- and long-range interactions to the process of bonding between metallic atoms, as well as to compare directly with experimental measurements of conductance, giving a plausible explanation for the different experimental observations. Moreover, we show a correlation between the cohesive energy of the metal, its Young's modulus, and the frequency of occurrence of a jump to contact, W. Dednam thanks Dr. A. E. Botha for helpful discussions and acknowledges support from the National Research Foundation of South Africa through the Scarce Skills Masters scholarship funding programme (Grant Unique Number 92138). This work is supported by the Generalitat Valenciana through Grant Reference PROMETEO2012/011 and MINECO under Grant No. FIS2013-47328, by European Union structural funds and the Comunidad de Madrid Programs S2013/MIT-3007 and P2013/MIT-2850. This work is also part of the research programme of the Foundation for Fundamental Research on Matter (FOM), which is financially supported by the Netherlands Organisation for Scientific Research (NWO)

A clear demonstration of topological superconductivity (TS) and Majorana zero modes remains one of the major pending goals in the field of topological materials. One common strategy to generate TS is through the coupling of an s-wave superconductor to a helical half-metallic system. Numerous proposals for the latter have been put forward in the literature, most of them based on semiconductors or topological insulators with strong spin-orbit coupling. Here, we demonstrate an alternative approach for the creation of TS in graphene-superconductor junctions without the need for spin-orbit coupling. Our prediction stems from the helicity of graphene's zero-Landau-level edge states in the presence of interactions and from the possibility, experimentally demonstrated, of tuning their magnetic properties with in-plane magnetic fields. We show how canted antiferromagnetic ordering in the graphene bulk close to neutrality induces TS along the junction and gives rise to isolated, topologically protected Majorana bound states at either end.We also discuss possible strategies to detect their presence in graphene Josephson junctions through Fraunhofer pattern anomalies and Andreev spectroscopy. The latter, in particular, exhibits strong unambiguous signatures of the presence of the Majorana states in the form of universal zero-bias anomalies. Remarkable progress has recently been reported in the fabrication of the proposed type of junctions, which offers a promising outlook for Majorana physics in graphene systems., We acknowledge the support of the European Research Council (F. G.), the Spanish Ministry of Economy and Innovation through Grants No. FIS2011-23713 (F. G. and P. S.-J.) and No. FIS2012-33521 (R. A.), the Ramón y Cajal Programme (P. S.-J.), the Marie-Curie-ITN 607904-SPINOGRAPH (J. L., J. F. R., and F. G.), and Generalitat Valenciana (ACOMP/2010/070), Prometeo (J. F. R.)., https://doi.org/10.1103/PhysRevX.5.041042