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Magnons and plasmons are different collective modes, involving the spin and charge degrees of freedom, respectively. Formation of hybrid plasmon–magnon polaritons in heterostructures of plasmonic and magnetic systems faces two challenges, the small interaction of the electromagnetic field of the plasmon with the spins, and the energy mismatch, as in most systems plasmons have energies orders of magnitude larger than those of magnons. We show that graphene plasmons form polaritons with the magnons of two-dimensional ferromagnetic insulators, placed up to to half a micrometer apart, with Rabi splittings in the range of 100 GHz (dramatically larger than cavity magnonics). This is facilitated both by the small energy of graphene plasmons and the cooperative super-radiant nature of the plasmon–magnon coupling afforded by phase matching. We show that the coupling can be modulated both electrically and mechanically, and we propose a ferromagnetic resonance experiment implemented with a two-dimensional ferromagnet driven by graphene plasmons. We acknowledge financial support from the Fundação Para a Ciência e a Tecnologia, Portugal Grant No. PTDC/FIS-MAC/2045/2021) and from the European Union (Grant FUNLAYERS - 101079184). J.F.-R. and A.T.C. acknowledge financial support from the Swiss National Science Foundation Sinergia (Grant Pimag), MICIIN – Spain (Grant No. PID2019-109539GB-41), Generalitat Valenciana (Grant Nos. Prometeo2021/017 and MFA/2022/045), FEDER/Junta de Andalucía-Consejera de Transformación Económica, Industria, Conocimiento y Universidades (Grant No. P18-FR-4834). N.M.R.P. and M.I.V. acknowledge support by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/04650/2020, COMPETE 2020, PORTUGAL 2020, FEDER, and FCT through projects POCI-01-0145-FEDER-028114, POCI-01-0145-FEDER-02888 and PTDC/NANOPT/29265/2017, PTDC/FIS-MAC/2045/2021, and EXPL/FIS-MAC/0953/2021, and from the European Commission through the project Graphene Driven Revolutions in ICT and Beyond (Ref. No. 881603, CORE 3).

After evaporation of the organic solvents, benzene, toluene, and cyclohexane on gold substrates, Scanning Tunneling Microscope (STM) shows the presence of a remaining adsorbed layer. The different solvent molecules were individually observed at ambient conditions, and their electronic transport properties characterized through the STM in the Break Junction approach. The combination of both techniques reveals, on one hand, that solvents are not fully evaporated over the gold electrode and, secondly, characterize the electronic transport of the solvents in molecular electronics. This work was supported by the Spanish Government (MAT2016-78625-C2 and PID2019-109539 GB-C41) and the Generalitat Valenciana through PROMETEO/2017/139 and program CDEIGENT/2018/028.

The interactions of the spins of single atoms with a substrate can be controlled via the moiré lattice created by depositing a 2D material on top of the substrate.

Fractionalization is a phenomenon in which strong interactions in a quantum system drive the emergence of excitations with quantum numbers that are absent in the building blocks. Outstanding examples are excitations with charge e/3 in the fractional quantum Hall effect, solitons in one-dimensional conducting polymers and Majorana states in topological superconductors. Fractionalization is also predicted to manifest itself in low-dimensional quantum magnets, such as one-dimensional antiferromagnetic S = 1 chains. The fundamental features of this system are gapped excitations in the bulk and, remarkably, S = 1/2 edge states at the chain termini, leading to a four-fold degenerate ground state that reflects the underlying symmetry-protected topological order. Here, we use on-surface synthesis to fabricate one-dimensional spin chains that contain the S = 1 polycyclic aromatic hydrocarbon triangulene as the building block. Using scanning tunneling microscopy and spectroscopy at 4.5 K, we probe length-dependent magnetic excitations at the atomic scale in both open-ended and cyclic spin chains, and directly observe gapped spin excitations and fractional edge states therein. Exact diagonalization calculations provide conclusive evidence that the spin chains are described by the S = 1 bilinear-biquadratic Hamiltonian in the Haldane symmetry-protected topological phase. Our results open a bottom-up approach to study strongly correlated quantum spin liquid phases in purely organic materials, with the potential for the realization of measurement-based quantum computation., 23 pages, 4 main figures and 7 extended data figures; supplementary information containing additional data is included

Under the challenge of growing a single bilayer of Bi oriented in the (111) crystallographic direction over amorphous substrates, we have studied different thicknesses of Bi thermally evaporated onto silicon oxide in order to shed light on the dominant atomic structures and their oxidation. We have employed atomic force microscope, X-ray diffraction, and scanning electron microscope approaches to demonstrate that Bi is crystalline and oriented in the (111) direction for thicknesses over 20 nm. Surprisingly, Raman spectroscopy indicates that the rhombohedral structure is preserved even for ultra-thin layers of Bi, down to $\sim 5$ nm. Moreover, the signals also reveal that bismuth films exposed to ambient conditions do not suffer major surface oxidation., 6 pages,4 figures

The search of compounds emitting in the near-infrared (NIR) has been accelerated owing to their use in biomedical and telecommunications applications. In this regard, nanographenes (NGs) are attractive materials adequate for integration with other technologies, which have recently demonstrated amplified spontaneous emission (ASE) and lasing across the visible spectrum. Here, the optical and ASE properties of four-zigzag edged NGs of the [m,n]peri-acenoacene family are reported, whose size is increased through conjugation extension by varying n (from 3 to 5) while keeping m = 2. Results show that such 1D conjugation extension method is more efficient in terms of shifting the photoluminescence (PL) to the infrared (PL at 710 nm in the larger compound, PP-Ar) than through 2D conjugation extension as in previously reported NGs (PL at 676 nm with the largest compound FZ3, with n = 3 and m = 4). Additionally, PP-Ar shows dual-ASE (at 726 and 787 nm), whose origin is elucidated through Raman and transient absorption spectroscopies. These compounds’ potential for red and NIR lasing is demonstrated through the fabrication of distributed feedback lasers with top-layer resonators. This study paves the way towards the development of stable low-cost all-plastic NIR lasers. The authors acknowledge financial support from the “Ministerio de Ciencia, Innovación y Universidades” of Spain, European Regional Development Fund and European Social Funds (MAT2015-66586-R, PDI2019-106114GB-I00, BES-2016-077681, PGC2018-098533-B-100 and RED2018-102815-T). J.C. thanks the Junta de Andalucía of Spain (UMA18FEDERJA057). The authors also thank the Research Central Services (SCAI) of the University of Málaga. F.G. acknowledges the Spanish Government for an FPI grant. G.M.P. thanks Fondazione Cariplo (grant no 2018-0979) for the financial support. J.W. acknowledges the “Agency for Science, Technology and Research of Singapore” for financial support from A*STAR AME grant (A20E5c0089). A.M.R. and F.S. have received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. [816313]).

We study spin excitations and Kondo effect in open-shell nanographenes, motivated by recent scanning tunneling inelastic spectroscopy experiments. Specifically, we consider three systems, the triangulene, the extended triangulene with rocket shape, both with an $S=1$ ground state, and a triangulene dimer with $S=0$ on account of intermolecular exchange. We focus on the consequences of hybridization of the nanographene zero-modes with a conducting substrate on the $dI/dV$ lineshapes associated with spin excitations. The partially filled nanographene zero-modes coupled to the conduction electrons in the substrate constitute multi-orbital Anderson impurity models that we solve in the one-crossing approximation which treats the coupling to the substrate to infinite order. We find that the coupling to the substrate leads to (i) renormalization of the spin flip excitation energies of the bare molecule, (ii) broadening of the spectral features and (iii) the emergence of zero bias Kondo peaks for the $S=1$ ground states. The calculated substrate induced shift of the spin excitation energies is found to be significantly larger than their broadening, which implies that this effect has to be considered when comparing experimental results and theory., Comment: 9 pages, 4 figures; replaced with revised version, accepted in Phys. Rev. B

Van der Waals materials with narrow energy gaps and efficient response over a broadband optical spectral range are key to widen the energy window of nanoscale optoelectronic devices. Here, we characterize FePS as an appealing narrow-gap p-type semiconductor with an efficient broadband photo-response, a high refractive index, and a remarkable resilience against air and light exposure. To enable fast prototyping, we provide a straightforward guideline to determine the thickness of few-layered FePS nanosheets extracted from the optical transmission characteristics of several flakes. The analysis of the electrical photo-response of FePS devices as a function of the excitation energy confirms a narrow gap suitable for near IR detection (1.23 eV) and, more interestingly, reveals a broad spectral responsivity up to the ultraviolet region. The experimental estimate for the gap energy is corroborated by ab-initio calculations. An analysis of photocurrent as a function of gate voltage and incident power reveals a photo-response dominated by photogating effects. Finally, aging studies of FePS nanosheets under ambient conditions show a limited reactivity of the outermost layers of flakes in long exposures to air., The present work has received funding from the European Union’s Horizon 2020 research and innovation program through the European Research Council grants ERC-2017-StG-755655 2D-TOPSENSE, ERC-2018-AdG-788222 MOL-2D, under the Graphene Flagship through projects GrapheneCore2 (grant nr. 785219), and GrapheneCore3 (grant nr. 881603) and through the COST Action CA15128 MOLSPIN. The authors also acknowledge funding from the Spanish Government through the Unit of Excellence “María de Maeztu” MDM-2015-0538, through projects MAT2017- 88377-C2-2-R (AEI/FEDER), MAT2017-88377, MAT2017-89528 (AEI/FEDER), and R.F.’sJuan de la Cierva-formación fellowship FJCI-2017-32919. This work has been supported by the Generalitat Valenciana, through grants CIDEGENT/2018/004, CIDEGENT/2018/005, CDEIGENT/2019/022, the Prometeo Program of Excellence, and M.R.’s APOSTD/2020/249 fellowship.

For the past three decades, nanoscience has widely affected many areas in physics, chemistry, and engineering, and has led to numerous fundamental discoveries as well as applications and products. Concurrently, quantum science and technology has developed into a cross-disciplinary research endeavour connecting these same areas and holds a burgeoning commercial promise. Although quantum physics dictates the behaviour of nanoscale objects, quantum coherence, which is central to quantum information, communication and sensing has not played an explicit role in much of nanoscience. This Review describes fundamental principles and practical applications of quantum coherence in nanoscale systems, a research area we call quantum-coherent nanoscience. We structure this manuscript according to specific degrees of freedom that can be quantum-coherently controlled in a given nanoscale system such as charge, spin, mechanical motion, and photons. We review the current state of the art and focus on outstanding challenges and opportunities unlocked by the merging of nanoscience and coherent quantum operations., Comment: 34 pages, 6 figures, 2 boxes

We study the electronic properties of the heterobilayer of vanadium and iron oxychlorides, VOCl and FeOCl, two layered air stable van der Waals insulating oxides with different types of antiferromagnetic order in bulk: VOCl monolayers are ferromagnetic (FM) whereas the FeOCl monolayers are antiferromagnetic (AF). We use density functional theory (DFT) calculations, with Hubbard correction that is found to be needed to describe correctly the insulating nature of these compounds. We compute the magnetic anisotropy and propose a spin model Hamiltonian. Our calculations show that interlayer coupling in weak and ferromagnetic so that magnetic order of the monolayers is preserved in the heterobilayers providing thereby a van der Waals heterostructure that combines two monolayers with different magnetic order. Interlayer exchange should lead both to exchange bias and to the emergence of hybrid collective modes that that combine FM and AF magnons. The energy band of the heterobilayer show a type II band alignment, and feature spin-splitting of the states of the AF layer due to the breaking of the inversion symmetry., Comment: 6 pages, 3 figures

Nanographenes with zigzag edges are predicted to manifest non-trivial pi-magnetism resulting from the interplay of hybridization of localized frontier states and Coulomb repulsion between valence electrons. This provides a chemically tunable platform to explore quantum magnetism at the nanoscale and opens avenues toward organic spintronics. The magnetic stability in nanographenes is thus far limited by the weak magnetic exchange coupling which remains below the room temperature thermal energy. Here, we report the synthesis of large rhombus-shaped nanographenes with zigzag periphery on gold and copper surfaces. Single-molecule scanning probe measurements unveil an emergent magnetic spin-singlet ground state with increasing nanographene size. The magnetic exchange coupling in the largest nanographene, determined by inelastic electron tunneling spectroscopy, exceeds 100 meV or 1160 K, which outclasses most inorganic nanomaterials and remarkably survives on a metal electrode., 4 figures plus supplementary information

The emergence of local moments in graphene zigzag edges, grain boundaries, vacancies and sp3 defects has been widely studied theoretically. However, conclusive experimental evidence is scarce. Recent progress in on-surface synthesis has made it possible to create nanographenes, such as triangulenes, with local moments in their ground states, and to probe them using scanning tunneling microscope (STM) spectroscopy. Here we review the application of the theory of sequential and cotunneling transport to relate the dI/dV spectra with the spin properties of nanographenes probed by STM. This approach permits us to connect the dI/dV with the many-body energies and wavefunctions of the graphene nanostructures. We apply this method describing the electronic states of the nanographenes by means of exact diagonalization of the Hubbard model within a restricted Active Space. This permits us to provide a proper quantum description of the emergence of local moments in graphene and its interplay with transport. We discuss the results of this theory in the case of diradical nanographenes, such as triangulene, rectangular ribbons and the Clar’s goblet, that have been recently studied experimentally by means of STM spectroscopy. This approach permits us to calculate both the dI/dV spectra, that yields excitation energies, as well as the atomically resolved conductivity maps, that provide information on the wavefunctions of the collective spin modes. We acknowledge financial support from Ministry of Science and Innovation of Spain (grant numbers PID2019-106114GB-I00 and PID2019- 109539GB), from MINECO-Spain (Grant No. MAT2016-78625-C2) and from the Portuguese Fundação para a Ciência e a Tecnologia (FCT) for the projects P2020-PTDC/FIS-NAN/4662/2014, P2020-PTDC/FIS-NAN/3668/2014 and UTAPEXPL/NTec/0046/2017 projects. JFR acknowledges Generalitat Valenciana funding (Prometeo2017/139). R. O. acknowledge ACIF/2018/175 (Generalitat Valenciana and Fondo Social Europeo).

The discovery of ferromagnetic order in monolayer 2D crystals has opened a new venue in the field of two dimensional (2D) materials. 2D magnets are not only interesting on their own, but their integration in van der Waals heterostructures allows for the observation of new and exotic effects in the ultrathin limit. The family of Chromium trihalides, CrI$_3$, CrBr$_3$ and CrCl$_3$, is, so far, the most studied among magnetic 2D crystals. In this mini-review, we provide a perspective of the state of the art of the theoretical understanding of magnetic 2D trihalides, most of which will also be relevant for other 2D magnets, such as vanadium trihalides. We discuss both the well-established facts, such as the origin of the magnetic moment and magnetic anisotropy and address as well open issues such as the nature of the anisotropic spin couplings and the magnitude of the magnon gap. Recent theoretical predictions on Moir\' e magnets and magnetic skyrmions are also discussed. Finally, we give some prospects about the future interest of these materials and possible device applications., Comment: This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Nano Letters, copyright \c{opyright} American Chemical Society after peer review

The analysis of the impact of spin–orbit coupling (SOC) on the Kondo state has generated considerable controversy, mainly regarding the dependence of the Kondo temperature T K on SOC strength. Here, we study the one-dimensional (1D) single impurity Anderson model (SIAM) subjected to Rashba (α) and Dresselhaus (β) SOC. It is shown that, due to time-reversal symmetry, the hybridization function between impurity and quantum wire is diagonal and spin independent (as it is the case for the zero-SOC SIAM), thus the finite-SOC SIAM has a Kondo ground state similar to that for the zero-SOC SIAM. This similarity allows the use of the Haldane expression for T K, with parameters renormalized by SOC, which are calculated through a physically motivated change of basis. Analytic results for the parameters of the SOC-renormalized Haldane expression are obtained, facilitating the analysis of the SOC effect over T K. It is found that SOC acting in the quantum wire exponentially decreases T K while SOC at the impurity exponentially increases it. These analytical results are fully supported by calculations using the numerical renormalization group (NRG), applied to the wide-band regime, and the projector operator approach, applied to the infinite-U regime. Literature results, using quantum Monte Carlo, for a system with Fermi energy near the bottom of the band, are qualitatively reproduced, using NRG. In addition, it is shown that the 1D SOC SIAM for arbitrary α and β displays a persistent spin helix SU(2) symmetry similar to the one for a 2D Fermi sea with the restriction α = β. VL acknowledges a PhD scholarship from the Brazilian Agency Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), process 160071/2015-1, and financial support from the Generalitat Valenciana through Grant reference Prometeo 2017/139. MM acknowledges a PhD scholarship from the Brazilian Agency Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). GBM acknowledges financial support from CNPq, processes 424711/2018-4 and 305150/2017-0. EVA acknowledges financial support from CNPq, process 306000/2017-2.

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

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

[EN] Zigzag edges of neutral armchair–oriented Graphene Nano–Ribbons show states strongly localized at those edges. They behave as free radicals that can capture electrons during processing, increasing ribbon's stability. Thus, charging and its consequences should be investigated. Total energy calculations of finite ribbons using spin–polarized Density Functional Theory (DFT) show that ribbon's charging is feasible. Energies for Pariser-Parr-Pople (PPP) model Hamiltonian are compatible with DFT allowing the study of larger systems. Results for neutral ribbons indicate: i) the fundamental gap of spin–polarized (non–polarized) solutions is larger (smaller) than experimental data, ii) the ground state is spin–polarized, a characteristic still not observed experimentally. Total energy of GNRs decreases with the number of captured electrons reaching a minimum for a number that mainly depends on zigzag–edges size. The following changes with respect to neutral GNRs are noted: i) the ground state is not spin–polarized, ii) fundamental gap is in-between that of spin–polarized and non–polarized solutions of neutral ribbons, iii) while in neutral ribbons valence and conduction band onsets vs. the fundamental gap, linearly and symmetrically approach mid–gap with slope 0.5, charging induces Fermi level pinning, i.e., the slopes of the valence and conduction bands being about 0.1 and 0.9, in agreement with experiment., This work has been Partial financial support by the Spanish “Ministerio de Ciencia, Innovación y Universidades”(Grants FIS2015-64222-C2-1-P, FIS2015-64222-C2-2-P, MAT2016-77742-C2-2-P and AYA2015-66899-C2-2-P), and the Universidad de Alicante is gratefully acknowledged.

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.

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

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

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

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.

Electronic polarizability of finite chains is accurately calculated from the total energy variation of the system produced by small but finite static electric fields applied along the chain direction. Normalized polarizability, that is, polarizability divided by chain length, diverges as the second power of length for metallic systems but approaches a constant value for insulating systems. This behaviour provides a very convenient way to characterize the wave-function malleability of finite systems as it avoids the need of attaching infinite contacts to the chain ends. Hubbard model calculations at half filling show that the method works for a small U = 1 interaction value that corresponds to a really small spectral gap of 0.005 (hopping t = −1 is assumed). Once successfully checked, the method has been applied to the long-range hopping model of Gebhard and Ruckenstein showing 1/r hopping decay (Gebhard and Ruckenstein 1992 Phys. Rev. Lett. 68 244; Gebhard et al 1994 Phys. Rev. B 49 10926). Metallicity for U values below the reported metal-insulator transition is obtained but the surprise comes for U values larger than the critical one (when a gap appears in the spectral density of states) because a steady increase of the normalized polarizability with size is obtained. This critical size-scaling behaviour can be understood as corresponding to a molecule which polarizability is unbounded. We have checked that a real transfer of charge from one chain end to the opposite occurs as a response to very small electric fields in spite of the existence of a large gap of the order of U for one-particle excitations. Finally, ab initio quantum chemistry calculations of realistic poly-acetylene chains prove that the occurrence of such critical behaviour in real systems is unlikely. Financial support by the Spanish Ministerio de Economía y Competitividad (MINECO) (grants FIS2015-64222-C2-1-P and FIS2015-64222-C2-2-P) is gratefully acknowledged.

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)

The successful use of graphene nanoribbons (GNRs) in a variety of applications in nanoelectronics depends not only on reliable control of their forbidden gaps, but also on the understanding of the effects that contacts to leads may have on their conductance G. By combining Landauer's formalism and a simplified version of the embedded cluster method, G through suspended 9-AGNR has been calculated as a function of energy (sample bias) and the strength of the contact between the ribbon and leads attached to both zigzag edges. Green's functions of contacted ribbons have been derived from HF nonspin polarized solutions of the Pariser-Parr-Pople Hamiltonian. It is shown that the G associated with the two quasidegenerate states around the Fermi level, which are strongly localized at the zigzag edges, equals a conductance quantum G0 for very weak leads-ribbon coupling, decreasing to zero as that coupling increases. At the Fermi level G is zero for small coupling, increasing up to G0 for a value of coupling that depends on the GNR length, and, finally, decreasing to zero for large coupling. Conductance through other energies, starting at G=0 for no coupling, increases with coupling to the electrodes up to near one quantum at a pace that may appreciably depend on the particular molecular orbital. These results illustrate the difficulties that may be found in exploring practical uses of GNRs. Financial support by the Spanish “Ministerio de Ciencia, Innovación y Universidades” (Grants FIS2015-64222-C2-1-P and FIS2015-64222-C2-2-P) and the Universidad de Alicante is gratefully acknowledged.

Results of a study of electronic energy loss of low keV protons interacting with multilayer graphene targets are presented. Proton energy loss shows an unexpectedly high value as compared with measurements in amorphous carbon and carbon nanotubes. Furthermore, we observe a classical linear behavior of the energy loss with the ion velocity but with an apparent velocity threshold around 0.1 a.u., which is not observed in other carbon allotropes. This suggests low dimensionality effects which can be due to the extraordinary graphene properties. This work was mainly supported by the grants Fondecyt [grant number 1100759], CONICYT-MEC [grant number 80150073] and DGIIP-UTFSM [grant number 216.11.3]. MM and BF acknowledge the Basal Program for Centers of Excellence, Grant FB0807 CEDENNA, CONICYT. RGM and IA acknowledge financial support provided by the Spanish Ministerio de Economía y Competitividad and the European Regional Development Fund (Project No. FIS2014-58849-P), as well as by the Fundación Séneca (Project No. 19907/GERM/15).

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 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.

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

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 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”.

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

In the present work thermal-nanoimprint lithography of various commercial thermoplastic resists as matrixes for perylenediimides (PDIs) has been studied. This fabrication method reduces the number of fabrication steps, and therefore, the cost of the obtained distributed feedback (DFB) lasers. The optical properties of these devices are analyzed, aiming to optimize their performance. Spanish Government (MINECO) and the European Community (FEDER) through grants MAT2008-06648-C02 and MAT-2011-28167-C02. Manuel G. Ramírez is supported by a CSIC fellowship within the program JAE.

The irradiation of carbon based nanostructures with ions and electrons has been shown to be an appropriate tool to tailor their properties. The defects induced in the nanostructures during irradiation are able to modify their mechanical and electronic properties. Here we simulate the irradiation of carbon nanotubes with carbon ions using a molecular dynamics code. We use the Tersoff potential joined smoothly to the Universal Ziegler-Biersack-Littmark potential at short distances. We study the number of defects produced after irradiation with a single carbon ion finding a saturation with its energy at ∼ 3 keV. We observe, after continuum irradiation with low energy ions, the formation of bumps in the irradiated region. For larger energy ions we find that the diameter of the nanotube shrinks as shown in previous works. This work has been financially supported by Project FIS2010-17225 by the Spanish Ministerio de Ciencia e Innovación.

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 manuscript shows that nano-engineering the surface of diamond particles prior contacting the liquid metal strongly enhances the Thermal Conductivity (TC) of Al/diamond composites. Composites were fabricated by gas pressure infiltration within a two-step engineering procedure: i) diamond surface was in situ subjected to gas desorption by annealing at 760 °C or 850 °C, and, ii) the contact time between liquid metal and diamond was strictly controlled. The synergic action of surface modification and controlled processing conditions allows an outstanding increasing of TC from 422 W/mK to 734 W/mK (around 42% of increment) in composites fabricated with medium-quality diamond particles. The authors acknowledge the “Ministerio de Economía y Competitividad” for partial financial support trough project MAT2011-25,029. I.E. Monje thanks University of Alicante for a UA-FPU Ph.D. fellowship.

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)

Solution-processed polymer films are used in multiple technological applications. The presence of residual solvent in the film, as a consequence of the preparation method, affects the material properties, so films are typically subjected to post-deposition thermal annealing treatments aiming at its elimination. Monitoring the amount of solvent eliminated as a function of the annealing parameters is important to design a proper treatment to ensure complete solvent elimination, crucial to obtain reproducible and stable material properties and therefore, device performance. Here we demonstrate, for the first time to our knowledge, the use of an organic distributed feedback (DFB) laser to monitor with high precision the amount of solvent extracted from a spin-coated polymer film as a function of the thermal annealing time. The polymer film of interest, polystyrene in the present work, is doped with a small amount of a laser dye as to constitute the active layer of the laser device and deposited over a reusable DFB resonator. It is shown that solvent elimination translates into shifts in the DFB laser wavelength, as a consequence of changes in film thickness and refractive index. The proposed method is expected to be applicable to other types of annealing treatments, polymer-solvent combinations or film deposition methods, thus constituting a valuable tool to accurately control the quality and reproducibility of solution-processed polymer thin films. The work was supported by the Spanish Government (MINECO) and the European Community (FEDER) through grant No. MAT-2011-28167-C02-01. M.M.-V. has been partly supported by a MINECO FPI fellowship (No. BES-2009-020747).

The human epidermal growth factor receptor 2 (ErbB2) protein plays an important role in human malignancies. Its overexpression has been recognized as a feature of a malignant cancerous phenotype in breast cancer cell lines, and has become one of the most widely investigated clinical indicators of breast, ovarian, gastrointestinal and lung cancers. In this work a vertically emitting organic distributed feedback (DFB) laser has been used to detect the ErbB2 protein. This DFB laser consists of a polystyrene (PS) film containing a perylenediimide laser dye, deposited over a second-order one dimensional grating fabricated on fused silica by thermal-nanoimprint lithography and subsequent reactive ion etching processes. Specificity of the system to ErbB2 protein biomarker, achieved by functionalizing the PS with anti-ErbB2 monoclonal antibodies, is demonstrated. A concentration limit of detection for ErbB2 protein of 14 ng/mL has been obtained, and no cross-reactivity has been observed with bovine serum albumin (BSA) and tumor necrosis factor alpha (TNFα) proteins. These findings open the possibility of using this type of biosensors in clinical applications. This work was supported by the Spanish Government (MINECO) and the European Community (FEDER) through grant no. MAT-2011–28167-C02. This work was partially funded by the Basque Government within the framework of the Etortek Program (Grant No. IE13-360). M. Morales-Vidal has been partly supported by a MINECO FPI fellowship (no. BES-2009-020747).

Spin orbit coupling changes graphene, in principle, into a two-dimensional topological insulator, also known as quantum spin Hall insulator. One of the expected consequences is the existence of spin-filtered edge states that carry dissipationless spin currents and undergo no back-scattering in the presence of non-magnetic disorder, leading to quantization of conductance. Whereas, due to the small size of spin orbit coupling in graphene, the experimental observation of these remarkable predictions is unlikely, the theoretical understanding of these spin-filtered states is shedding light on the electronic properties of edge states in other two-dimensional quantum spin Hall insulators. Here we review the effect of a variety of perturbations, like curvature, disorder, edge reconstruction, edge crystallographic orientation, and Coulomb interactions on the electronic properties of these spin filtered states., Comment: 9 pages, 10 figures

We consider dilute magnetic doping in the surface of a three dimensional topological insulator where a two dimensional Dirac electron gas resides. We find that exchange coupling between magnetic atoms and the Dirac electrons has a strong and peculiar effect on both. First, the exchange-induced single ion magnetic anisotropy is very large and favors off-plane orientation. In the case of ferromagnetically ordered phase we find a colossal magnetic anisotropy energy, of the order of the critical temperature. Second, a persistent electronic current circulates around the magnetic atom and, in the case of a ferromagnetic phase, around the edges of the surface., Comment: 4 pages, 3 figures

This experimental work aims at probing current-induced forces at the atomic scale. Specifically it addresses predictions in recent work regarding the appearance of run-away modes as a result of a combined effect of the non-conservative wind force and a ‘Berry force’. The systems we consider here are atomic chains of Au and Pt atoms, for which we investigate the distribution of break down voltage values. We observe two distinct modes of breaking for Au atomic chains. The breaking at high voltage appears to behave as expected for regular break down by thermal excitation due to Joule heating. However, there is a low-voltage breaking mode that has characteristics expected for the mechanism of current-induced forces. Although a full comparison would require more detailed information on the individual atomic configurations, the systems we consider are very similar to those considered in recent model calculations and the comparison between experiment and theory is very encouraging for the interpretation we propose. This work is 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), and is supported by the Spanish government through grant FIS2013-47328, the Conselleria d’Educació of the Generalitat Valenciana through grant PROMETEO/2012/011.

The inelastic mean free path (IMFP) of electrons with energies up to a few keV is calculated from the dielectric electron-gas theory for densities corresponding to those of biological matter. The effect of the many-body local-field correction on the Lindhard dielectric response function is examined using some of the available analytical approximations to its static limit. We have tested the performance of several Hubbard-type local-field corrections along with the formula proposed by Corradini and co-workers [M. Corradini, R. Del Sole, G. Onida, M. Palumno, Phys. Rev. B 57 (1998) 14569] which is extensively used in connection with the exchange-correlation kernel of time-dependent density functional theory. It is shown that the Lindhard dielectric function provides reasonable estimates of electron IMFPs below about 50 eV, where the majority of semi-empirical dielectric calculations based on the extended-optical-data methodology fail. The use of LFC results in a sizeable reduction of the IMFP which, at low energies, may reach ∼20%. DE and IK acknowledge financial support by the European Union FP7 ANTICARB (HEALTH-F2-2008-201587) research programme and by an internal grand from the Research Committee of the University of Ioannina (Grant No. 80037). IA and RGM acknowledge financial support by the Spanish Ministerio de Educación y Ciencia (Projects FIS2006-13309-C02-01 and FIS2006-13309-C02-02).

The optical energy-loss function (ELF) of Au and Al, obtained from experiments, is extended to finite wavenumber k using three different widely used models, namely, with the Mermin type ELFs with generalized oscillator strengths (MELF-GOS) model, the extended Drude model and the Penn model. The resulting ELFs show important differences but the MELF-GOS model gives more realistic results when compared with the available experimental ELFs for finite k. These differences affect calculations of important parameters in projectile-solid interaction. The calculated stopping power and energy-loss straggling of Au and Al for H projectiles as well as the corresponding inelastic mean free path (IMFP) of electrons in Au and Al clearly show that the results depend on the model used for the ELF description. Comparison with experimental data gives support to the MELF-GOS model, especially in a material with a complex energy-loss spectrum such as Au. This work was supported by the Spanish Ministerio de Educación y Ciencia (Projects FIS2006-13309-C02-01 and FIS2006-13309-C02-02) and Universitat d’Alacant by Project GRE07-1P. CDD thanks the Spanish Ministerio de Educación y Ciencia and Generalitat Valenciana for support under the Ramón y Cajal Program.

Model Hamiltonians have been, and still are, a valuable tool for investigating the electronic structure of systems for which mean field theories work poorly. This review will concentrate on the application of Pariser-Parr-Pople (PPP) and Hubbard Hamiltonians to investigate some relevant properties of polycyclic aromatic hydrocarbons (PAH) and graphene. When presenting these two Hamiltonians we will resort to second quantisation which, although not the way chosen in its original proposal of the former, is much clearer. We will not attempt to be comprehensive, but rather our objective will be to try to provide the reader with information on what kinds of problems they will encounter and what tools they will need to solve them. One of the key issues concerning model Hamiltonians that will be treated in detail is the choice of model parameters. Although model Hamiltonians reduce the complexity of the original Hamiltonian, they cannot be solved in most cases exactly. So, we shall first consider the Hartree-Fock approximation, still the only tool for handling large systems, besides density functional theory (DFT) approaches. We proceed by discussing to what extent one may exactly solve model Hamiltonians and the Lanczos approach. We shall describe the configuration interaction (CI) method, a common technology in quantum chemistry but one rarely used to solve model Hamiltonians. In particular, we propose a variant of the Lanczos method, inspired by CI, that has the novelty of using as the seed of the Lanczos process a mean field (Hartree-Fock) determinant (the method will be named LCI). Two questions of interest related to model Hamiltonians will be discussed: (i) when including long-range interactions, how crucial is including in the Hamiltonian the electronic charge that compensates ion charges? (ii) Is it possible to reduce a Hamiltonian incorporating Coulomb interactions (PPP) to an 'effective' Hamiltonian including only on-site interactions (Hubbard)? The performance of CI will be checked on small molecules. The electronic structure of azulene and fused azulene will be used to illustrate several aspects of the method. As regards graphene, several questions will be considered: (i) paramagnetic versus antiferromagnetic solutions, (ii) forbidden gap versus dot size, (iii) graphene nano-ribbons, and (iv) optical properties., Financial support by the Spanish 'Ministerio de Ciencia e Innovación MICINN' (grants FIS2009-10325, FIS2009-08744, FIS2012-33521 and FIS2012-35880) and the Universidad de Alicante is gratefully acknowledged. We also acknowledge support from the DGUI of the Comunidad de Madrid under the R&D Program of activities MODELICO-CM/S2009ESP-1691.