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We demonstrate the novel growth of silicene grown on Ag(111) using STM and reveal the mechanism with KMC simulation. Our STM study shows that after the complete formation of the first layer of silicene, it is transformed into bulk Si with the reappearance of the bare Ag surface. This dewetting (DW) during the epitaxial growth is an exception in the conventional growth behavior. Our KMC simulation reproduces DW by taking into account the differences in the activation energies of Si atoms on Ag, silicene, and bulk Si. The growth modes change depending on the activation energy of the diffusion, temperature, and deposition rate, highlighting the importance of kinetics in growing metastable 2D materials.

The effects of adsorption of Zn-phthalocyanine (ZnPc) molecules on the superconductivity of the Si(111)-(root7xroot3)-In surface are studied through transport measurements under ultrahigh vacuum environment. The ZnPc molecules are found to increase the transition temperature Tc by 11% at maximum, which is about 2.7 times the Tc increase previously reported using CuPc. By contrast, angle-resolved photoemission spectroscopy measurements and ab initio calculations show that charge transfer from the In atomic layers to ZnPc is substantially smaller than that to CuPc. This clearly shows that charge transfer should be excluded as the origin of the increase in Tc. The push-back effect induced by physical adsorption of molecules is discussed as a possible mechanism for the Tc enhancement.

In this study, ab initio calculations were performed to show that the superconductivity in Li-intercalated bilayer MoS2 could be enhanced by applying either compressive or tensile strain. Moreover, the mechanism for superconductivity enhancement for the tensile strain case was found to be different than that of the compressive strain case. Enhanced electron phonon coupling (EPC) under tensile strain could be explained by an increase in the nesting function involved with the change in the Fermi surface topology in a wide range of Brillouin zones. The superconducting transition temperature Tc of 0.46 K at zero strain increased up to 9.12 K under a 6.0% tensile strain. Meanwhile, the enhancement in compressive strain was attributed to the increase in intrinsic electron phonon matrix elements. Furthermore, the contribution from interband scattering was large, which suggested the importance of electron pockets on the Fermi surface. Finally, 80% of the total EPC (λ = 0.98) originated from these pockets and the estimated Tc was 13.50 K.

Yu-Shiba-Rusinov (YSR) states arise when magnetic impurities interact with superconductivity. The intricacy of coupling and the nature of the superconductivity determine the behavior of the YSR state, whose detailed correlations are not yet fully understood. Here, we study the YSR state of a single Fe adatom on the surface of 2H-NbSe2 with combined low temperature scanning tunneling microscopy/spectroscopy, density functional theory calculations and tight-binding modeling. It is found that the Fe adatom occupies the hollow site of the Se surface layer. A prominent YSR state close to the Fermi level is observed. The YSR state exhibits a threefold symmetry along the diagonal direction of the Se lattice. The spatial decay of the YSR state follows a behavior in three-dimensional superconductivity. This behavior contrasts with a previous study of imbedded Fe impurities, whose YSR state shows a six-fold symmetry and a two-dimensional long-range decay. According to our theoretical modeling, the coupling configurations affect the adatom-substrate hopping and the interlayer coupling of the substrate. Both factors are crucial for the consequent behavior of the YSR state.

An interface of molecule and metal has attracted much attention in the research field of nanoelectronics because of their high degree of design freedom. Here, we demonstrate an efficient spin-to-charge current conversion at the metal surface covered by a single layer of molecules. Spin currents are injected into an interface between metal (Cu) and lead(II) phthalocyanine by means of the spin pumping method. An observed voltage signal is caused by the inverse Edelstein effect, i.e., spin-to-charge current conversion at the interface. The conversion coefficient, inverse Edelstein length, is estimated to be 0.40 ± 0.06 nm, comparable with the largest Rashba spin splitting of interfaces with heavy metals. Interestingly, the Edelstein length strongly depends on the thickness of the molecule and takes a maximum value when a single layer of molecules is formed on the Cu surface. Comparative analysis between scanning probe microscopy and first-principles calculations reveal that the formation of interface state with Rashba spin splitting causes the inverse Edelstein effect, whose magnitude is sensitive to the adsorption configuration of the molecules.

The coexistence and competition of superconductivity and magnetism can lead to a variety of rich physics and technological applications. In this respect, recent discovery of atomic-layer superconductors offers opportunities to create new kinds of van der Waals two-dimensional (2D) heterostructures if magnetic molecules are self-assembled on the surface. Here we report on highly ordered 2D hybrid superconductors based on indium atomic layers on silicon surfaces and iron-phthalocyanine (FePc). Superconductivity was found to persist in the presence of spin magnetic moments of a closely packed FePc layer and its exchange-interaction with conduction electrons. This is in marked contrast to the previously reported strong suppression of superconductivity by manganese-phthalocyanine (MnPc), which has magnetic properties analogous to those of FePc. The origin of the distinctive behaviours of these heterostructures is discussed in terms of the Kondo effect as well as charge transfer and the exchange interaction between the two layers.

Quantifying the correlation between the complex structures of amorphous materials and their physical properties has been a longstanding problem in materials science. In amorphous Si, a representative covalent amorphous solid, the presence of a medium-range order (MRO) has been intensively discussed. However, the specific atomic arrangement corresponding to the MRO and its relationship with physical properties, such as thermal conductivity, remains elusive. We solved this problem by combining topological data analysis, machine learning, and molecular dynamics simulations. Using persistent homology, we constructed a topological descriptor that can predict thermal conductivity. Moreover, from the inverse analysis of the descriptor, we determined the typical ring features correlated with both the thermal conductivity and MRO. The results could provide an avenue for controlling material characteristics through the topology of the nanostructures.

Inelastic electron tunneling spectroscopy (IETS) combined with scanning tunneling microscopy (STM) allows the acquisition of vibrational signals at surfaces. In STM-IETS, a tunneling electron may excite a vibration, and opens an inelastic channel in parallel with the elastic one, giving rise to a change in conductivity of the STM junction. Until recently, the application of STM-IETS was limited to the localized vibrations of single atoms and molecules adsorbed on surfaces. The theory of the STM-IETS spectrum in such cases has been established. For the collective lattice dynamics, i.e., phonons, however, features of STM-IETS spectrum have not been understood well, though in principle STM-IETS should also be capable of detecting phonons. In this review, we present STM-IETS investigations for surface and interface phonons and provide a theoretical analysis. We take surface phonons on Cu(1 1 0) and interfacial phonons relevant to graphene on SiC substrate as illustrative examples. In the former, we provide a theoretical formalism about the inelastic phonon excitations by tunneling electrons based on the nonequilibrium Green’s function (NEGF) technique applied to a model Hamiltonian constructed in momentum space for both electrons and phonons. In the latter case, we discuss the experimentally observed spatial dependence of the STM-IETS spectrum and link it to local excitations of interfacial phonons based on ab-initio STM-IETS simulation.

Phonon angular momentum can be nonzero in the system without inversion or time-reversal symmetry. In previous theory [1], the phonon angular momentum becomes nonzero in the system without time-reversal symmetry. In this chapter, we focus on the phonon in the sysmte without inversion symmetry. When the system has time-reversal symmetry and does not have inversion symmetry, the phonon angular momentum of each phonon mode \(\mathbf {l}_{\sigma }(\mathbf {k})\) is an odd function of wave vector \(\mathbf {k}\).

To determine the correlation between local structure and thermal conductivity of amorphous carbon, we investigated heat conduction in 216-atom systems with different densities (2.0–3.4 g/cm3) using the ab initio molecular dynamics approach. By applying the Allen–Feldman theory with interatomic force constants from ab initio calculations, we report a significant correlation between the thermal conductivity and the density. To clarify which structural characteristics in the high- and low-density cases determine the magnitude of thermal conductivity, we performed geometrical and topological analyses. Coordination number analysis and ring statistics revealed that the sp/sp2/sp3 bond ratios and topological characteristics correlate with density. We also demonstrated that these structural characteristics can be quantified using persistent homology analysis, providing a predictive model of thermal conductivity.

We investigated the $5d$ element substitution effect on the thermal conductivity in $\mathrm{F}{\mathrm{e}}_{2}\mathrm{VAl}$-based superlattice thin films epitaxially grown on a MgO (100) substrate. We found unique crossover behavior in the period dependences of thermal conductivity for Ta-free $\mathrm{F}{\mathrm{e}}_{2}\mathrm{VAl}$ and $\mathrm{F}{\mathrm{e}}_{2}(\mathrm{V},\mathrm{Ta})\mathrm{Al}$-based superlattices. The $\mathrm{F}{\mathrm{e}}_{2}(\mathrm{V},\mathrm{Ta})\mathrm{Al}$-based superlattices with periods more than 40 nm appeared to have much lower thermal conductivity than Ta-free $\mathrm{F}{\mathrm{e}}_{2}\mathrm{VAl}$-based superlattices due to the substitution of V by Ta. Unexpectedly, at a shorter periodic length, less than 20 nm, $\mathrm{F}{\mathrm{e}}_{2}(\mathrm{V},\mathrm{Ta})\mathrm{Al}$-based superlattices appeared to have higher thermal conductivity than Ta-free $\mathrm{F}{\mathrm{e}}_{2}\mathrm{VAl}$-based superlattices despite such a heavy element substitution by Ta. This surprising experimental fact was well accounted for with theoretical calculations, which predicted the dominant contribution of phonons having a shorter mean free path in the Ta substituted samples.

The miscibility of Au and Li exhibits a potential application as an adhesion layer and electrode material in secondary batteries. Here, to explore alloying properties, we constructed a neural network potential (NNP) of Au-Li binary systems based on density functional theory (DFT) calculations. To accelerate construction of NNPs, we proposed an efficient and inexpensive method of structural dataset generation. The predictions by the constructed NNP on lattice parameters and phonon properties agree well with those obtained by DFT calculations. We also investigated the mixing energy of Au$_{1-x}$Li$_{x}$ with fine composition grids, showing excellent agreement with DFT verifications. We found the existence of various compositions with structures on and slightly above the convex hull, which can explain the lack of consensus on the Au-Li stable phases in previous studies. Moreover, we newly found Au$_{0.469}$Li$_{0.531}$ as a stable phase, which has never been reported elsewhere. Finally, we examined the alloying process starting from the phase separated structure to the complete mixing phase. We found that when multiple adjacent Au atoms dissolved into Li, the alloying of the entire Au/Li interface started from the dissolved region. This paper demonstrates the applicability of NNPs toward miscible phases and provides the understanding of the alloying mechanism., 9 pages, 11 figures

In this study

We investigated the possibility of superconductivity in monolayer hexagonal boron nitride (h-BN) doped using group-1 (Li, Na, K) and group-2 (Be, Mg, Ca, Sr, Ba) atoms via ab initio calculations. Consequently, we reveal that Sr- and Ba-doped monolayer h-BN and Ca-doped monolayer h-BN with 3.5% tensile strain are energetically stable and become superconductors with superconducting transition temperature (Tc) values of 5.83, 1.53, and 10.7 K, respectively, which are considerably higher than those of Ca-, Sr-, and Ba-doped graphene. In addition, the momentum-resolved electron-phonon coupling (EPC) constant shows that the scattering among intrinsic π* electrons around the Γ point governs Tc. The scattering process is mediated by the low-energy vibration of the adsorbate. Moreover, compared with graphene, the stronger adsorbate-substrate interaction and lower symmetry in h-BN are critical for enhancing the EPC in doped h-BN.

Topological materials have become promising materials for next-generation devices by utilizing their exotic electronic states. Their exotic states caused by spin-orbital coupling usually locate on the surfaces or at the edges. Scanning tunneling spectroscopy (STS) is a powerful tool to reveal the local electronic structures of condensed matters. Therefore, STS provides us with an almost perfect method to access the exotic states of topological materials. In this topical review, we report the current investigations by several methods based on the STS technique for layered topological material from transition metal dichalcogenide Weyl semimetals (WTe2 and MoTe2) to two dimensional topological insulators (layered bismuth and silicene). The electronic characteristics of these layered topological materials are experimentally identified.

We report a new type of spin-orbit coupling (SOC) called geometric SOC. Starting from the relativistic theory in curved space, we derive an effective nonrelativistic Hamiltonian in a generic curve embedded into flat three dimensions. The geometric SOC is $O(m^{-1})$, in which $m$ is the electron mass, and hence much larger than the conventional SOC of $O(m^{-2})$. The energy scale is estimated to be a hundred meV for a nanoscale helix. We calculate the current-induced spin polarization in a coupled-helix model as a representative of the chirality-induced spin selectivity. We find that it depends on the chirality of the helix and is of the order of $0.01 \hbar$ per ${\rm nm}$ when a charge current of $1~{\rm \mu A}$ is applied., Comment: 7 pages, 2 figures

We investigated Li-ion distribution profiles at the interfaces between $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Li}}_{3}{\mathrm{PO}}_{4}$ and metal electrodes using first-principles and one-dimensional continuum-model calculations. Within the allowed range of the chemical potential of Li in $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Li}}_{3}{\mathrm{PO}}_{4}$, $\ensuremath{-}6.11\phantom{\rule{0.16em}{0ex}}\mathrm{eV}\phantom{\rule{4pt}{0ex}}\ensuremath{\le}{\ensuremath{\mu}}_{\mathrm{Li}}\ensuremath{\le}\phantom{\rule{4pt}{0ex}}\ensuremath{-}2.59\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, which is estimated from the chemical potential diagram of Li, P, O-related chemical compounds, we predict upward band bending near Au(111) and Ni(111) interfaces. We found interstitial Li-ion accumulation for the larger ${\ensuremath{\mu}}_{\mathrm{Li}}$ values and its depth is ca. 3 \AA{} for ${\ensuremath{\mu}}_{\mathrm{Li}}=\ensuremath{-}2.59\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. For the Li(100) interface with ${\ensuremath{\mu}}_{\mathrm{Li}}=\ensuremath{-}2.59\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, we predict slight upward band bending and the formation of interstitial Li-ions. However, the downward band bending occurs for ${\ensuremath{\mu}}_{\mathrm{Li}}=\ensuremath{-}6.11\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, where the accumulated charge carrier corresponds to the Li-ion vacancies. Finally, we suggest that the interstitial Li-ions accumulated within a few \AA{} from the Au(111) interface and the Li-Au alloying play a central role in the switching of the novel memory device.

Localized electronic spin state in molecules has a relatively long spin lifetime and has thus attracted much attention. In this study, we characterize the magnetoresistance of a system comprising Pt and Fe(II)-phthalocyanine (FePc) molecules. The magnetoresistance measurement with the weak antilocalization analysis reveals that a magnetic moment in FePc acts as magnetic impurities for conduction electrons in Pt. Moreover, we find that the magnetoresistance involves a component that possesses the same symmetry as spin-Hall magnetoresistance. These results reveal the spin-angular momentum transfer from metallic Pt to a magnetic moment in FePc molecules, which can be used as a spin torque in a molecular system.

Thermal management is critical in devices that use amorphous semiconductors. Recent studies have revealed how size and mass disorder affect heat conduction, but the effects of more-extreme mass and lattice disorder are also relevant. Here, we report modal analysis of simulated samples of amorphous silicon alloyed with atoms of different-mass silicon to yield a ternary amorphous material. Although we expected the material with high degrees of mass disorder to show dramatic changes in thermal conductivity as the composition of the material changed, the thermal conductivity instead changed monotonically. Thus, we find that no peculiar thermal transport properties appear in ternary amorphous alloys with high degrees of mass disorder. Furthermore, we find that while delocalized propagating modes (propagons) explain nearly 30% of the overall thermal conductivity independent of the composition, the contribution of delocalized non-propagating modes (diffusons) is sensitive to the composition and tends to be the dominant mechanism behind heat conduction in ternary amorphous alloys.

Self-assembled organic molecules can potentially be an excellent source of charge and spin for two-dimensional (2D) atomic-layer superconductors. Here we investigate 2D heterostructures based on In atomic layers epitaxially grown on Si and highly ordered metal-phthalocyanine (MPc, M = Mn, Cu) through a variety of techniques: scanning tunneling microscopy, electron transport measurements, angle-resolved photoemission spectroscopy, X-ray magnetic circular dichroism, and ab initio calculations. We demonstrate that the superconducting transition temperature (Tc) of the heterostructures can be modified in a controllable manner. Particularly, the substitution of the coordinated metal atoms from Mn to Cu is found to reverse the Tc shift from negative to positive directions. This distinctive behavior is attributed to a competition of charge and spin effects, the latter of which is governed by the directionality of the relevant d-orbitals. The present study shows the effectiveness of molecule-induced surface dopin...

We demonstrate that a high-dimensional neural network potential (HDNNP) can predict the lattice thermal conductivity of semiconducting materials with an accuracy that is comparable to that of density functional theory (DFT) calculation. After a training procedure based on force, the root mean square error between the forces predicted by HDNNP and DFT is less than 40 meV Å−1. As typical examples, we present the results of Si and GaN bulk crystals. The deviation from the thermal conductivity calculated using DFT is within 1% at 200 to 500 K for Si and within 5.4% at 200 to 1000 K for GaN.

We investigate the atom-specific interfacial electronic properties of the epitaxial graphene on Si-terminated SiC substrate using density functional theory (DFT) calculation with van der Waals interaction correction, focusing on the dependency of the local electronic state on the chemical environment. The band structure projected on the respective atomic orbitals of the carbon atoms in the buffer layer and uppermost Si atoms demonstrates that the dangling bonds of these atoms form band structures around the Fermi level. The contribution of each atom to the dangling bond states strongly depends on the chemical environment, i.e., the presence/absence of the interlayer Si-C covalent bond. This difference also affects the atom-specific local density of states of the top-layer graphene through its interaction with the substrate/buffer layer. We demonstrate that the bias voltage dependency of the scanning tunneling spectroscopy (STS) mapping image clearly reflects the presence of the dangling bonds of the buffer layer carbon or uppermost Si atom in the substrate, which would enable the detection of the buried dangling bond with an atomic spatial resolution via STS.

We present a combined experimental and theoretical study of electron confinement in graphene nanoislands (GNs) grown on a Pt(111) substrate using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. We observed standing wave patterns in the STM images of GNs, and the bias dependency of the standing wave pattern was reproduced by considering free electrons with an effective mass of m* ≈ (0.27 ± 0.03)me. Because the effective mass of Pt is m* = 0.28me, our results reveal that the electron confinement is due to the effect of the Pt substrate rather than the massless Dirac electrons of graphene. Our calculated maps of the local density of states (LDOS) for the GNs confirm that the electronic properties of the confinement may be described in terms of electrons with an effective mass. The DFT-calculated charge distribution for graphene on the Pt system also shows a clear hybridization between the pz orbitals of both the first layer of the Pt substrate and the carbon atoms.

Detection of lattice strain is crucial for various studies in a nanometer scale because it largely modifies the local electronic states and thus various physical and chemical properties. Here, we demonstrate that the Kondo effect in a single magnetic atom on a metal surface can be a quantum sensor for the local lattice strain. Using low-temperature scanning tunneling spectroscopy, we measured the Kondo resonance in a Co adatom on partially N-adsorbed Cu(001) surfaces, which consist of nanoislands of the Cu 2N monolayer and the clean Cu(001) surface compressed by the surrounding Cu 2N nanoislands. The observed Kondo temperature at the compressed clean surface depends on the area size of the surface, i . e ., the strength of the local lattice strain. This behavior is attributed to the change in the distance between the Co adatom and Cu surface due to the surface lattice strain, which is supported by our density functional calculations. These results provide a way to detect the local strain on the sub-angstrom scale by using the sensitivity of quantum many-body effects.

Phonon modes in crystals can have angular momenta in general. It nevertheless cancels in equilibrium when the time-reversal symmetry is preserved. In this paper we show that when a temperature gradient is applied and heat current flows in the crystal, the phonon distribution becomes off-equilibrium, and a finite angular momentum is generated by the heat current. This mechanism is analogous to the Edelstein effect in electronic systems. This effect requires crystals with sufficiently low crystallographic symmetries, such as polar or chiral crystal structures. Because of the positive charges of the nuclei, this phonon angular momentum induces magnetization. In addition, when the crystal can freely rotate, this generated phonon angular momentum is converted to a rigidbody rotation of the crystal, due to the conservation of the total angular momentum. Furthermore, in metallic crystals, the phonon angular momentum will be partially converted into spin angular momentum of electrons., 10 pages, 6 figures, to appear in Phys. Rev. Lett

The electronic structure of type-II Weyl semimetal molybdenum ditelluride (MoTe

To clarify atomic diffusion in amorphous materials, which is important in novel information and energy devices, theoretical methods having both reliability and computational speed are eagerly anticipated. In the present study, we applied neural network (NN) potentials, a recently developed machine learning technique, to the study of atom diffusion in amorphous materials, using Li

Silicene, a two-dimensional honeycomb sheet consisting of Si atoms, has attracted much attention as a new low-dimensional material because it gains various fascinating characteristics originating from the combination of Dirac fermion features with spin–orbit coupling. The novel properties such as the quantum spin Hall effect and the compatibility with the current Si device technologies have fueled competition to realize the silicene. This review article focuses on the geometric and electronic structures of silicene grown on Ag(1 1 1) investigated by scanning tunneling microcopy (STM), low energy electron diffraction (LEED) and density functional theory (DFT) calculations. The silicene on Ag(1 1 1) takes locally-buckled structure in which the Si atoms are displaced perpendicularly to the basal plane. As a result, several superstructures such as 4 × 4 , 13 × 13 R 13.9 ° , 4 / 3 × 4 / 3 , and etc. emerge. The atomic arrangement of the 4 × 4 silicene has been determined by STM, DFT calculations and LEED dynamical analysis, while the other superstructures remain to be fully-resolved. In the 4 × 4 silicene, Si atoms are arranged to form a buckled honeycomb structure where six Si atoms of 18 Si atoms in the unit cell are displaced vertically. The displacements lead to the vertical shift of the substrate Ag atoms, indicating the non-negligible coupling at the interface between the silicene layer and the substrate. The interface coupling significantly modifies the electronic structure of the 4 × 4 silicene. No Landau level sequences were observed by scanning tunneling spectroscopy (STS) with magnetic fields applied perpendicularly to the sample surface. The DFT calculations showed that the π and π ∗ bands derived from the Si 3p z are hybridized with the Ag electronic states, leading to the drastic modification in the band structure and then the absence of Dirac fermion features together with the two-dimensionality in the electronic states. These findings demonstrate that the strong coupling at the interface causes the symmetry breaking for the 4 × 4 silicene and as a result the disappearance of Dirac fermion features. The geometric and electronic structures of other superstructures are also discussed.

Epitaxial graphene on SiC that provides wafer-scale and high-quality graphene sheets on an insulating substrate is a promising material to realize graphene-based nanodevices. The presence of the insulating substrate changes the physical properties of free-standing graphene through the interfacial phonon, e.g., limiting the mobility. Despite such known impacts on the material properties, a complete and microscopic picture is missing. Here, we report on atomically resolved inelastic electron tunneling spectroscopy (IETS) with a scanning tunneling microscope for epitaxial graphene grown on $4H$-SiC(0001). Our data reveal a strong spatial dependence in the IETS spectrum, which cannot be explained by intrinsic graphene properties. We show that this variation in the IETS spectrum originates from a localized low-energy vibration of the interfacial Si atom with a dangling bond via ab initio electronic and phononic state calculations. This insight may help advancing graphene device performance through interfacial control.

By using the combination of the ab initio density functional theory and data mining of the Inorganic Crystal Structure Database, a series of monolayer materials are found to be suitable substrates for germanene or stanene, including some of the $\mathrm{Cd}{\mathrm{I}}_{2}$-type materials, CuI, and GaGeTe. All of the found materials, when they are used as the substrate, can almost preserve the quasifreestanding geometry, stability, and band structure of germanene or stanene. Among them, $\mathrm{Cd}{\mathrm{I}}_{2}$ and $\mathrm{Zn}{\mathrm{I}}_{2}$ can open a relatively large band gap of 0.16--0.18 (0.13--0.16) eV [without (with) spin-orbit coupling] in germanene, while preserving Dirac-cone-like band structures. Moreover, the ${Z}_{2}$ invariants of germanene on CuI and stanene on $\mathrm{Ca}{\mathrm{I}}_{2}$ are found to be nontrivial. The interaction between germanene and substrates can be well modeled by the low-energy tight-binding Hamiltonian of germanene under external fields. Our analysis based on the tight-binding Hamiltonian shows that suitable substrates mainly act like a ``pseudoelectric'' field on germanene, and that strong linear correlations are seen among the ``pseudoelectric'' field, extrinsic Rashba coefficient, and charge transfer.

Unique superconductivity at surfaces/interfaces, as exemplified by LaAlO3/SrTiO3 interfaces, and the high transition temperature in ultrathin FeSe films, have triggered intense debates on how superconductivity is affected in atomic and electronic reconstructions. The surface of superconducting cubic spinel oxide LiTi2O4 is another interesting system because its inherent surface electronic and atomic reconstructions add complexity to superconducting properties. Investigations of such surfaces are hampered by the lack of single crystals or high-quality thin films. Here, using low-temperature scanning tunnelling microscopy and spectroscopy, we report an unexpected small superconducting energy gap and a long coherence length on the surface of LiTi2O4(111) epitaxial thin films. Furthermore, we find that a pseudogap opening at the Fermi energy modifies the surface superconductivity. Our results open an avenue for exploring anomalous superconductivity on the surface of cubic transition-metal oxides, where the electronic states are spontaneously modulated involving rich many-body interactions., Atomic and electronic reconstructions at surfaces/interfaces bring about various emergent phenomena. Here, Okada et al. report an unexpected superconducting gap and a long coherence length on the surface of LiTi2O4 (111) thin films.

Structural flexibility of molecule-based systems is key to realizing the novel functionalities. Tuning the structure in the atomic scale enables us to manipulate the quantum state in the molecule-based system. Here we present the reversible Hamiltonian manipulation in a single-molecule quantum dot consisting of an iron phthalocyanine molecule attached to an Au electrode and a scanning tunnelling microscope tip. We precisely controlled the position of Fe2+ ion in the molecular cage by using the tip, and tuned the Kondo coupling between the molecular spins and the Au electrode. Then, we realized the crossover between the strong-coupling Kondo regime and the weak-coupling regime governed by spin–orbit interaction in the molecule. The results open an avenue to simulate low-energy quantum many-body physics and quantum phase transition through the molecular flexibility., Tuning the structure in the atomic scale enables manipulation of the quantum state in a molecular based system. Here, Hiraoka et al. tune the Kondo coupling between molecular spins and the Au electrode by controlling the position of Fe2+ ions in the molecular cage with a tip.

Low energy electron diffraction (LEED), low temperature scanning tunneling microscopy (STM) and density functional theory (DFT) based calculations were used to determine the evolution of the silicene structure on a Ag(111) surface. The phase diagram of the structure was obtained using LEED patterns. The corresponding atomic arrangements were confirmed using STM observations. Results show that the structure of silicene is controlled by the substrate temperature during deposition. Finally, we succeeded in synthesizing silicene on silicene/Ag(111), i.e. bilayer silicene.

We present a model Hamiltonian approach to evaluate the effect of adsorption on magnetic anisotropy of an iron-phthalocyanine (FePc) molecule. We describe the electronic ground state as a mixed configuration consisting of the $^{3}E$ and $^{3}B_{2}$ states under the ${C}_{4v}$ symmetry, which well reproduces the magnetic properties measured for the bulk FePc. We focus on the deformation of each $3d$ orbital and the modification of the ligand-field splitting by hybridization with the substrate electronic states. As an interesting example, we evaluate the $d$-orbital deformation in FePc on Au(111) from the density functional theory calculations, and demonstrate that the respective $d$-orbital deformation and the modification of the ligand-field splitting affect magnetic anisotropy through change of the mixed nature in the ground state. In addition, we propose that inelastic electron tunneling spectroscopy with a cryogenic scanning tunneling microscope is a promising tool to verify the mixed configuration by measuring the low-energy excited states and evolutions to external magnetic fields.

We carry out inelastic electron tunneling spectroscopy (IETS) measurement on a clean Cu(110) surface at 2 K using a scanning tunneling microscope (STM). The spectrum exhibits a single peak at 6 meV, while the phonon density of states (DOS) cannot explain the appearance of this peak. In order to elucidate the origin of the observed peak, we derive a general expression of STM-IETS spectrum for the phonon excitation at a clean metal surface by employing the Keldysh-Green's functional theory. We reveal that the STM-IETS spectrum is proportional to the momentum-resolved Eliashberg function, and not solely to the phonon DOS. By ab initio calculations of the momentum-resolved Eliashberg function combined with the phonon dispersion, we assign the observed peak to the out-of-plane polarized surface phonon mode.