The premelting of ice is well known, but little is known about how the premelted and solid surfaces convert to each other. In this work, the transition dynamics between two phases are revealed with large-scale molecular dynamics simulations. Supercooling and superheating states exist in the transition, and are overcome by nucleation-like processes. The natural inhomogeneity of ice surfaces enhances nuclei formation, while it only accelerates premelting but not freezing. Furthermore, the complete freezing of ice surfaces may be hindered by the stacking order mismatch between nuclei. This work points out the importance of metastable states in premelting, and the necessity of a large system scale in describing its transition process.

We propose a mechanism for magnon-plasmon coupling and hybridization in ferromagnetic (FM) and antiferromagnetic (AFM) systems. The electric field associated with plasmon oscillations creates a nonequilibrium spin density via the inverse spin galvanic effect. This plasmon-induced spin density couples to magnons by an exchange interaction. The strength of magnon-plasmon coupling depends on the magnetoelectric susceptibility of the system and the wavevector at which the level repulsion has happened. This wavevector may be tuned by an applied magnetic field. In AFM systems, the degeneracy of two chiral magnons is broken in the presence of a magnetic field, and we find two separate hybrid modes for left-handed and right-handed AFM magnons. Furthermore, we show that magnon-plasmon coupling in AFM systems is enhanced because of strong intrasublattice spin dynamics. We argue that the recently discovered two-dimensional magnetic systems are ideal platforms to investigate proposed magnon-plasmon hybrid modes.

Intercalation with extra atoms between atomic layers provides a new dimension to engineer transition metal dichalcogenide materials which show diverse many-body phenomena, such as charge density wave (CDW) and superconductivity. Here, we report the quenched CDW of 33.3% Nb-intercalated bilayer ${\mathrm{NbSe}}_2$ synthesized by the molecular beam epitaxy method. Our first-principles calculation shows that the absence of CDW in this self-intercalated ultrathin film is attributed to the strong valence bond and charge transfer between intercalated Nb and ${\mathrm{NbSe}}_2$ layers. Moreover, the large in-plane upper critical field beyond the Pauli limit of this thin film has been revealed by scanning tunneling spectroscopy. These findings not only deepen the understanding of the CDW and superconductivity of transition metal dichalcogenides, but also show a different approach to control the many-body electronic states which are potentially used for future electronics.

A recent theoretical study has shown that hexagonal ${\mathrm{YCo}}_5$ is dynamically unstable and distorts into a stable orthorhombic structure. In this paper, we show theoretically that the orthorhombic phase is energetically more stable than the hexagonal phase in the low-temperature region, while the phonon entropy stabilizes the hexagonal phase thermodynamically in the high-temperature region. The orthorhombic-to-hexagonal phase transition temperature is $\sim 165$ K, which is determined using self-consistent phonon calculations. We investigate the magnetocrystalline anisotropy energy (MAE) using self-consistent and non-self-consistent (force theorem) calculations with spin-orbit interaction (SOI) along with the Hubbard $U$ correction. Then, we find that the orthorhombic phase has MAE, orbital moment, and orbital moment anisotropy values that are similar to those of the hexagonal phase when the self-consistent calculation with SOI is performed. Since the orthorhombic phase still gives magnetic properties comparable to those found in experiments, the orthorhombic distortion is potentially realized in the low-temperature region, which awaits experimental exploration.

We present a microscopic model, describing current-driven switching in metallic atomic-size contacts. Applying a high current through an atomic-size contact creates a strong electronic nonequilibrium that excites vibrational modes by virtue of the electron-vibration coupling. Using density-functional theory (DFT) in combination with the Landauer-Büttiker theory for phase-coherent transport, expressed in terms of nonequilibrium Green's functions (NEGFs), we study the current-induced forces arising from this nonequilibrium and determine those vibrational modes which couple most strongly to the electronic system. For single-atom lead (Pb) contacts we show specific candidates for bistable switches, consisting of two similar atomic configurations with differing electric conductance. We identify vibrational modes that induce a transition between these configurations. Our results reveal a possible origin of bistable switching in atomic-size contacts through excitation of vibrations by inelastic electron scattering and underline the power of the combined DFT-NEGF approach and statistical mechanics analysis of a Langevin equation to overcome the timescale gap between atomic motion and rare switching events, allowing for an efficient exploration of the contacts' configurational phase space.

We have developed a tensor network approach to the two-dimensional fully frustrated classical XY spin model on the kagome lattice, and clarified the nature of the possible phase transitions of various topological excitations. We find that the standard tensor network representation for the partition function does not work due to the strong frustrations in the low-temperature limit. To avoid the direct truncation of the Boltzmann weight, based on the duality transformation, we introduce a different representation to build the tensor network with local tensors lying on the centers of the elementary triangles of the kagome lattice. Then the partition function is expressed as a product of one-dimensional transfer matrix operators, whose eigenequation can be solved by the variational uniform matrix product state algorithm accurately. The singularity of the entanglement entropy for the one-dimensional quantum operator provides a stringent criterion for the possible phase transitions. Through a systematic numerical analysis of thermodynamic properties and correlation functions in the thermodynamic limit, we prove that the model exhibits a single Berezinskii-Kosterlitz-Thouless phase transition only, which is driven by the unbinding of $\frac{1}{3}$ fractional vortex-antivortex pairs determined at $T_c\simeq 0.075J_1$ accurately. The absence of long-range order of chirality or quasi-long-range order of integer vortices has been verified in the whole finite-temperature range. Thus, the long-standing controversy about the phase transitions in this fully frustrated XY model on the kagome lattice is solved rigorously, which provides a plausible way to understand the charge-$6e$ superconducting phase observed experimentally in the two-dimensional kagome superconductors.

We present an experimental study of bilayers of a disordered Ag metal layer close to the metal-insulator transition and an indium-oxide film which is on the insulating side of the superconductor insulator transition. Our results show that superconducting fluctuations within the indium-oxide film, that proximitize the underlying metal layer, induce insulating rather than superconducting behavior. This is ascribed to suppression of density of states (due to the superconducting energy gap) for quasiparticles in the proximitized regions. Our results present a manifestation of the proximity effect phenomenon and provide important insight into the nature of the insulating phase of the disorder driven superconductor insulator transition.

The exchange-correlation functional is at the core of density functional theory (DFT) and determines the accuracy of DFT in describing the interactions among electrons/ions in solids and molecules. The strongly constrained and appropriately normed functional (SCAN) and its derivatives, regularized SCAN (rSCAN) and regularized-restored SCAN (${\mathrm{r}}^2\mathrm{SCAN}$), are particularly promising due to their remarkable overall accuracy in the description of various properties while retaining a high computational efficiency as compared to hybrid functionals. However, an exhaustive assessment on the performance of these functionals in predicting the finite-temperature lattice constant of solids is still lacking. Here, we systematically study the room-temperature lattice constants of 60 cubic binary compounds within the quasiharmonic approximation using SCAN, rSCAN, ${\mathrm{r}}^2\mathrm{SCAN}$, local density approximation (LDA), and two common generalized gradient approximation (GGA) functionals, Perdew-Burke-Ernzerhof (PBE) and revised PBE for solid and surface (PBEsol). We found that SCAN exhibits numerical instabilities in free energy calculations, manifested by the presence of spurious imaginary frequencies in phonon dispersion relationships and poor fitting in Murnaghan's equation of state of Helmholtz free energy for 30 compounds. The revised SCAN functionals show much better numerical stabilities and reduce the number of the compounds with numerical issues to 22 and 9 for rSCAN and ${\mathrm{r}}^2\mathrm{SCAN}$, respectively. The mean relative absolute errors (MRAE) of the calculated lattice constants at room temperature for the remaining 30 binary compounds are 0.92%, 1.10%, 0.32%, 0.51%, 0.58%, and 0.67% for LDA, PBE, PBEsol, SCAN, rSCAN, and ${\mathrm{r}}^2\mathrm{SCAN}$, respectively. Furthermore, we found that the SCAN functional incorrectly predicts unstable phonon modes for a few compounds at their equilibrium volumes, which indicates the existence of a new ground state structure with lower energy than the cubic structure at 0 K, disagreeing with experiments. Our results provide a useful guide in choosing suitable functionals in describing anharmonic phonons and shed light on second-order force constant calculations that may help to develop more accurate exchange-correlation functionals for solids.

Using the master equation approach, we look for fingerprints of the interaction between the localized spin $S$ of a nanomagnet coupled to spin-polarized leads and its quantized vibrational modes. We find that the stationary and transient currents are sensitive to vibron-assisted transitions of the molecular spin on both sides of the anisotropy barrier. Such transitions are associated with vibron-dressed states and triggered under resonant conditions. Transport calculations are presented for two antiparallel configurations of the spin-polarized electrodes. In the first configuration, and far from a resonance point, a blockade is imposed on both the electronic and molecular spins via their exchange interaction. When sweeping the magnetic field through resonance, the spin-vibron interaction removes this blockade and allows the indirect reading of resonant transitions as the molecular spin climbs the left side of the anisotropy barrier. In the second configuration, the anisotropy barrier is overcome but the vibron-assisted transitions on the right side of the anisotropy barrier “delocalize” the molecular spin and do not allow the complete current-induced magnetic switching $-S\to S$. In both configurations, the stationary current increases on resonance, due to additional transport channels triggered by the spin-vibron coupling. Therefore, the switching of the spin-vibron coupling could be detected in future transport experiments.

We have performed ${}^{115}\mathrm{In}$-NMR spectroscopy for ${\mathrm{Ni}}_2{\mathrm{InSbO}}_6$ with corundum-related crystal structure to reveal magnetic structures that develop in high magnetic fields. At low fields ${\mathrm{Ni}}_2{\mathrm{InSbO}}_6$ shows a helical magnetic order with a long wavelength because of its chiral and polar crystal structure. The field-induced magnetic state was not investigated by microscopic experiment, because an extremely high magnetic field is required to modify the antiferromagnetically coupled helical structure. From the analysis of our ${}^{115}\mathrm{In}$-NMR spectra obtained at high magnetic fields, we confirm that the canted antiferromagnetic structure appears in fields applied in the [110] direction, and the propagation vector of magnetic helix is rotated toward the field direction for fields in the [001] direction. We discuss the effect of a magnetic field that modifies the magnetic structure of an antiferromagnetic chiral magnet.

Deterministic switching of perpendicularly magnetized systems using spin-orbit torque (SOT) usually requires an in-plane auxiliary magnetic field, which limits its practical applications. Here, an interfacial Dzyaloshinskii-Moriya interaction is introduced into perpendicularly magnetized synthetic antiferromagnetic (AFM) systems by changing the type of capping or underlayer in the [capping layer]/Co/[Pt/Ir/Pt spacer layer]/Co/[underlayer] synthetic AFM system. Field-free switching in the synthetic AFM system is observed in the cases of W, Ta, ${\mathrm{Ir}}_{22}{\mathrm{Mn}}_{78}$ capping layers or ${\mathrm{Ir}}_{22}{\mathrm{Mn}}_{78}$ underlayer. Among the synthetic AFM systems with field-free switching, the synthetic AFM system with ${\mathrm{Ir}}_{22}{\mathrm{Mn}}_{78}$ capping layer shows the largest dampinglike SOT efficiency, ${\xi }_{\mathrm{DL}}=28.1\%$. We also found observed large ${\xi }_{\mathrm{DL}}$ is related to the enhancement of spin absorption in antiferromagnetic Co magnetization configuration in synthetic AFM system compared to that in ferromagnetic Co magnetization configuration and the degree of enhancement increases with increasing the magnitude of interlayer exchange coupling between Co layers in synthetic AFM system. These results suggest that the synthetic AFM system is a promising building block for future nonvolatile high-speed memories and logic circuits using the spin Hall effect.

The observation of a sizable anomalous Hall effect in magnetic materials with vanishing magnetization has renewed interest in understanding and engineering this phenomenon. Antiferromagnetic antiperovskites are one of the emerging material classes that exhibit a variety of interesting properties owing to a complex electronic band structure and magnetic ordering. Reports on the anomalous Nernst effect and its magnitude in this class of materials are, however, very limited. This scarcity may be partly due to the experimental difficulty of reliably quantifying the anomalous Nernst coefficient. Here, we report experiments on the anomalous Nernst effect in antiferromagnetic antiperovskite ${\mathrm{Mn}}_3\mathrm{NiN}$ thin films. Measurement of both the anomalous Hall and Nernst effects using the same sample and measurement geometry makes it possible to directly compare these two effects and quantify the anomalous Nernst coefficient and conductivity in ${\mathrm{Mn}}_3\mathrm{NiN}$. We carefully evaluate the spatial distribution of the thermal gradient in the sample and use finite-element modeling to corroborate our experimental results.

Grazing incidence fast-atom diffraction (GIFAD) uses keV atoms to probe the topmost layer of crystalline surfaces. The atoms are scattered by the potential energy landscape of the surface onto elastic diffraction spots located at the Bragg angles and on the Laue circle. However, atoms transfer a significant momentum to the surface, giving rise to possible phonon excitation. This causes the inelastic intensity to spread above and below the circle along the direction of the surface normal. The relative intensity of the elastic contribution is well fitted by the Debye-Waller model adapted to GIFAD, but the composite azimuthal line profile governing the ability to resolve diffraction spots has not been investigated in detail. The paper reports a series of diffraction measurements of helium on a LiF(001) surface revealing marked differences in the polar ($\theta$) and lateral ($\varphi$) inelastic profiles but also similarities in the evolution of their line widths ${\sigma }_{\theta }$ and ${\sigma }_{\varphi }$. We observe two regimes: When elastic diffraction is significant, the Laue circle appears as a reference for inelastic diffraction; the azimuthal inelastic line shape is an exponential decay and its width increases almost linearly as the scattering angle deviates from the specular condition. When elastic diffraction weakens, the inelastic line shape evolves towards a Gaussian and its width is no longer minimum on the Laue circle. As a possible difference with x ray, neutrons, and electrons, the in-plane motion of surface atoms may not be the dominant cause of the broadening of the lateral profile in GIFAD.

Using the density-matrix formalism, we show that graphene nanomeshes (GNMs)—graphene sheets patterned with antidots—have large plasmon-enhanced nonlinear optical response. GNMs can be designed to behave as quasi-one-dimensional plasmonic crystals in which plasmons with large propagation lengths are efficiently excited. The associated third-order Kerr and third-harmonic-generation susceptibility can be as high as ${10}^{-7}$ and ${10}^{-9}{\mathrm{m}}^2{\mathrm{V}}^{-2}$, respectively, over the mid-to-near-infrared frequency range. Furthermore, carrier-density tuning in GNMs can flip the propagation direction of plasmonic waves and enables bidirectional switching of optical signals.

The relative strength of different proximity spin-orbit couplings in graphene on transition metal dichalcogenides (TMDCs) can be tuned via the metal composition in the TMDC layer. While ${\mathrm{Gr}/\mathrm{MoSe}}_2$ has a normal gap, proximity to ${\mathrm{WSe}}_2$ instead leads to valley-Zeeman-driven inverted bands. Although the ${\mathbb{Z}}_2$ index vanishes, these systems enable a concentration-dependent topological crossover with band gap closure when graphene is stacked on a composite or alloyed TMDC layer. This is due to a nonzero Berry curvature at the individual valleys, i.e., a hallmark of the quantum valley Hall effect and a change in the valley Chern index at a critical composition ratio. Therefore, inherently, we also expect that stacked heterostructures of graphene on composite TMDC layers should host localized boundary modes due to the presence of ${\mathrm{Gr}/\mathrm{WSe}}_2$- and ${\mathrm{Gr}/\mathrm{MoSe}}_2$-like domains with opposite valley Chern indices. In this study, we show that a Gr/(Mo-$\mathrm{W}){\mathrm{Se}}_2$ heterostructure with a lateral interface in the TMDC layer can indeed host valley-dependent topologically protected in-gap propagating modes, similar to those at the border of commensurate AB and BA domains in biased minimally-twisted bilayer graphene. However, the stability of these modes depends crucially on the system size. We demonstrate that the electronic behavior of Gr/(Mo-$\mathrm{W}){\mathrm{Se}}_2$ heterostructures evolves from a homogeneous effective medium to a superposition of domain-localized bands and zero-energy branch crossings as the domain size in the alloyed TMDC layer is increased.

The temperature-dependent behavior of magnetic domains plays an essential role in the magnetic properties of materials, leading to widespread applications. However, experimental methods to access the three-dimensional (3D) magnetic domain structures are very limited, especially for antiferromagnets. Over the past decades, the spin-orbit Mott insulator iridate ${\mathrm{Sr}}_2\mathrm{Ir}{\mathrm{O}}_4$ has attracted particular attention because of its interesting magnetic structure and analogy to superconducting cuprates. Here, we apply resonant x-ray magnetic Bragg coherent diffraction imaging to track the real-space 3D evolution of antiferromagnetic ordering inside a ${\mathrm{Sr}}_2\mathrm{Ir}{\mathrm{O}}_4$ single crystal as a function of temperature, finding that the antiferromagnetic domain shows anisotropic changes. The anisotropy of the domain shape reveals the underlying anisotropy of the antiferromagnetic coupling strength within ${\mathrm{Sr}}_2\mathrm{Ir}{\mathrm{O}}_4$. These results demonstrate the high potential significance of 3D domain imaging in magnetism research.