The 50 most-cited articles in Journal of the Physical Society of Japan, 2024

We overview recent developments of electronic orderings and associated cross correlations in condensed matter physics based on a complete set of multipole representations (electric, magnetic, electric toroidal, and magnetic toroidal multipoles) with distinct space-time inversion symmetries. By means of the symmetry-adapted complete basis set in any physical Hilbert space including atomic and cluster degrees of freedom, it provides a unified description of electronic orderings, deformations of band structures, cross correlations, and transport properties in solids. We review that a multipole representation is a powerful tool to attain a comprehensive understanding of various electronic properties and physical phenomena observed in materials. We also demonstrate how to identify active multipoles and expected physical phenomena in real materials with several examples. Our review would serve as a solid foundation for future studies toward observations and identifications of unknown electronic phases and their related physical phenomena.

We report a $^{139}$La-NMR study of polycrystalline samples of multi($n$)-layered nickelates, La$_3$Ni$_2$O$_{7-δ}$ ($n=2$) and La$_4$Ni$_3$O$_{10-δ}$ ($n=3$), at ambient pressure. Measurements of the nuclear magnetic resonance (NMR) spectra and nuclear spin relaxation rate ($1/T_1$) indicate the emergence of a density wave order with a gap below $T^*\sim150$ K for La$_3$Ni$_2$O$_{7-δ}$ and $\sim130$ K for La$_4$Ni$_3$O$_{10-δ}$. The finite value of $1/T_1$ below $T^*$ indicates metallic ground states with the remaining density of states at the Fermi level ($E_{\rm F}$) under the density wave order. These features are attributed to multiple $d$ electron bands with different characteristics. Above $T^*$, the gradual decrease in $1/T_1T$ upon cooling implies the presence of a band with flat dispersion near $E_{\rm F}$. From our microscopic probes, we point out that these nickelates ($n=2$ and $3$) possess similar electronic states despite the difference in the formal valence of the Ni-$d$ electron states, which provides a basis for understanding the novel high-$T_{\rm c}$…

We theoretically study the tunneling conductance of a junction consisting of a two-dimensional unconventional $p$-wave magnet (UPM) and a superconductor (SC) for various pairing symmetries. The zero bias conductance peaks arising from the dispersionless surface Andreev bound states (SABSs) in $d_{xy}$-wave and $p_{x}$-wave superconductor junctions are insensitive against varying the magnetic spin-splitting strength $α_{y}$. Moreover, for chiral $p$- or chiral $d$-wave SCs, zero bias conductance shows a non-monotonic change as a function of $α_{y}$ indicating the existence of the dispersive SABSs. Our obtained results of tunneling spectroscopy based on a UPM serve as an effective way for the identification of the pairing symmetries of unconventional superconductors. It is noted that our used Hamiltonian of UPM is also available for persistent spin helix systems.

This review describes recent significant research developments made on the layered perovskite Sr2RuO4 and discusses current issues from both experimental and theoretical perspectives. Since the discovery of superconductivity in Sr2RuO4 in 1994, studies using high-quality single crystals quickly revealed it to be an archetypal unconventional superconductor among strongly correlated electron systems. In particular, it was thought that the spin-triplet chiral p-wave superconducting state, which breaks time-reversal symmetry, was a prominent possibility. In 2019, however, a new development overturned the past experimental results, and spin-singlet-like behavior became conclusive. Furthermore, innovation in uniaxial strain devices has stimulated researchers to explore changes in the superconducting state by controlling the symmetry and dimensionality of the Fermi surfaces and enhancing the superconducting transition temperature Tc from 1.5 to 3.5 K. A spin-singlet chiral d-wave superconducting state is consistent with most of these recent experimental results. Nevertheless, there are…

The fundamental idea of the excitonic insulator (EI) driven by electron-hole correlations in narrow-gap semiconductors or semimetals was originally proposed in the 1960s, and only theoretical studies had been advanced for a long time. However, the rise of new candidate materials and recent developments in measurement techniques have enabled us to discuss the possibilities of EI states in real materials experimentally. In this article, we review recent progress in the research of EIs. We start with an introduction to the theoretical background of the EI and the mechanism of the order formation including its relation to the physics of the Bardeen-Cooper-Schrieffer (BCS) - Bose-Einstein condensation (BEC) crossover. We also review the EI states studied in the context of strongly correlated electron systems. Then, we introduce the candidate materials for the EI and the issues raised by recent experiments. For example, the phase transitions in several candidate materials are accompanied by lattice distortions, and the contributions from electron-lattice coupling hinder the identification…

Magnetic skyrmions are particle-like spin-swirling objects ubiquitously realized in magnets. They are topologically stable chiral kinks composed of multiple modulation waves of spiral spin structures, where the helicity of each spiral is usually selected by antisymmetric exchange interactions in noncentrosymmetric crystals. We report an experimental observation of a distorted triangular lattice of skyrmions in the polar tetragonal magnet EuNiGe$_3$, reflecting a strong coupling with the lattice. Moreover, through resonant x-ray diffraction, we find that the magnetic helicity of the original spiral at zero field is reversed when the skyrmion lattice is formed in a magnetic field. This means that the energy gain provided by the skyrmion lattice formation is larger than the antisymmetric exchange interaction. Our findings will lead us to a further understanding of emergent magnetic states.

We successfully synthesized samples of La$_{3}$Ni$_{2}$O$_{7+δ}$ ($δ= -0.50$, $-0.16$, $0.00$, $+0.01$, and $+0.12$) and measured the resistance under extremely high pressures using a diamond anvil cell to establish the electronic phase diagram. A Mott insulating state appears at $δ= -0.50$, where all Ni ions are divalent. With increasing oxygen content, superconductivity appears at $δ= 0.00$ and higher, above approximately 25 GPa, passing through Anderson localization at $δ= -0.16$. The superconducting transition temperature $T_{\mathrm{c}}$ decreases with increasing pressures for both $δ= 0.00$ and $+0.12$, with the pressure dependence of $T_{\mathrm{c}}$ being much stronger in the latter than in the former.

Various single crystal growth techniques are presented for the unconventional superconductor UTe2. The molten salt flux liquid transport (MSFLT) method is employed to grow high-quality and large single crystals, exhibiting a high residual resistivity ratio (RRR = 200-800). On the other hand, the Te self-flux and chemical vapor transport (CVT) method produces samples of lower quality. The MSFLT method is a hybrid approach that combines the molten salt flux (MSF) and CVT methods. One significant advantage is that the materials gradually crystallize at the relatively low temperature which is fixed during the main process. This might be crucial for preventing U deficiency and obtaining high-quality and large single crystals of UTe2. Many different single crystals obtained by different technique were characterized by resistivity, specific heat measurements. The superconducting transition temperature decreases with the residual resistivity, followed by the Abrikosov-Gor'kov pair breaking theory. The highest quality sample reaches Tc=2.1K. The residual gamma-value of specific heat for the…

In this study, we first observed second-order primary rogue waves in solids by experiments using a modal based on primary waves. We found that the propagation of primary waves in solids can be described by the nonlinear Schrödinger equation. To enhance our understanding, we employed variational mode decomposition and identified the inherent frequency as the main factor. Therefore, we conducted spectral analysis to determine the frequency and discussed the results. The theoretical and experimental results are found to be in agreement, and our findings can be applied to the non destructive testing of large engineering structures.

The superconducting transition temperatures, $T_{\mathrm{c}}$, of La$_{4}$Ni$_{3}$O$_{10+δ}$($δ$ = 0.04 and -0.01) were determined under various pressures up to 124.9 GPa by electrical resistance measurements with a diamond anvil cell. $T_{\mathrm{c}}$ exhibits a strong dependence on oxygen content within the pressure range of approximately 20 GPa and 80 GPa. At 48.0 GPa, $T_{\mathrm{c}}$ of La$_{4}$Ni$_{3}$O$_{10.04}$ peaks at 36 K, marking the highest $T_{\mathrm{c}}$ reported thus far.

Obtaining structural information has always been of primary importance in condensed matter physics, chemistry, and materials science. To refine crystal and magnetic structures, neutron powder diffraction is widely employed owing to comparable scattering cross-sections of neutrons for nuclear and magnetic scattering. The neutron powder diffractometer HERMES stationed at the Japan Research Reactor has served for structural studies, and modifications and improvements were made after the Great East Japan Earthquake. We here present an overview of the upgraded instrument focusing on newly equipped components and the latest developments in data reduction, which all took place during the suspension of the reactor operation for nearly a decade.

We report the magnetoresistance of high-quality single crystals of UTe2 with Tc=2.1K in high magnetic fields up to 36T, with the field direction between the b and c-axes. From the angular dependence of the upper critical field Hc2, we found that the field-reentrant superconducting phase near H // b-axis extends up to a field angle (24 deg) from the b to c-axis, where another field-reentrant superconducting phase begins to appear above the metamagnetic transition field, Hm. Our results suggest that the field-reentrant superconductivity below Hm near the b-axis is closely related to the superconductivity above Hm when the field is tilted toward the c-axis. Superconductivity appears to be robust when the field direction is maintained perpendicular to the magnetization easy axis, implying that fluctuations boosting superconductivity may persist. At first glance, these findings resemble the field-reentrant (reinforced) superconductivity observed in ferromagnetic superconductors URhGe and UCoGe, where Ising-type ferromagnetic fluctuations play a crucial role. However, in UTe2, the…

Chiral phonons with atomic rotations converted into electron spins result in a change of spin magnetizations in crystals. In this paper, we investigate a new conversion of chiral phonons into magnons both in ferromagnets and antiferromagnets by spin models with exchange and Dzyaloshinskii-Moriya interactions. The atomic rotations in chiral phonons are treated as slow phonons, which modulate spin-spin interaction and induce time-dependent magnon excitations due to geometric effect within adiabatic approximation. We demonstrate that a non-trivial change of the number of magnons requires breaking of the spin-rotation symmetry around the spin quantization axis. As a result, the clockwise and counterclockwise chiral phonons induce a change of the magnon number with opposite signs, which corresponds to an increasing or decreasing spin magnetizaton due to the chiral nature of the atomic rotations. In particular, in antiferromagnets, the modulation of magnons due to chiral phonons generates a non-zero net magnetization by the proposed effect, which is expect to be observed in experiments.

We report the re-measurement of the $a$-axis spin susceptibility component in an early-stage sample of the spin-triplet superconductor UTe$_2$ with the transition temperature of $T_{\rm SC}$ = 1.6 K. Using Knight-shift measurements along the $b$ axis and at a 10-degree tilt from the $b$ axis towards the $a$ axis, we accurately determined the $a$-axis component without directly measuring the $a$-axis Knight shift. Our results reveal a decrease of approximately 3\% in the $a$-axis spin susceptibility in the superconducting state under $a$-axis magnetic field $μ_0 H_a \sim 0.1$ T, indicating that the spin susceptibility decreases similarly in both early-stage and ultraclean samples with $T_{\rm SC}$ = 2.1 K. The previously reported absence of the reduction in Knight shift is attributed to the missing of signal from the superconducting region and to the detection of residual signals from the non-superconducting region instead. We also found that the decrease in the $a$-axis spin susceptibility is immediately suppressed with increasing the $a$-axis magnetic field and is estimated to be…

In correlated compounds containing cations in high formal oxidation states (assigned by assuming that anions attain full valence shells), the energy of ligand to cation charge transfer can become small or even negative. This yields compounds with a high degree of covalence and can lead to a self-doping of holes into the ligand states of the valence band. Such compounds are of particular topical interest, as highly studied perovskite oxides containing trivalent nickel or tetravalent iron are negative charge transfer systems, as are nickel-containing lithium ion battery cathode materials. In this report, we review the topic of negative charge transfer energy, with an emphasis on plots and diagrams as analysis tools, in the spirit of the celebrated Tanabe-Sugano diagrams which are the focus of this Special Topics Issue.

We develop a microscopic theory for the spin Seebeck effect (SSE) in Néel and canted phases of antiferromagnetic insulators. We calculate the DC spin current tunneling from the antiferromagnet to an attached metal, incorporating the spin-wave theory and the non-equilibrium Green's function approach. Our result shows a sign change of the spin current at the spin-flop phase transition between Néel and canted phases, which is in agreement with a recent experiment for the SSE of $\rm Cr_2O_3$ in a semi-quantitative level. The sign change can be interpreted from the argument based on the density of states of up- and down-spin magnons, which is related to the polarized-neutron scattering spectra. The theory also demonstrates that the spin current in the Néel phase is governed by the magnon correlation, while that in the canted phase consists of two parts: Contributions from not only the magnon dynamics but also the static transverse magnetization. This result leads to a prediction that at sufficiently low temperatures, the spin current non-monotonically changes as a function of magnetic…

We investigate the Hubbard model with the Rashba spin-orbit coupling on a square lattice. The Rashba spin-orbit coupling generates two-dimensional Weyl points in the band dispersion. In a system with edges along [11] direction, zero-energy edge states appear, while no edge state exists for a system with edges along an axis direction. The zero-energy edge states with a certain momentum along the edges are predominantly in the up-spin state on the right edge, while they are predominantly in the down-spin state on the left edge. Thus, the zero-energy edge states are helical. By using a variational Monte Carlo method for finite Coulomb interaction cases, we find that the Weyl points can move toward the Fermi level by the correlation effects. We also investigate the magnetism of the model by the Hartree-Fock approximation and discuss weak magnetic order in the weak-coupling region.

A new multiplex-type inelastic neutron scattering spectrometer, HOrizontally Defocusing Analyzer Concurrent data Acquisition spectrometer (HODACA), was recently developed and built at the C1-1 cold neutron beam port in JRR-3. The spectrometer is suitable for dynamics measurements in the energy range of $-1$ meV $\lesssim \hbar ω\lesssim$ 7 meV, catering to a broad array of research fields in physics and material science. HODACA combines 24 detectors and 132 pieces of analyzer crystals and has an estimated measurement efficiency that is 70 times greater than the existing conventional triple-axis spectrometer at the C1-1 beam port. The concept, design, specification, and results of commissioning experiments are described.

We analyze the condition of photo-induced atomic-scale chirality and magnetic toroidal moment. By performing a high-frequency expansion in the Floquet formalism, we derive an effective static model Hamiltonian from the spinful $s$-$p$ hybridized model of a single atom interacting with an electromagnetic wave with a particular polarization. The lowest-order and third-order contributions in the high-frequency expansion give rise to the coupling to induce an electric toroidal monopole corresponding to microscopic chirality, while the second-order contribution provides the coupling to induce a magnetic toroidal dipole. We also discuss the condition of the polarization of the electromagnetic wave and induced multipoles. Our results stimulate a new direction of controlling unconventional multipoles by electromagnetic waves.

The various magnetic orders observed in approximant crystals of Tsai-type quasicrystal are important for deepening our understanding of mysterious magnetism in quasicrystals. Using an icosahedral cluster model with inter-cluster interactions, we give an intuitive explanation of the mechanism of magnetic orders previously reported by classical Monte-Carlo simulations for an approximant-crystal model describing a Gd-based Tsai-type 1/1 approximant crystal.

The large anomalous Hall effect (AHE) in antiferromagnetic (AF) materials arises from symmetry breaking equivalent to a ferromagnetic (FM) state. Consequently, this suggests that the observed AHE is induced by the intrinsic mechanism of the band structure effect, which in turn induces dissipationless transverse conductivity. Confirmation of impurity-insensitive anomalous Hall conductivity (AHC) is crucial to conclude this interpretation; however, experimental investigations in AF materials are limited by the lack of high quality systems. In this study, we show that the AF material NbMnP, which exhibits a large AHE, offers a high quality single crystal. Our findings clearly revealed that the large AHC and the tiny net magnetization of $\sim10^{-3} μ_{\mathrm{B}}$/Mn are inherent in this material, irrespective of disorder. NbMnP is a novel AF material that generates FM responses in the regime where there is less impurity scattering.

We propose a model to describe the fluctuations in the internal magnetic field due to ion dynamics observed in the muon spin relaxation ($μ$SR) by an Edwards-Anderson type autocorrelation function that separates the quasi-static and dynamic components of the correlation by a parameter $Q$ (where $0\le Q\le1$). Our Monte Carlo simulations for this model showed that the time evolution of muon spin polarization deviates significantly from the Kubo-Toyabe (KT) function. To further validate the model, the results of simulations were compared with the $μ$SR spectra observed in a hybrid organic-inorganic perovskite FAPbI$_3$ [with FA referring to HC(NH$_2)_2$], where local field fluctuations associated with the rotational motion of FA molecules and quasi-static fields from the PbI$_3$ lattice are presumed to coexist. The least-squares curve fitting showed reasonable agreement with the model with $Q=0.947(3)$, and the fluctuation frequency of the dynamical component was obtained. This result opens the door to the possibility of experimentally distinguishing fluctuations due to dynamics of…

The charge loop current (cLC) state has attracted increasing attention in kagome metals. Here, we calculate the spontaneous currents along the nearest sites $i$ and $j$, $J_{i,j}$, induced by the cLC order that is the imaginary and odd-parity hopping integral modulation $δt_{i,j}$. We reveal that the magnitude of $J_{i,j}$ strongly depends on the nearest sites $i$ and $j$ in the $2\times2$ cLC state, where $η\equiv |δt_{i,j}|$ is equivalent for all nearest sites. The obtained $J_{i,j}$ becomes large near the van-Hove singularity (vHS) filling ($n\sim n_{vHS}$) even when $η$ is fixed. Interestingly, the obtained $J_{i,j}$ exhibits the logarithmic divergence behavior at low temperatures for $n\sim n_{vHS}$ with a fixed $η$, by reflecting the vHS points that are the characteristic of kagome metals. The present study provides useful information for local electronic state measurements, such as the site-selective NMR and STM experiments.

We derive a quantum spin Hamiltonian of the spin-1/2 zigzag chain realized in a rare earth ytterbium-based magnetic insulator, YbCuS2. This material undergoes a transition at 0.95K to an incommensurate magnetic phase with small moments, which does not conform to the nonmagnetic singlet ground state of the spin-1/2 Heisenberg model. We take account of octahedral crystal field effect, atomic spin-orbit coupling, and strong Coulomb interactions on Yb ions, and perform a four-order perturbation theory to evaluate the superexchange coupling constants. A small but finite anisotropic exchange coupling called Γ-term appears similarly to the case reported previously in other triangular-based magnets. By varying several material parameters, we figure out two important factors to enhance Γ-term. One is the splitting of excited f-states with two holes, which efficiently selects the perturbation terms associated with the lowest excited state having large total angular momentum, and accordingly with high spatial anisotropy. The other is the tilting of octahedra or distortion of S-Yb-S bond angle,…

We investigate the ground state of a spin-1/2 kagome antiferromagnet at the 1/9 magnetization plateau, focusing primarily on six types of valence bond crystal (VBC) distortions. Among six types of VBC distortions, type 1 consistently exhibits the lowest ground-state energy. Analysis of the second derivative of the energy with respect to the distortion strength $J_{\rm d}$ using exact diagonalization reveals that, as the system size approaches the thermodynamic limit, the type 1 VBC state remains stable down to $J_{\rm d} = 1$, corresponding to the undistorted kagome lattice. Perturbation theory further supports the stability of the type 1 VBC state, providing energy values that agree with exact diagonalization results within 3%. We also explore the possibility that other types of VBC distortions could become the ground state, but type 1 VBC still exhibited the lowest energy. These findings suggest that the ground state of the 1/9 plateau in the kagome lattice is the type 1 VBC state.

\lco{} is known for its two-step spin crossover as a function of temperature. Despite efforts spanning over half a century, the origin of this phenomenon is still debated, particularly regarding how the microscopic spin states are involved in the observed macroscopic two-step spin crossover. High magnetic field studies on LaCoO$_{3}$ are performed because the magnetic field-induced spin crossover is induced, where the magnetic excited states become more stable in high magnetic fields than the non-magnetic ground states. This review focuses on the findings in LaCoO$_{3}$ at high magnetic fields over the last decade. A complex phase diagram has been revealed at high magnetic fields instead of solving the conventional problem of LaCoO$_{3}$. It suggests that appreciable spin state correlations are in play in LaCoO$_{3}$. The possibility of exciton condensation is also discussed.

Clarifying similarities and differences in physical properties between crystalline and quasicrystalline systems is one of central issues in studying quasicrystals. To contribute to this, we apply multifractal and hyperuniform analyses to nonuniform spatial patterns in the Bose-Hubbard model on the Penrose and Ammann-Beenker tilings. Based on the mean-field approximation, we obtain real-space distributions of local superfluid amplitude and boson density. In both Mott insulating and superfluid phases, the distributions are hyperuniform. Analyzing the order metric that quantifies the complexity of nonuniform spatial patterns, we find that both quasicrystals show a significant increase of the order metric at a phase boundary between the Mott insulating and superfluid phases, in stark contrast to the case of a periodic square lattice. Our results suggest that hyperuniformity is a useful concept to differentiate between crystalline and quasicrystalline bosonic systems. The order metric clarifies if the distribution of a physical quantity reflects the point distribution or not, and…

We propose a method to perform a configuration determination for chiral and/or polar crystals by utilizing anisotropy of NMR shift. The chirality (handedness) or polarity of a crystal, that is characterized by its sign, can be extracted from the asymmetric magnetic-field angle dependence of NMR shift in the appropriate plane, as the configuration is reflected in the off-diagonal components of the shift tensor. This method is applicable to the triclinic, monoclinic, and trigonal crystal structures among 230 crystallographic space groups, and the appropriate planes to extract the asymmetric field-angle dependence are tabulated for all relevant space groups. We discuss how to determine the appropriate plane, and to identify each contribution of twin domains, and so on, by using the specific examples of Te, IrSn$_{4}$ and RhSn$_{4}$, and the spontaneous symmetry-breaking phases of URhSn. We also argue that an absolute-configuration determination is also possible in accordance with the relation between chirality or polarity of crystal and the sign of the relevant off-diagonal component…

Neutron scattering is a powerful tool to study magnetic structures and cross-correlated phenomena originated from symmetry of the magnetic structures in matter. Among a number of neutron scattering techniques, polarized neutron scattering is quite sensitive to the orientations of the magnetic moments, which are essential to understand microscopic mechanisms of the spin-driven emergent phenomena. Here, we present POlarized Neutron Triple-Axis spectrometer PONTA in the Japan Research Reactor 3 (JRR-3), and show the present capabilities of polarized and unpolarized neutron scattering by introducing recent results from the instrument.

We explore the pairing state and gap structure of UTe$_2$ using a six-orbital model which we call the $f$-$d$-$p$ model. Our model accurately reproduces the quasi-two-dimensional Fermi surfaces consistent with recent de Haas-van Alphen oscillation measurements and the $(0, \pm π, 0)$ antiferromagnetic spin fluctuations observed by neutron scattering. We incorporate on-site Coulomb repulsion for $f$ electrons and solve the linearized Eliashberg equation within the third-order perturbation theory to investigate the superconducting symmetry in UTe$_2$. The most likely state is found to be an $s$-wave state with a highly anisotropic superconducting gap structure that exhibits a point-node-like behavior of the specific heat at low temperatures.

The demand for classical-quantum hybrid algorithms to solve large-scale combinatorial optimization problems using quantum annealing (QA) has increased. One approach involves obtaining an approximate solution using classical algorithms and refining it using QA. In previous studies, such variables were determined using molecular dynamics (MD) as a continuous optimization method. We propose a method that uses the simple continuous relaxation technique called linear programming (LP) relaxation. Our method demonstrated superiority through comparative experiments with the minimum vertex cover problem versus the previous MD-based approach. Furthermore, the hybrid approach of LP relaxation and simulated annealing showed advantages in accuracy and speed compared to solving with simulated annealing alone.

The storage capacity of a binary classification model is the maximum number of random input-output pairs per parameter that the model can learn. It is one of the indicators of the expressive power of machine learning models and is important for comparing the performance of various models. In this study, we analyze the structure of the solution space and the storage capacity of fully connected two-layer neural networks with general activation functions using the replica method from statistical physics. Our results demonstrate that the storage capacity per parameter remains finite even with infinite width and that the weights of the network exhibit negative correlations, leading to a 'division of labor'. In addition, we find that increasing the dataset size triggers a phase transition at a certain transition point where the permutation symmetry of weights is broken, resulting in the solution space splitting into disjoint regions. We identify the dependence of this transition point and the storage capacity on the choice of activation function. These findings contribute to understanding…

This paper reviews recent experimental and theoretical developments of the dynamic Jahn-Teller effect-driven phenomena in heavy transition metal-based spin-orbit Mott insulators. In cubic $4d/5d$ transition metal compounds, the spin, orbital, and lattice degrees of freedom can form quantum entanglement on metal sites and induce unconventional quantum phenomena. Fingerprints of orbital-lattice entanglement called the dynamic Jahn-Teller effect appear in spectroscopic data such as resonant inelastic x-ray scattering spectra. In cubic $5d^1$ compounds with the fcc structure, the dynamic Jahn-Teller states on metal sites behave cooperatively and exhibit rich ordered phases.

Machine learning and deep learning have revolutionized computational physics, particularly the simulation of complex systems. Equivariance is essential for simulating physical systems because it imposes a strong inductive bias on the probability distribution described by a machine learning model. However, imposing symmetry on the model can sometimes lead to poor acceptance rates in self-learning Monte Carlo (SLMC). Here, we introduce a symmetry equivariant attention mechanism for SLMC, which can be systematically improved. We evaluate our architecture on a spin-fermion model (\textit{i.e.}, double exchange model) on a two-dimensional lattice. Our results show that the proposed method overcomes the poor acceptance rates of linear models and exhibits a similar scaling law to large language models, with model quality monotonically increasing with the number of layers. Our work paves the way for the development of more accurate and efficient Monte Carlo algorithms with machine learning for simulating complex physical systems.

We report the magnetoelectric and optical properties of PbMn2Ni6Te3O18, a hexagonal collinear antiferromagnet with ferroaxial-type structural rotation. In the antiferromagnetic phase, we observe that the electric polarization (P) in the ab plane is linearly induced by a magnetic field applied in the ab plane but perpendicular to P, indicating the existence of off-diagonal linear magnetoelectricity. Furthermore, we observe the nonreciprocal directional dichroism for unpolarized light propagating along the c axis. These results indicate that PbMn2Ni6Te3O18 is a ferrotoroidic material with the c-axis toroidal moment which is induced by the combination of ferroaxial-type structural rotation and falsely chiral antiferromagnetism.

We report the temperature-pressure phase diagram of a UTe$_2$ single crystal that does not undergo a bulk superconducting transition but shows filamentary superconductivity with a critical transition temperature of 1 K at ambient pressure. Electrical-resistivity measurements reveal that the evolution of the filamentary superconducting state under pressure resembles the behavior observed in previous reports on bulk superconducting samples. AC calorimetry, however, does not show evidence for either bulk superconductivity or magnetism for pressures up to 1.6 GPa. Our results highlight the role of inhomogeneity in chemical-vapor-transport-grown UTe$_2$ samples and serve as a cautionary tale when probing electrical resistivity alone.

Layered material $β$-IrSn$_4$ ($I4_1/acd$, $D^{20}_{4h}$, #142), whose electron bands have symmetry-enforced Dirac points, was investigated using high-quality single crystals. It exhibits a pronounced linear field-dependence of magnetoresistance (LMR), which cannot be explained by currently existing models. Structures in the field-angle dependence of magnetoresistance and Hall resistivity are attributable to the Fermi surface topology; the presence of open orbits is inferred. At the superconducting (SC) transition, the specific-heat jump exhibits a significant increase in applied fields, revealing the type-I SC nature. This feature is attributable to the high Fermi velocity of linearly dispersive multibands. To clarify the mechanism of the puzzling LMR, investigations into the topological nature of those multibands in applied fields are highly desired.

We use the Profile numerical method to calculate the spectral line width, or half width at half maximum (HWHM) of the absorption peaks of multi-photon absorption processes in a two-dimensional graphene system (2DGS) according to important external parameters such as magnetic field and temperature in the presence of strong electromagnetic waves (SEMW). The appearance of these absorption peaks is theoretically obtained from magneto-phonon resonance conditions within the framework of the quantum kinetic equation. The results take into account both scattering mechanisms: electron-optical phonon and electron-acoustic phonon. Under the influence of the magnetic field, according to the increasing photon energy of the SEMW, the graph showing the dependence of the multi-photon nonlinear absorption coefficient on photon energy has the form of absorption spectrum lines following magneto-phonon resonance conditions. When increasing the value of the external magnetic field and the intensity of the SEMW, the intensity of the resonance peaks increases. In addition, the HWHM W of the resonance…

In this work, we show several types of (semi)-rational solutions for the two dimensional Mel'nikov equation. We derive multi-breather wave solutions. They present the oblique breathers, homoclinic orbits and their mixtures under two parameter constraints. We also obtain the general high-order lump solutions by employing the Schur polynomials. When internal parameters a2m+1 are large, the patterns display the polygons containing lower-order lump pattern in the central region together with possible multiple fundamental lumps in the outer region. When time t is large, two types of lump patterns are presented by considering the prediction solutions. The first type of lump patterns contain fundamental lumps with triangular shapes. The second type of lump patterns contain fundamental lumps with non-triangular shapes in the outer region, together with possible fundamental lumps with triangular shapes in the inner region. Furthermore, we construct the semi-rational solutions to exhibit the fascinating processes of fusion and fission between lumps and line solitons. These solutions should be…

With the evolution of numerical methods, we are now aiming at not only qualitative understanding but also quantitative prediction and design of quantum many-body phenomena. As a novel numerical approach, machine learning techniques have been introduced in 2017 to analyze quantum many-body problems. Since then, proposed various novel approaches have opened a new era, in which challenging and fundamental problems in physics can be solved by machine learning methods. Especially, quantitative and accurate estimates of material-dependent physical properties of strongly correlated matter have now become realized by combining first-principles calculations with highly accurate quantum many-body solvers developed with the help of machine learning methods. Thus developed quantitative description of electron correlations will constitute a key element of materials science in the next generation.

Kagome superconductors AV3Sb5 (A = K, Rb, and Cs) have attracted considerable attention due to their intriguing combination of unique electron correlations and nontrivial band topology. The interplay of these fundamental aspects gives rise to a diverse array of exotic electronic phenomena, including superconductivity and charge density wave (CDW) states. In this review, we present recent advancements in the study of the electronic band structure of AV3Sb5 using angle-resolved photoemission spectroscopy (ARPES), including the identification of the multiple van Hove singularities near the Fermi level and their close relationship with the CDW transition, spectroscopic features related to CDW-induced symmetry breakings, as well as direct observations of nodeless superconducting gaps and moderate electron-phonon couplings through ultrahigh-resolution ARPES, providing critical insights into the origins of CDW order and electron pairing symmetry. By synthesizing these key ARPES findings, this review aims to deepen our understanding of kagome-related physics.

Modulation of magnetization in magnetic Weyl semimetals leads to the shift of Weyl points in momentum space, which effectively serves as the chirality-dependent gauge field for the Weyl fermions. Here, we theoretically study such a magnetization-induced chiral gauge field, in a fully spin-polarized Weyl ferromagnet $\rm{Co}_3\rm{Sn}_2\rm{S}_2$. From a tight-binding model of $\rm{Co}_3\rm{Sn}_2\rm{S}_2$ on stacked kagome lattice with magnetism, we calculate the magnetization-dependent evolution of the Weyl points in momentum space, resulting in the chiral gauge field. In the presence of the magnetic domain wall structure, we evaluate the chiral magnetic field arising from the spatial profile of the chiral gauge field. We find that a magnetic domain wall in $\rm{Co}_3\rm{Sn}_2\rm{S}_2$ gives rise to a giant chiral magnetic field for the Weyl fermions, which reaches the order of a few hundred tesla to induce the Landau quantization. Such a giant chiral magnetic field may also influence the novel transport phenomena, such as the charge pumping by the domain wall motion, compatible with…