${\mathrm{Ni}}_3{\mathrm{TeO}}_6$ is a polar magnet with a pronounced magnetoelectric (ME) effect under high magnetic fields ($\approx 9\mathrm{T}$). Substitution of Ni with Co in ${\mathrm{Ni}}_3{\mathrm{TeO}}_6$ modulates the magnetic structure and reduces the critical field required to induce the ME response. In this study, we have grown single crystals of ${\mathrm{NiCo}}_2{\mathrm{TeO}}_6$ and measured the magnetic, dielectric, and magnetostriction properties. In addition, the temperature- and magnetic-field dependence of the dynamic ME coefficient (${\alpha }_{\mathrm{E}}=\mathrm{d}E/\mathrm{d}H$) was measured, enabling the construction of comprehensive ME phase diagrams. Pronounced peaks and dips in ${\alpha }_{\mathrm{E}}$ are observed at magnetic phase boundaries induced by temperature or magnetic field. Notably, the maximum ${\alpha }_{\mathrm{E}}$ is observed near the vicinity of the Néel temperature ($T_{\mathrm{N}}$) at a low magnetic field ($\approx 1.5\mathrm{T}$), in stark contrast with the high-field requirement in parent ${\mathrm{Ni}}_3{\mathrm{TeO}}_6$. Combined analysis of ${\alpha }_{\mathrm{E}}$ and magnetostriction data reveals that the anisotropic ME effect arises from the coexistence of spin-induced and magnetostriction-mediated polarization changes. These findings elucidate the intricate interplay among spin order, lattice strain, and electric polarization in ${\mathrm{NiCo}}_2{\mathrm{TeO}}_6$. Moreover, the combination of the dynamic ME coefficient and magnetostriction measurements provides a robust experimental framework for disentangling the microscopic origins of the ME effects.

Ab initio molecular dynamics (AIMD) refers to the solution of Newton's equations of motion for ions with forces ${\mathbf{f}}_i=-\partial E/\partial {\mathbf{R}}_i$ calculated from self-consistent electronic structure calculations. So-called machine-learning force field (ML-FF) schemes parametrize the potential energy surface very efficiently and make it possible to extend the time scale of AIMD simulations by orders of magnitude. The Landau-Lifshitz equation describes the dynamics of atomic magnetic moments ${\mathbf{m}}_i$ in effective fields ${\mathbf{h}}_i=-\partial E/\partial {\mathbf{m}}_i$ which in addition to containing external magnetic fields, describe contributions from interatomic exchange interactions, long-range dipolar interactions, anisotropy fields, etc. In this publication, we add the magnetic degrees of freedom to the widely used Gaussian approximation potential of machine learning and present a model that describes the potential energy surface of a crystal based on atomic coordinates and noncollinear magnetic moments. Incorporating the translational, rotational, inversion, and permutational symmetries of magnetic interactions, the ML model can describe various magnetic interactions expanded into two-body, three-body terms, etc., in the spirit of the atomic cluster expansion. Assuming an adiabatic approximation for the spin directions, the ML model depends solely on the positions and orientations of atomic spins and is computationally efficient enough to make coupled ab initio molecular and spin dynamics possible. To illustrate the ML model, we implement a two-body form for the interatomic exchange interaction. Comparing the total energies and local exchange fields predicted by the model for noncollinear spin arrangements with the results of constrained noncollinear density functional calculations for bcc Fe yields very good results, with agreement on the level of 1 meV/spin for the total energy.

Transport properties of single- and two-site mesoscopic quantum Hall (QH) circuits at high transparencies can be described in terms of the lowest-order backscattering processes, enabling a mapping to the boundary sine-Gordon model. We show that this description breaks down in circuits with four or more sites, where higher-order backscattering processes become relevant and qualitatively modify the low-energy physics, while remaining exactly marginal in three-site geometries. Focusing on the four-site circuit, we derive an effective low-energy theory that captures the resulting interaction-driven physics and reveals the emergence of unique quantum critical points. In the vicinity of these critical points, we obtain universal conductance and scaling behavior and establish the robustness of the associated non-Fermi liquid physics. We further introduce tunneling in multichannel multisite QH circuits and propose a promising route for realizing diverse quantum critical phenomena. We show that a boundary sine-Gordon description can be restored in multichannel multisite QH circuits by appropriately looping selected edge channels, a procedure that is experimentally feasible. Finally, we analyze the nonequilibrium heating effects relevant to transport measurements in QH circuits. Altogether, our results establish multisite QH circuits as a versatile and highly controllable platform for simulating interaction-driven quantum critical phenomena.

The two-dimensional (2D) materials with coexistence of Dirac points and Van Hove singularities (VHSs) provide a promising platform for seeking topological superconductivity or ferromagnetism at high critical temperatures. However, ideal examples combining electronic topological properties with superconductivity or ferromagnetism are scarce. Here, through structural search, we identify 2D ${\mathrm{Sc}\mathit{X}\mathrm{S}}_2$ ($X$ = Rh, Ta, Mo) monolayers with simple square or rectangular lattices, where VHSs lie near Dirac points close to the Fermi levels. Using first-principles calculations, Bardeen-Cooper-Schrieffer theory, and Monte Carlo simulations, we found that all the three monolayers exhibit nontrivial topological electronic properties. Moreover, ${\mathrm{ScRhS}}_2$ is intrinsically superconducting with Tc = 1.36 K; ${\mathrm{ScTaS}}_2$ shows tunable superconductivity reaching Tc = 2.21 K under 6% uniaxial tensile strain which also displays ferroelasticity induced by the Jahn-Teller effect; and ${\mathrm{ScMoS}}_2$ hosts a topological ferromagnetic half-metal ground state with a giant anomalous Hall effect and Curie temperature of 329 K stabilized by a high magnetic anisotropy energy of 1.837 meV/Mo. These results establish ${\mathrm{Sc}\mathit{X}\mathrm{S}}_2$ monolayers as a versatile 2D material family for exploring exotic mixtures of topological states, superconductivity, and half-metal ferromagnetism, offering potential for novel electronic and spintronic applications.

We develop a microscopic theory of the trion polaron: a bound state of two electrons and one hole, dressed by longitudinal optical (LO) phonons. Starting from the Fröhlich Hamiltonian, which describes the interaction of charged particles with LO phonons in three-dimensional (bulk) and two-dimensional (monolayer) polar crystals, we adopt the intermediate-coupling variational approximation of Lee, Low, and Pines, and generalize it for the three-body problem. This yields an effective three‐particle Hamiltonian with renormalized electron-electron and electron-hole interactions, similar to those obtained for exciton polaron and bipolaron problems. We compute the binding energies for a family of bulk perovskite materials and several atomic monolayer materials characterized by pronounced polar effects, providing quantitative benchmarks for spectroscopic measurements.

Topology and nonlinearity are deeply connected. However, whether topological effects can arise solely from the structure of nonlinear interaction terms, and the nature of the resulting topological phases, remain to large extent open questions. Here we consider a chain of parametrically driven quantum resonators coupled only via weak nearest-neighbor cross-Kerr interaction, without any quadratic tunneling term. We show that, when the drive overcomes a critical threshold value, the system undergoes a transition from the atomic limit of decoupled oscillators to a symmetry-broken topological phase. The topology is determined by the interplay of local and nearest-neighbor Kerr nonlinearities, yielding a nontrivial bulk-boundary correspondence. In the topological phase, we derive analytical approximations for the low-energy spectrum, identifying the conditions to observe topological edge modes.

Understanding thermal properties of materials is fundamental to technological applications and to discovering new phenomena. In particular, advances in experimental techniques such as cold-atom measurements allow the simulation of paradigmatic Hamiltonians with great control over model parameters, such as the Hubbard model. One aspect of this model which is not much explored is the behavior of the specific heat as a function of density. In this work, we perform determinant quantum Monte Carlo simulations of the Hubbard model interpolating between the square and triangular lattices to analyze the specific heat as the filling, interaction, and temperature of the system are changed. We found that, with strong correlations, the specific heat presents a three-maxima structure as a function of filling, with local minima between them. This effect can be explained by a decomposition of kinetic and potential contributions to the specific heat, demonstrating interesting phenomena away from the commonly studied half-filling regime. Moreover, by analyzing the kinetic contribution in momentum space we show that, connected to this specific heat behavior, there is a density anomaly detected through the thermal expansion coefficient. These momentum-space quantities are accessible using cold-atom experimental measurements at multiple temperatures. Finally, we map the location of these phenomena and connect the thermal expansion anomaly with the well-known Seebeck coefficient change of sign. Our results provide an alternative perspective to analyze this change of sign.

Kagome metals provide a material platform for probing new correlated quantum phenomena due to the naturally incorporated linear dispersions, flat bands, and Van Hove singularities in their electronic structures. Among these quantum phenomena is the charge density wave (CDW), or the distortion of the lattice structure due to the motion of correlated electrons through the material. CDWs lower the energy of the compound, creating an energy gap that facilitates behaviors akin to superconductivity, nonlinear transport, or other quantum correlated phenomena. The kagome metal FeGe has been shown to host a CDW transition at approximately 100 K, and its occurrence is strongly influenced by the sample annealing conditions. However, a notable gap in the literature is the lack of clear thermoelectric transport evidence for electronic structure changes associated with this CDW transition. Here, we present evidence of electron behavior modification due to annealing disorder via thermoelectric measurements on FeGe crystals presenting a CDW transition and those without a CDW. The observed Nernst effect and Seebeck effects demonstrate pronounced modifications of electrical transport properties associated with CDW formation and its suppression by annealing-induced disorder, including a change in the thermopower sign and a strong enhancement of the Nernst response in the CDW state. Our results provide evidence of multiple phase transitions, which confirms the influence of CDW on the thermal properties of FeGe and demonstrates the suppression of CDW with sufficient disordering.

We investigate the microwave absorption spectra of a split-ring resonator (SRR) based on a high-mobility two-dimensional electron system (2DES) in an AlGaAs/GaAs heterostructure. Introducing a split into the ring-shaped mesa gives rise to an additional plasmon resonance exhibiting strong polarization dependence. The frequency of the split-induced mode displays a negative magnetic-field dependence, while its dispersion is characteristic of one-dimensional plasma excitations. We also address the tunability of the plasmon resonances in the SRR-shaped 2DES.

Topological thermal transport offers a quantum route to regulate heat flow through Berry-curvature-driven responses. However, approaches for dynamically switchable control of such transport are lacking. Here, we propose an interlayer-sliding-driven dynamical evolution mechanism to control topological thermal transport in bilayer antiferromagnetic electron crystals, exemplified by ${\mathrm{ScI}}_2$. Sliding breaks spin group symmetry, generates ferroelectric polarization, and reshapes layer-resolved Berry curvature, resulting in strong modulation of anomalous Nernst and thermal Hall conductivities as signatures of topological phase transitions. Giant thermal Hall peaks and Hall plateaus emerge under sliding, demonstrating amplified topological heat transport response. Reversing the sliding direction switches spin splitting and transport polarity, enabling direct reading of stacking order and motion direction. Our work uncovers topological thermoelectric characteristics and superior transport performance in sliding systems, providing new insights for thermoelectric device design and applications.

We report a gate-tunable magnetoresistance and nonlinear Hall effect in thin ${\mathrm{Bi}}_y{\mathrm{Sb}}_{2-y}{\mathrm{Te}}_{3-x}{\mathrm{Se}}_x$ films grown by molecular beam epitaxy. The Hall coefficient $R_H$ exhibits distinct nonlinear behavior controlled by the gate voltage: a $\sim 2\%-3\%$ increase at low field ($B\sim 0.5\mathrm{T}$), opposite slopes for positive and negative gate biases at higher fields, and a substantial change at large negative gate voltages ($\sim -90\mathrm{V}$). Joint analysis of the gate dependences of magnetoresistance and the nonlinear Hall effect demonstrates a combined effect of topological surface states, trivial bulk states, holes in the inversion layer, and the smooth energy disorder, when the Fermi level is near the Dirac point. Because of the existence of several carrier groups, quantum corrections to the conductivity manifest themselves not only in the magnetoresistance, but also in the Hall effect. Our model quantitatively reproduces the gate dependence of both longitudinal and Hall resistances, allowing us to determine the concentrations and mobilities of all contributing carrier types.

Cavity optomechanical systems enable coherent photon-phonon interactions essential for quantum technologies, yet high-performance devices have been limited to suspended structures. Here, we overcome this limitation by demonstrating cavity Brillouin optomechanics in a suspension-free racetrack microring resonator on a lithium-niobate-on-sapphire chip, a platform that merits high stability and scalability. We demonstrate coherent coupling between telecom-band optical modes and a 9.6 GHz phonon mode, achieving a maximum cooperativity of 0.41 and a phonon quality-factor-frequency product of ${10}^{13}\mathrm{Hz}$. The momentum-matching condition inherent to traveling-wave Brillouin interactions establishes a one-to-one mapping between the optical wavelength and phonon frequency, enabling multichannel parallel operations across nearly $300\mathrm{MHz}$ in phonon frequency and $40\mathrm{nm}$ in optical wavelength. Our suspension-free architecture provides a coherent photon-phonon interface compatible with wafer-scale integration, opening pathways toward hybrid quantum circuits that unite photonic, phononic, and superconducting components on a single chip.

The Wang-Teter (WT)-like nonlocal kinetic energy density functional (KEDF) in the framework of orbital-free density functional theory, while successful in some bulk systems, exhibits a critical Blanc-Cancès instability [J. Chem. Phys. 122, 214106 (2005)] when applied to isolated systems, where the total energy becomes unbounded from below. We trace this instability to the use of an ill-defined average charge density, which causes the functional to simultaneously violate the scaling law and the positivity of the Pauli energy. By rigorously constructing a density-functional-dependent kernel, we resolve these pathologies while preserving the formal exactness of the original framework. By systematically benchmarking single-atom systems of 56 elements, we find the resulting KEDF retains computational efficiency while achieving an order-of-magnitude accuracy enhancement over the WT KEDF. In addition, this proposed KEDF preserves WT's superior accuracy in bulk metals, outperforming the semilocal functionals in both regimes.

Topological point states (TPSs) have the same physical mechanism as that of the topological corner states (TCSs) in higher-order topological insulators (HOTIs) in two-dimensional (2D) systems and bring a new physical perspective and application prospect to HOTI. However, the current research on TPSs is limited to periodic structures and Hermitian systems. The special structure of quasicrystals and the skin effect in non-Hermitian systems may bring new physical phenomena to TPSs. In this paper, the TPSs are discovered in non-Hermitian quasicrystals, and the consistency between the two point vacancies for TPSs and the two ends of a 1D topological chain is demonstrated. TPSs will provide a method for the localization control of non-Hermitian quasicrystals.

The coupling between ferroelectricity and ferromagnetism in two-dimensional (2D) materials provides a promising pathway for the realization of electric-field-controlled spintronic devices. In this work, we unveil the microscopic mechanism underlying polarization-dependent magnetic anisotropy in the ferroelectric monolayer ${\mathrm{InCrTe}}_3$ through first-principles calculations. The monolayer ${\mathrm{InCrTe}}_3$, composed of five atomic sublayers with a ${\mathrm{Te}}_{\mathrm{I}}$-Cr-${\mathrm{Te}}_{\mathrm{II}}$-In-${\mathrm{Te}}_{\mathrm{III}}$ stacking sequence, exhibits two inequivalent polar states: a metallic $\mathrm{P}\uparrow$ state with tetrahedral Cr-Te coordination and an insulating $\mathrm{P}\downarrow$ state with octahedral coordination. We show that a substantially larger out-of-plane magnetic anisotropy energy (MAE) in the $\mathrm{P}\uparrow$ state arises from structural transformation and electronic reconstruction associated with a polar structural transition. In the metallic $\mathrm{P}\uparrow$ state, the central ${\mathrm{Te}}_{\mathrm{II}}$ atom undergoes a pronounced out-of-plane distortion, driving its $p$ orbitals closer to the Fermi level. The resulting hybridization between ${\mathrm{Te}}_{\mathrm{II}}\text{−}p$ and Cr-$d$ states enhances spin-orbit coupling (SOC), positioning ${\mathrm{Te}}_{\mathrm{II}}$ as a key SOC hotspot responsible for the large out-of-plane MAE. In contrast, in the insulating $\mathrm{P}\downarrow$ state, the more symmetric octahedral crystal field shifts the Te-$p$ states to lower energies, suppressing orbital mixing and reducing the out-of-plane MAE. These findings provide insight into how polar structural changes can modulate SOC-driven magnetic anisotropy through orbital engineering, offering a microscopic design principle for electrically controllable 2D multiferroic and spintronic devices.

The moderate synthesis conditions of $\mathrm{Ce}{\mathrm{H}}_9$ under cold compression demonstrate its remarkable chemical precompression effect, while the single occupied $4f$ electron configuration of Ce contributes to the rich chemical and physical properties observed in cerium-bearing compounds. In collaboration with machine-learning-accelerated crystal structure prediction, we predicted a thermodynamically stable superconducting phase $\mathrm{CeS}{\mathrm{c}}_2{\mathrm{H}}_{24}$ at 200 GPa. With considering more accurate quantum anharmonic effects, the thermodynamically stable pressure of $\mathrm{CeS}{\mathrm{c}}_2{\mathrm{H}}_{24}$ is further decreased to 117 GPa, at which pressure it exhibits a high superconducting critical temperature ($T_{\mathrm{c}}$) of ∼210 K. We found a different framework of bonding theory for hydrogen-based superconductors where strong metallic bonds in hydrides originate from near-free electronic states between the highest effective energy level and the Fermi level. Specifically, the delocalization of Ce-$4f$ orbitals in $\mathrm{CeS}{\mathrm{c}}_2{\mathrm{H}}_{24}$ provided a number of near-free electrons, thereby greatly enhancing metallic bonds and making the system energetically much more favorable. Our theory for $\mathrm{CeS}{\mathrm{c}}_2{\mathrm{H}}_{24}$ emphasizes the non-negligible role of metallic bonding in hydrides, which paves the way for developing high-temperature superconductors under experimentally accessible pressures.

Quantum fluctuations in low-spin $(S=\frac{1}{2})$ systems make them potential materials to investigate various intriguing field-induced quantum phenomena. In this context, rare-earth $\left(4f\right)$-based effective spin $(J_{\mathrm{eff}}=\frac{1}{2})$ systems with localized magnetic moments and low energy scales offer an advantage of low critical fields and provide access to probe the complete magnetic phase diagram. Here, we present inelastic neutron scattering (INS) data to understand the crystal field (CF) scheme of the previously established $J_{\mathrm{eff}}=\frac{1}{2}$ antiferromagnet ${\mathrm{NdVO}}_4$, along with low-temperature magnetization and heat capacity measurements to construct the complete magnetic phase diagram. Our INS data validate the presence of the $J_{\mathrm{eff}}=\frac{1}{2}$ state at low temperatures with the ground and first excited CF state separated by an energy of 140 K. Furthermore, it yields a unique CF scheme where the excitation corresponding to the highest (fourth) CF state is observed via transitions involving the first and second excited states. Magnetic and heat capacity measurements yield the presence of a field-induced first-order spin-flop transition within the second-order antiferromagnetic (AFM) state. Magnetic phase diagrams constructed using the field-dependent magnetization and magnetic heat capacity reveal a continuous transformation from AFM to spin-flop state with a critical field of $H_{\mathrm{sf}}\sim 1.4\mathrm{T}$. The presence of quantum fluctuations near $H_{\mathrm{sf}}$ are evident from the V-shaped region in entropy contours indicating the presence of accumulated entropy.