We examine the dynamics, Hall angle, and pinning for Néel skyrmions in an altermagnet. Using an atomistic model, we show that skyrmion velocity and Hall angle dependence are anisotropic with respect to the direction of the drive, due to the fourfold symmetry implied by the two sublattices of the altermagnet. The skyrmion Hall angle and velocity at fixed drive show strong variations for increasing ratios of the exchange constant of the sublattices, $J_2/J_1$. This fourfold anisotropy of altermagnetic (ATM) skyrmions also leads to anisotropic pinning effects for an ATM skyrmion interacting with isotropic circular pinning sites. We also propose a simple particle model for this system that takes into account this anisotropy and find that it captures both the variations of the ATM skyrmion Hall angle and velocity as a function of drive direction, as also found in the atomistic simulations. Using this particle model, we examine ATM skyrmions interacting with a periodic array of pinning sites. For increasing ratios of $J_2/J_1$, we find a strongly nonmonotonic ATM skyrmion velocity, where there is a minimum in the velocity where the skyrmion locks to different symmetry directions of the periodic pinning lattice. For a random array, we find that ATM skyrmions show strongly anisotropic depinning thresholds and velocity responses for different drive directions, and that the Hall angle is nearly constant with drive. In comparison, for the same parameters, the depinning threshold for a ferromagnetic (FM) skyrmion is lower, and the skyrmion Hall angle shows a strong velocity dependence. The lower depinning threshold for FM skyrmions is due to stronger Magnus forces.

The interplay among superconductivity, magnetism, and nontrivial band topology represents one of the most compelling frontiers in condensed matter physics. The exploration of novel superconductivity in $3d$ transition-metal compounds, particularly the rare Cr-based systems containing strongly magnetic Cr ions, has long attracted attention owing to their unconventional pairing mechanisms that challenge conventional wisdom. Yet, Cr-based superconductors remain scarce, especially those possessing nontrivial topological character, underscoring the urgent need to uncover new members. Here we report the observation of superconductivity in the pressure-amorphized Cr-based topological insulator $\mathrm{Cr}{\mathrm{P}}_4$. Upon compression, $\mathrm{Cr}{\mathrm{P}}_4$ undergoes an anomalous quantum phase transition from a metallic to a semiconductinglike state at around 15 GPa, driven by significant changes in the electronic structure. At approximately 70 GPa, re-metallization with superconductivity occurs alongside an irreversible amorphization. The superconducting transition temperature $T_{\mathrm{c}}$ increases monotonically with pressure, reaching 4.8 K at 141.3 GPa. Furthermore, theoretical calculations predict multiple topological phase transitions from a strong topological insulator to a trivial state and finally back to a strong topological state under pressure. Our study not only establishes $\mathrm{Cr}{\mathrm{P}}_4$ as the first Cr-based amorphous superconductor but also opens a new paradigm for exploring superconducting and topological properties in amorphous materials.

The expectation value of the twist operator has been widely used as a polarization-based index for gapped and gapless phases in interacting quantum many-body systems. Although numerous studies support this usage in specific settings, and rigorous results have established the validity of the criterion in important settings, the precise assumptions required for it to sharply distinguish gapped and gapless phases under more general conditions have not been fully clarified. In this work, we clarify the logical status of polarization-based indices by formulating symmetry-based statements under explicitly stated assumptions. We identify the role of ground-state degeneracy in the statements for gapped systems and clarify the distinct assumptions required to exclude gapless scenarios that could otherwise mimic gapped behavior in the thermodynamic limit. Building on this controlled framework, we construct a meaningful extension beyond one dimension, emphasizing that such an extension is nontrivial and cannot be obtained by a straightforward generalization of the one-dimensional twist operator. Our results delineate the regime in which polarization-based quantities are justified as sharply defined many-body indices.

Two-dimensional hole gases (2DHGs) confined in Ge/SiGe quantum wells offer a promising platform for exploring low-dimensional spintronic phenomena and valence band dynamics, due to their strong spin-orbit interaction and long spin coherence times. Biaxial compressive strain arising from the lattice mismatch between the Ge well and SiGe barriers defines the fundamental physical properties of the 2DHG. Meanwhile, practical device architectures introduce additional sources of strain. For instance, differential thermal contraction between gate electrodes and the quantum well leads to anisotropic strain, which in turn modulates the electronic structure and transport symmetry. This paper provides a systematic and quantitative investigation into the impact of deliberately in situ applied uniaxial strain on the properties of the 2DHG in Ge/SiGe quantum wells. Using a piezoelectric-based strain cell, uniaxial in-plane strain along the $\left[110\right]$ crystallographic direction is applied and magnetotransport measurements are performed. The results reveal significant anisotropic modulation of the hole effective mass, mobility, and out-of-plane $g$-factor due to strain-induced deformation of the valence band. While the carrier density remains isotropic, the modification of mobility, effective mass, and the out-of-plane $g$-factor show pronounced anisotropy along different crystallographic directions. These findings highlight the critical role of uniaxial strain in shaping the fundamental transport coefficients of Ge/SiGe quantum wells and provide precise experimental benchmarks for strain engineering in future design of high-performance heterostructures and devices.

Chiral molecules are known to preferentially select electrons with a particular spin state, an effect termed chirality-induced spin selectivity (CISS). In this work, the transient CISS dynamics in a chiral molecule are investigated through time-dependent quantum-transport simulations, an important step toward further understanding CISS and its application in devices such as magnetoresistive random access memories and spin-based quantum computers. We show that the spin-dependent group velocity of electrons is a possible contributor to a nonzero occupancy-based spin polarization throughout the chiral molecule. Contrary to the case in which a chiral molecule is connected to a single lead, this spin polarization persists into the steady state when two leads are connected. We show that the simulated spin polarization qualitatively agrees with a reference experiment, as evidenced by the distinct magnetic-field signatures calculated from the spin polarization within a monolayer of chiral molecules.

Hexagonal boron nitride (hBN) flakes are key building blocks for encapsulating two-dimensional (2D) materials, providing atomically flat surfaces and an excellent dielectric environment for high-mobility field-effect transistors and tunneling devices. However, strain induced during mechanical exfoliation and assembly of van der Waals heterostructures may lead to plastic deformations of the hBN surface, injecting dislocation lines between the topmost layer and the underlying film. Since a monolayer of hBN is noncentrosymmetric and exhibits a piezoelectric response to deformation, individual dislocations and, in particular their networks, can generate electrostatic-potential modulations in the encapsulated 2D material. Here, we examine scenarios in which the top hBN layer is uniaxially strained and/or twisted, and show how lattice reconstruction into dislocation networks leads to the formation of piezoelectric-charge hotspots that effectively behave as charged defects.

Two-dimensional Fermi liquids at low temperatures have been theoretically established to exhibit an odd-even effect in the collective quasiparticle relaxation rates where even-parity deformations of the Fermi surface decay at a much faster rate than odd-parity ones. A predicted consequence of this effect is a new tomographic transport regime that mixes hydrodynamic and collisionless transport. In the presence of a magnetic field, however, the tomographic regime is expected to evolve towards conventional transport regimes as soon as the cyclotron radius becomes smaller than the dominant odd-parity mean-free path. In this work, we examine this transition from the point of view of collective modes, using a numerically exact solution of the linearized Boltzmann equation within a generalized relaxation time approximation for the odd-parity and even-parity modes. In the absence of a magnetic field, the transverse conductivity exhibits two diffusive tomographic collective modes, and we find that at a critical magnetic field one of these two tomographic modes disappears. Which tomographic mode persists depends on the Landau parameters, and becomes increasingly dominated by hydrodynamic modes at high fields. We corroborate our analysis using a variational approach for the Fermi surface deformation that captures the angular structure of the deformation and the critical magnetic field strength. The collective modes discussed here can in principle be observed by examining the damping of longitudinal and transverse current responses in finite magnetic fields.

Lithium carbide (${\mathrm{Li}}_2{\mathrm{C}}_2$), a potential electrode material for lithium ion batteries, has recently gained attention as a promising tritium breeding material for magnetic confinement fusion reactor owing to its higher breeding ratio compared to conventional ternary ceramics. Motivated by the reported pressure-induced $Immm\to Pnma$ structural phase transition in ${\mathrm{Li}}_2{\mathrm{C}}_2$ [I. Efthimiopoulos et al., Phys. Rev. B 92, 064111 (2015)], previously we had investigated pressure dependence of structural, dynamical, electronic, and mechanical properties of these two phases. However, for prospective applications in fusion reactors and energy-storage technologies, a comprehensive understanding of its thermal response under extreme thermodynamic conditions is essential. In this work, we present a comprehensive ab initio investigation of the thermophysical behavior of the aforementioned phases over a wide range of temperatures (0–900 K) and hydrostatic pressures (0–25 GPa). Various thermodynamic quantities including thermal expansion coefficient, isothermal and adiabatic bulk moduli, isochoric and isobaric heat capacities, Debye temperature, and ion thermal conductivity are systematically evaluated. The findings highlight significant changes in the thermal response among two allotropes of ${\mathrm{Li}}_2{\mathrm{C}}_2$. A unique class of exponential functions is proposed to describe the temperature dependence of thermophysical parameters for both phases of ${\mathrm{Li}}_2{\mathrm{C}}_2$. Additionally, the pressure dependence of all studied thermophysical parameters is found to conform to a generalized power-law relationship. Study enabled estimating shock Hugoniot parameters, a prerequisite for understanding dynamic response of a material. The volume dependence of Grüneisen parameter is determined and compared with analytical models proposed by Slater, Dugdale and MacDonald, Vaschenko and Zubarev, and scaling law of Meyers. Study reveals that the Vaschenko-Zubarev model and scaling law follow closely with ab initio results, whereas others deviate significantly. The compression-dependent Grüneisen parameter is then utilized to predict melting curve of this compound. Finally, study is extended to construct high-temperature high-pressure equation of state of ${\mathrm{Li}}_2{\mathrm{C}}_2$. This comprehensive analysis provides valuable insights into the behavior of ${\mathrm{Li}}_2{\mathrm{C}}_2$ under different thermodynamic conditions, and supports its potential application as a tritium breeding material in fusion energy systems.

Current-induced spin-orbit torque has emerged as a powerful technique for manipulating magnetization switching of ferromagnet/nonmagnet (FM/NM) based memory cell. By investigating nonequilibrium spin torque effect in a van der Waals heterobilayer, trigonal ${\mathrm{Cr}}_3{\mathrm{Te}}_4/{\mathrm{PtTe}}_2$, the first-principles quantum transport calculations are applied to determine both local spin induction, resulting from Rashba-Edelstein effect in the FM layer, and spin current injection, flowing from the NM to the FM layer. Our work reveals that local spin induction significantly generates the fieldlike torque, which primarily governs the switching current in systems with strong in-plane magnetic anisotropy. Our work emphasizes the importance of optimizing spin Hall effect in the NM layer for perpendicular magnetic anisotropy (PMA)-based magnetization switching and maximizing the Rashba effect in the FM layer for in-plane magnetic anisotropy (IMA)-based switching.

We report a dynamic magnetostrictive effect in type-II superconductors (e.g., Nb, ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7\text{−}x}$, ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$ and ${\mathrm{Ba}}_{0.6}{\mathrm{K}}_{0.4}{\mathrm{Fe}}_2{\mathrm{As}}_2$) and any type-II superconductor is expected to present a similar response to this new technique. Measured via a composite magnetoelectric technique, an ac field excites an in-phase, nondissipative strain response scaling linearly with vortex density in the vortex lattice phase. In the vortex liquid phase, the signal acquires an out-of-phase component before vanishing in the normal state. We propose the ac strain susceptibility a thermodynamic criterion for the vortex lattice, capturing vortex collective modes inaccessible from static measurements.

The Remeika stannides ($R_3{\mathrm{T}}_4{\mathrm{Sn}}_{13}$, with R = rare earth/alkaline metals, T = transition metal, and X = p-block elements) have been extensively studied due to the interplay between the charge-density-wave (CDW) ordering and superconductivity often found in these materials. Here, we explore the relationship between these two orders in cubic ${\mathrm{La}}_3{\mathrm{Co}}_4{\mathrm{Sn}}_{13}$ by conducting electrical transport measurements under uniaxial stress along different crystallographic directions ([100], [110], and [111]). We find that the superconducting transition temperature $\left(T_{\mathrm{c}}\right)$ is suppressed under compression for all directions measured, in contrast to previous measurements under hydrostatic pressure. This indicates $s$-wave superconductivity. The CDW transition temperature is also suppressed under compression for all measured directions. The simultaneous suppression of superconductivity and CDW order suggests that changes in $T_{\mathrm{c}}$ with uniaxial stress are mainly driven by changes in the electronic density of states and not a competition between these two orders.

We investigated the effects of Ni doping on carrier density and anomalous electrical transport properties in ${\mathrm{CeCo}}_{1-x}{\mathrm{Ni}}_x{\mathrm{In}}_5$ $(x\le 0.3)$ by performing Hall resistivity measurements. The carrier density, estimated from the Hall coefficient $R_{\mathrm{H}}$ at a temperature of 0.5 K in high magnetic fields, increases linearly with $x$, indicating that the doped Ni ions act as electron dopants. In ${\mathrm{CeCoIn}}_5$, the magnitude of $-R_{\mathrm{H}}$ is strongly enhanced at magnetic fields near the superconducting upper critical field $H_{c2}$ and in the low-field region above the superconducting transition temperature $T_c$. However, these anomalies are found to be significantly suppressed by Ni doping. Possible origins of this suppression in $-R_{\mathrm{H}}$ are discussed.

As a powerful theoretical construct, the entanglement Hamiltonian (EH) encapsulates the essential entanglement properties of a quantum many-body system. From the EH, one can extract a variety of entanglement quantities, such as entanglement entropies, negativity, and the entanglement spectrum. However, its general analytical form remains largely unknown. While the Bisognano-Wichmann theorem gives an exact EH form for Lorentz-invariant field theories, its validity on lattice systems is limited, especially when Lorentz invariance is absent. In this work, we propose a general scheme based on the lattice-Bisognano-Wichmann (LBW) ansatz and multi-replica-trick quantum Monte Carlo methods to numerically reconstruct the entanglement Hamiltonian in two-dimensional systems and systematically explore its applicability to systems without translational invariance, going beyond the scope of the original Bisognano-Wichmann theorem. Various quantum phases—including gapped and gapless phases, critical points, and phases with either discrete or continuous symmetry breaking—are investigated, demonstrating the versatility of our method in reconstructing entanglement Hamiltonians. Furthermore, we find that when the entanglement boundary of a system is ordinary (i.e., free from surface anomalies), the LBW ansatz provides an accurate approximation well beyond Lorentz-invariant cases. Our work thus establishes a general framework for investigating the analytical structure of entanglement in the complex quantum many-body systems.

The quantum metric, the real part of a quantum geometric tensor, plays an important role in fundamental transport and optical responses of quantum materials. While net quantum metric effects are typically realized by breaking both time-reversal ($\mathcal{T}$) and inversion ($\mathcal{P}$) symmetries, valley-contrast mechanisms enable the probing of quantum geometry in centrosymmetric, nonmagnetic systems, revealing physical signatures beyond Berry curvature. Here, we design a four-layer ${\mathrm{MoS}}_2$ platform that combines sliding antiferroelectric order with strain-induced $C_{3z}$ breaking to realize a quantum metric driven nonlinear valley Hall effect (NVHE) under preserved $\mathcal{P}$ and $\mathcal{T}$ symmetries. Reversible interlayer sliding ($\mathrm{ABBA}\leftrightarrow \mathrm{BAAB}$) provides nonvolatile electrical control of the valley response. First-principles calculations reveal an outer-layer-dominated NVHE with tunable sign and magnitude. This symmetry-preserving, sliding-tunable strategy activates hidden quantum geometric phenomena in realistic two-dimensional materials and opens a clean pathway for tunable valleytronics and quantum information devices.

The Berry curvature, akin to the magnetic field in reciprocal space, provides an intriguing avenue for exploring unique electromagnetic phenomena devoid of real-space analogs. In this work we investigate reciprocal-space electromagnetic induction, including the contributions from time-varying Berry curvature and the magnetic charge current in topological semimetals, where a nodal line and Weyl nodes coexist under a driving term. We find that the Berry curvature along the nodal loop is nonuniform: it aligns with the azimuthal direction on one half of the loop, while on the other half, it points antiparallel. Moreover, as the Weyl node moves in reciprocal space, its monopole charge can change sign. As a result, the average emergent electric field passing through the nodal loop or the Weyl point's motion orbit does not consistently align with its normal direction. Instead, one half of the field is parallel to the normal, while the other half is antiparallel. In both cases the total emergent electric field in reciprocal space sums to zero. However, by connecting the topological semimetal to an electrode, we can detect the electric field with a nonzero local average through the quantum pumping effect. Our research sheds light on different types of electromagnetic induction effect, thus broadening our comprehension of electromagnetic phenomena.

Self-interaction error (SIE) is a well-known limitation of standard density functional theory (DFT), yet its significance for single-atom catalysts (SACs) remains largely overlooked. Here we show that correcting SIE via $\mathrm{DFT}+U$ is not merely a methodological refinement but a prerequisite for reliably predicting the electronic structure and catalytic activity of $3d$ metal-${\mathrm{N}}_4$ SACs, especially for near-half-filled $d$-shell systems (Mn, Fe, Co, Ni). These SACs exhibit pronounced $U$-sensitivity, manifesting as $d$-level shifting and spin-state transitions driven by the interplay between on-site Coulomb repulsion and the quasi-$D_{4h}$ ligand field. Crucially, this sensitivity translates directly to catalysis. Using the oxygen reduction reaction as a model reaction, we find that $\mathrm{DFT}+U$, in agreement with experiments, successfully predicts $\mathrm{Fe}\text{−}{\mathrm{N}}_4$ to be the more active catalyst than $\mathrm{Co}\text{−}{\mathrm{N}}_4$, whereas standard DFT fails. This reversal originates from a downshift of occupied $d$ orbitals that weakens hybridization with ${}^{*}\mathrm{OOH}$ and ${}^{*}\mathrm{OH}$. Interestingly, for ${\mathrm{Fe}}^{*}\mathrm{O}, {\mathrm{Co}}^{*}\mathrm{O}$, and ${\mathrm{Mn}}^{*}\mathrm{OH}$, a spin-state transition partially offsets this weakening via Hund's exchange, leading to a less pronounced decrease in adsorption energy. These findings establish that SIE correction is essential for reliable SAC modeling, particularly for near-half-filled $d$-shell systems, and our work provides a mechanistic framework to understand its impact on catalytic predictions.

While charge density waves (CDWs) are a hallmark of the kagome metal $\mathrm{Cs}{\mathrm{V}}_3{\mathrm{Sb}}_5$, their absence in the bilayer counterpart $\mathrm{Cs}{\mathrm{V}}_6{\mathrm{Sb}}_6$ remains a notable exception, with the underlying mechanism yet to be elucidated. Here, integrating ultrafast spectroscopy with first-principles calculations, we demonstrate that the lack of charge orderings in $\mathrm{Cs}{\mathrm{V}}_6{\mathrm{Sb}}_6$ originates from a synergy between an altered electronic structure and fundamentally weakened electron-lattice coupling. Experimentally, coherent phonon dynamics exhibit purely conventional anharmonic behavior without CDW-associated anomalies, while electron dynamics reveal a markedly reduced electron-phonon coupling strength (i.e., 0.13 in $\mathrm{Cs}{\mathrm{V}}_6{\mathrm{Sb}}_6$ versus 0.88 in $\mathrm{Cs}{\mathrm{V}}_3{\mathrm{Sb}}_5$). Consistent with these experimental observations, first-principles calculations indicate an absence of Fermi-surface nesting and a shift of Van Hove singularities away from the Fermi level in $\mathrm{Cs}{\mathrm{V}}_6{\mathrm{Sb}}_6$. Together, our results establish a unified physical picture in which suppressed electronic instabilities and weak lattice coupling preclude CDW formation in bilayer kagome metals.

Motivated by recent developments in the study of quasi-one-dimensional iron systems with ${\mathrm{Fe}}^{2+}$, we comprehensively study an ${\mathrm{Fe}}^{3+}$ chalcogenide chain system. Based on first-principles calculations, the ${\mathrm{Fe}}^{3+}$ chain has a similar electronic structure to that discussed before for the ${\mathrm{Fe}}^{2+}$ chain, because of the similar $\mathrm{Fe}{X}_4$ ($X=\mathrm{S}$ or Se) tetrahedron-chain geometry. Furthermore, a three-orbital electronic Hubbard model for this chain was constructed using the density matrix renormalization group method. A robust antiferromagnetic coupling was unveiled in the chain direction. In addition, in the intermediate electronic correlation $U/W$ region, we found an interesting orbital-selective Mott phase with the coexistence of localized and itinerant electrons ($U$ is the on-site Hubbard repulsion, while $W$ is the electronic bandwidth) based on the orbital-selective behavior observed in the charge fluctuations. Furthermore, we do not observe any obvious pairing tendency in the ${\mathrm{Fe}}^{3+}$ chain in the electronic-correlation $U/W$ region, where superconducting pairing tendencies were reported before in iron ladders. This suggests that superconductivity is unlikely to emerge in the ${\mathrm{Fe}}^{3+}$ systems. Our results clearly establish the similarities and differences between ${\mathrm{Fe}}^{2+}$and ${\mathrm{Fe}}^{3+}$ iron chains, as well as iron ladders.