We present thermodynamic and spectroscopic measurements for an orthopyroxene ${\mathrm{CoGeO}}_3$ with magnetic ${\mathrm{Co}}^{2+}$ ions that form quasi-one-dimensional ladders. We show that noncollinear magnetic order below $T_N=32$ K can be stabilized by a strong local easy-axis anisotropy of $j_{\text{eff}}=1/2$ moments, which is induced by ligand octahedra distortions. Extraction of a magnetic Hamiltonian from inelastic neutron scattering measurements supports this interpretation and allows us to establish an effective magnetic model. The resulting exchange Hamiltonian justifies ${\mathrm{CoGeO}}_3$ as a realization of an Ising spin ladder compound.

Hydrogen, oxygen, and carbon are—based on solar system abundances—the main components of ice giants such as Uranus and Neptune, forming the C−H−O ternary mixture. In the planetary interiors, these materials are subjected to extreme temperature and pressure conditions exceeding 1000 K and 100 GPa. The three elements are assumed to mix in the icy mantles of Uranus and Neptune. However, only the pure C−H and ${\mathrm{H}}_2\mathrm{O}$ systems have been theoretically and experimentally investigated so far. Here, we identified candidate phase behaviors when the hydrogen, carbon, and oxygen completely mix in extreme conditions relevant to the ice giants by using ab initio molecular dynamics simulations. We reveal that the ternary system undergoes two types of superionicity at similar thermodynamic conditions to the middle icy mantles of Uranus and Neptune. In the first of these superionic phases, the hydrogen atoms diffuse within a fixed sublattice composed of carbon and oxygen. In the second phase, the hydrogen and carbon diffuse simultaneously throughout a fixed oxygen sublattice. Surprisingly, the hydrogen's diffusivity in the superionic phases of the ternary system exhibits an anisotropy, which cannot be seen in the pure superionic water. We further demonstrate the mechanisms of anisotropic hydrogen diffusivity from a microscopic perspective, combining Mulliken population analysis and the Nudged Elastic Band method. These findings provide a material basis for understanding the interior structures, thermal profiles, and enigmatic magnetic fields of the ice giants.

Here, we explore the role of inherent altermagnetic topology in transverse transport phenomena (such as crystal or anomalous Hall, Nernst, and thermal Hall effects) in several famous altermagnets, including tetragonal $X{\mathrm{V}}_{2}Y{}_2\mathrm{O}$ ($X=\mathrm{K},\mathrm{Rb},\mathrm{Cs}$; $Y=\mathrm{S},\mathrm{Se},\mathrm{Te}$), ${\mathrm{RuO}}_2, {\mathrm{MnF}}_2$, as well as hexagonal CrSb and MnTe. Notably, in $X{\mathrm{V}}_{2}Y{}_2\mathrm{O}$, the first experimentally realized layered altermagnets, transverse transport is governed by altermagnetic pseudonodal surfaces, emphasizing the purely topological contributions to transverse transport. Interestingly, we demonstrate that strain engineering and magnetic field, two unique methods for selectively controlling crystal and anomalous transport, can substantially enhance the magnitude of these phenomena while preserving the alternating spin characteristics in both real and momentum space. Moreover, due to the spin symmetry breaking via shear strain, a new magnetic phase, fully compensated ferrimagnetism, with isotropic spin splitting, can be induced. Our findings provide effective strategies not only for manipulating transverse transport in altermagnets but also for controlling magnetic phase transitions, offering valuable insights for their potential applications in spintronics and spin caloritronics.

The interplay between coupled degrees of freedom drives emergent phenomena such as ferroelectricity, multiferroicity, superconductivity, colossal magnetoresistance, and charge density waves. Advances in optical techniques now enable selective excitation of phonon modes, offering a pathway to manipulate other degrees of freedom, including orbitals and spin waves. However, a detailed understanding of how orbital and exchange interactions $J$ evolve under phonon excitation, and how this evolution modifies the spin wave, remains lacking. To address this gap, we investigate phonon-driven effects in the prototypical antiferromagnetic (AFM) oxide ${\mathrm{YCrO}}_3$, which exhibits contributions from all five partially occupied Cr $d$ orbitals. In the unperturbed ${\mathrm{YCrO}}_3$, the partially occupied orbitals, mediated by the ligand, have different overlap orientations, which induce competition between orbitals contributing to ferromagnetic (FM) and AFM interactions. Selective narrow- and finite-bandwidth phonon excitation perturbs the orbital overlaps and their relative contribution to FM and AFM interactions, lifts the degeneracies, renormalizes $J$'s, and significantly alters the spin waves. The renormalized $J$'s further modify the interatomic force constant and the phonons via a coupled spin-phonon Hamiltonian. Our quantitative analysis offers a deeper understanding of exchange pathways and spin dynamics under phonon excitations, opening opportunities for tailored magnetic functionalities in spintronics and quantum materials.

We present a comprehensive analysis of the critical behavior of ${\mathrm{Sm}}_7{\mathrm{Pd}}_3$ in the vicinity of its second-order magnetoelastic transition at $T_{\mathrm{c}}=173\mathrm{K}$. The critical exponents (CEs) $\beta$ and $\gamma$, determined using both the standard convergence procedure and the average normalized slope (ANS) method, diverge at $T_{\mathrm{c}}$–-a characteristic typically associated with first-order transitions. Notably, none of the established universality classes satisfactorily describe the critical behavior of ${\mathrm{Sm}}_7{\mathrm{Pd}}_3$, and we discuss the possible origins of this deviation in the context of the strong spin-lattice coupling intrinsic to the sample. We emphasize the importance of accurately selecting the critical temperature and magnetic field ranges to ensure robust critical behavior analysis, and propose a quantitative approach to assess the reliability of the extracted CEs. Additionally, we demonstrate that in the ANS method, the critical exponents $\beta$ and $\gamma$ should be calculated separately using data for $T⩽T_{\mathrm{c}}$ and $T⩾T_{\mathrm{c}}$, respectively. Our findings underscore the need for a revised theoretical framework to accurately describe second-order magnetoelastic transitions.

Thermal and electrical injection and transport of magnon spins in magnetic insulators is conventionally understood by the nonequilibrium population of magnons. However, this view is challenged by several recent experiments in noncollinear antiferromagnets, which urge a thorough theoretical investigation at the fundamental level. We find that the magnon spin in noncollinear magnets is described by a matrix, so even when the diagonal terms—spins carried by population—vanish, the off-diagonal correlations transmit magnon spins. Our quantum theory shows that a net spin flip of electrons in adjacent conductors creates quantum coherence between magnon states, which transports magnon spins in canted antiferromagnets, even without a definite phase difference between magnon modes in the incoherent process. It reveals that the pumped magnon correlation is not conserved due to an intrinsic spin torque, which causes dephasing and strong spatial spin oscillations during transport; both are enhanced by magnetic fields. Spin transfer to proximity conductors can cause extrinsic dephasing, which suppresses spin oscillations and thereby gates spin transport.

The theory of layered superconductors is extended in the presence of Rashba and Dresselhaus spin-orbit interactions (SOIs). Using the intralayer BCS-like pairing interaction and employing the Gor'kov formalism, we obtain analytical expressions for the temperature Green's functions and determine the gap function $\mathrm{\Delta }$ which becomes complex in the presence of SOIs. In the absence of SOIs, $\mathrm{\Delta }$ is isotropic at both zero and finite temperatures, but it becomes anisotropic even in the presence of a single SOI. This anisotropy is related to the extra $cos{k}_z$ factors in which the $k_z$ momentum along the $z$ direction contributes to the magnitude of the gap function. It is also found that SOIs suppress $\mathrm{\Delta }$ at both zero and finite temperatures, and for certain critical values of SOIs and beyond $\mathrm{\Delta }$ vanishes. Analytical expressions for the critical values of SOIs at zero temperature are obtained. Additionally, how the BCS equation for layered superconductors changes in the presence of SOIs is determined.

The electronic band structure of Weyl semimetals possesses pairs of linear band crossings, called Weyl nodes, characterized by opposite chirality charges associated with each node. The momentum space position of the nodes can reverse across a planar interface and these host Fermi-arc-like bound states, in addition to scattering states. We show that a magnetic interstitial layer can tune these states in three distinct ways. The electrostatic potential and one of the in-plane magnetic potential components control the shape of the bound state Fermi arcs. For moderate values of the same in-plane magnetic potential electrons are spin-filtered across the interface, while both the in-plane magnetic components and the electrostatic potential control the transmission of electrons. The ratio of in-plane to out-of-plane magnetic components can be used to turn on or turn off the magnetic potential effects, since the latter does not affect the interface states. The tunability arises from spin-momentum locking and chirality reversal at the interface. Thus, the effects can mix or interchange depending on the specific material but the states will remain tunable.

The electronic and magnetic properties of 3d-3d double perovskite oxides ${\mathrm{Ba}}_x{\mathrm{Sr}}_{2-x}{\mathrm{TiFeO}}_6$ (BSTF) have been studied using a combined experimental and theoretical approach. The magnetic behavior of ${\mathrm{Ba}}_x{\mathrm{Sr}}_{2-x}{\mathrm{TiFeO}}_6$ has been investigated by EPR spectroscopy (5 to 650 K), Mössbauer spectroscopy (78 to 300 K), and magnetometry (5 to 315 K). The temperature dependence of the EPR linewidth shows two minima for all samples (in the temperature range 100–200 K), implying structural changes in the local environment arising from the ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Fe}}^{4+}$ ions. The two types of iron ions ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Fe}}^{4+}$ are indicated by Mössbauer spectroscopy and their percentage in the samples were estimated. An antiferromagnetic phase transition is indicated by a negative Curie-Weiss temperature, which we found in our magnetic susceptibility studies with temperature by adjusting three distinct magnetic fields (0.1, 1, and 10 kOe) in ${\mathrm{Ba}}_x{\mathrm{Sr}}_{2-x}{\mathrm{TiFeO}}_6$, and these transition temperatures were also estimated. However, a type 5 ordered $\mathrm{Pm}\overline{3}\mathrm{m}$ structure with AFM-1 type alignment of spin moment on the two inequivalent Fe-1 and Fe-2 atoms has been found to be the magnetic ground state from density functional theory-based calculations. The coexistence of different charge states of Fe (${\mathrm{Fe}}^{3+}$ and ${\mathrm{Fe}}^{4+}$) has been validated from theoretical calculations. The exchange interaction calculations show a long-range antiferromagnetic ordering with a competing weak ferromagnetic interaction.

Topological phases of electrons such as topological insulators and quantum Hall states typically require strong spin-orbit coupling or magnetic fields. In this study, we consider an electron system coupled to a spin system, where electrons interact with magnons, i.e., quasiparticles of spin waves. We show that the interaction between electrons and magnons transfers the effect of symmetry breaking in the spin system to the electron system, whereby a nontrivial topological phase can be induced in the electron system that is otherwise topologically trivial. Through this “topology transfer” mechanism, we demonstrate the realization of various topological phases, including quantum Hall and quantum spin Hall insulators, in simple ferromagnetic spin systems, without requiring strong spin-orbit coupling or an external magnetic field for electron systems.

We investigate the single crystals of ${\mathrm{Ni}}_{0.19}{\mathrm{NbSe}}_2$, revealing that Ni intercalation profoundly alters the physical properties of ${\mathrm{NbSe}}_2$. Magnetic measurements clearly show that the system is magnetically frustrated with antiferromagnetic ordering below 23.5 K, with an irreversibility temperature near 10 K, and a magnetic hysteresis with a small net magnetic moment. Overall, the system can be described as an inhomogeneous antiferromagnetic phase with magnetic disorder and magnetic frustration. We found two Curie-Weiss temperatures of –80 K for the field in the $ab$ plane and –137 K for the field out of plane, which are a consequence of anisotropic interactions in spin space and favor an orientation of the spin along the $c$ axis. Temperature-dependent resistivity shows a complete suppression of both charge density waves and superconducting order down to 300 mK. Angle-resolved photoemission spectroscopy at 84 K reveals a $\overline{\mathrm{\Gamma }}$-centered electron pocket in ${\mathrm{Ni}}_{0.19}{\mathrm{NbSe}}_2$, which is absent in pristine ${\mathrm{NbSe}}_2$. The electronic structure results show a shift of the van Hove singularity (VHS), which is the main cause of the suppression of the electronic orders. These results align with recent theoretical predictions that Ni intercalation with cationic disorder favors frustrated antiferromagnetic stripe states, shifts the VHS and reconstructs the Fermi surface in ${\mathrm{NbSe}}_2$. Our findings position ${\mathrm{Ni}}_{0.19}{\mathrm{NbSe}}_2$ within a magnetically frustrated, nonsuperconducting regime, highlighting how partial intercalation and disorder drive complex magnetic order and the Fermi surface reconstruction in low-dimensional quantum materials.

The last several decades have seen significant advances in the theoretical modeling of materials within the fields of solid-state physics and materials science, but many methods commonly applied to this problem struggle to capture strong electron correlation accurately. Recent widespread interest in quantum materials—where strong correlation plays a crucial role in the quantum effects governing their behavior—further highlights the need for theoretical methods capable of rigorously treating such correlation. Here, we present a periodic generalization of variational two-electron reduced density matrix (2-RDM) theory, a bootstrapping-type method that minimizes the ground-state energy as a functional of the 2-RDM without relying on the wave function. The 2-RDM is computed directly by semidefinite programming with $N$-representability conditions, ensuring accurate treatment of strongly correlated electronic systems. By exploiting translational symmetry, we significantly reduce computational scaling, enabling applications to realistic materials-scale systems. Additionally, we introduce an alternative to conventional energy band structures: natural-orbital occupation-number bands, which, being independent of mean-field assumptions, offer deeper insights into electron correlation effects. We demonstrate the effectiveness of this approach by applying the theory to hydrogen chains, molybdenum disulfide, and nickel oxide, showing that natural-orbital occupation bands correctly capture electronic character in regimes where density functional theory fails. This work represents a major step toward accurately describing the electronic structure of quantum materials using reduced density matrices rather than wave functions.

Silicon is a pivotal material for modern electronics, but its indirect-gap nature makes it inefficient in band-to-band light emission. The realization of efficient light emission has epoch-making significance in the manufacturing of photonic chips and optical interconnect. Previous experimental studies have reported dislocation luminescence in silicon and constructed the related light-emitting devices. However, the light emission mechanism remains elusive. Here, based on large-scale first-principles calculations, we have studied the electronic structure and optical properties of different types of dislocations in silicon. It is found that the $〈110〉$ type-I edge dislocation shows a quasidirect band gap at the Γ point. The natures of the band edge states are not the dislocation states residing inside the core, rather they are bulklike states confined near the dislocation caused by strain induced by the dislocation. Due to the strong confinement, they have large optical transition dipole moments ($\sim 0.23\mathrm{eV}$), thus making them optically active. Furthermore, applying a small compressive strain ($\sim 0.5\%$) can easily change the band structure from quasidirect to direct, further enhancing the optical transition at the Γ point and improving the efficiency of the related Si-based optical devices. Finally, we also found two incognizant stable mixed-edge dislocation configurations.

We map the ground-state phase diagram of the quarter-filled spinless Su-Schrieffer-Heeger chain with nearest-neighbor interactions by combining exact diagonalization (ED) and density-matrix renormalization group (DMRG) under twist-averaged boundary conditions to suppress shell effects. A unified scaling analysis of the equal-time charge structure factor $S_{\mathrm{cdw}}\left(q\right)$—including the size dependence of $S_{\mathrm{cdw}}\left(q_{min}\right)$, the extrapolation of $S_{\mathrm{cdw}}\left(q_{min}\right)/L$ versus $1/L$, the evolution of $K_{\mathrm{eff}}\left(L\right)=\frac{1}{2}L{S}_{\mathrm{cdw}}\left(q_{min}\right)$, and the power-law behavior of $S_{\mathrm{cdw}}\left(2k_F\right)$—disentangles phase separation (PS), Luttinger liquids with pairing-dominated correlations ($K>1/2$), Luttinger liquids dominated by $2k_F$ bond-order-wave (BOW) correlations ($K<1/2$), and a long-range $2k_F$ charge-density-wave (CDW) phase. The phase structure, controlled by the interaction $V/t$ and dimerization $\delta t/t$, is as follows: PS for $V/t\lesssim -2$; a pairing-dominated Luttinger liquid for $-2<V/t<0$; for $V/t>0$ and moderate $|\delta t/t|$ the system realizes a $2k_F$-BOW-dominated Luttinger liquid; and for approximately $V/t\gtrsim 1.5$ together with $|\delta t/t|\lesssim 0.9$ it enters a long-range $2k_F$ CDW, whose domain expands toward smaller $|\delta t/t|$ with increasing $V/t$. Quantitative agreement between ED and DMRG across system sizes and boundary treatments underscores the robustness of this phase map and provides a benchmark for the competition between interactions and dimerization in one-dimensional dimerized chains.

$R\mathrm{SbTe}$ ($R$ = rare earth) compounds belong to the ZrSiS-type material family, characterized by a square lattice that hosts topological nonsymmorphic Dirac fermions and nodal-line fermions owing to its high crystalline symmetry. In this study, we investigate the structural and electrical properties of the nonmagnetic $R\mathrm{SbTe}$ compounds, LaSbTe and YSbTe, achieving precise control of their band fillings through a crystal growth technique that enables fine-tuning of the Te/Sb ratio. We show that, in the Te-rich region, both compounds crystallize in a high-symmetry tetragonal phase. In this phase, LaSbTe exhibits charge-density-wave order accompanied by a distortion into an orthorhombic lattice, consistent with previous reports. In the Sb-rich region of both compounds, the structure transforms into an orthorhombic phase with space group $P{2}_1{2}_1{2}_1$ (No. 19), featuring a distorted kite-shaped square lattice. This phase exhibits a narrow energy gap, which we attribute to remnants of the band crossings present in the tetragonal phase. We clarify the crystal structures including instabilities arising from high crystalline symmetry, electronic structures, and electrical properties. These findings provide a foundation for future studies of $R\mathrm{SbTe}$ systems, particularly on the interplay between nontrivial band topology and magnetism induced by lanthanide substitution.

Multiple charge density waves (CDWs) are observed in monolayer ${\mathrm{VTe}}_2$, but its modulated lattice and electronic structures remain less explored. Here, we identify $4\times 4$, $2\sqrt{3}$ $\times$ $2\sqrt{3}$, and related stripe CDW phases of monolayer ${\mathrm{VTe}}_2$ and clarify their relative stability using first-principles calculations. On top of a $4\times 4$ star-of-David (soD) phase showing unstable zone-center optical phonon modes, we find two lower-energy $4\times 4$ distorted soD phases, preserving (or breaking) threefold rotational symmetry and having nontrivial $Z_2$ = 1 (or trivial) band topology, with simulated scanning tunneling microscopy patterns agreeing with experiments on samples with corresponding symmetry. We confirm their metallic CDW behaviors with distinct $k$-resolved gapping characters, and reveal the possible superimposition of a $4\times 1$ stripe phase on the $4\times 4$ order. The $2\sqrt{3}$ $\times$ $2\sqrt{3}$ phase featuring a continuous pattern of truncated triangle-shaped V clusters is less stable in energy than $4\times 4$ phases, and behaves as a semimetal within semilocal functional, but as a small-gap semiconductor when including the nonlocal exchange interaction, in line with experiments. We further unravel the effects of charge doping and potential magnetic interactions on the energy sequence and precedence of different CDW phases. Our work provides important insights into the competing charge orders in monolayer ${\mathrm{VTe}}_2$, paving the way for future experiments and device designs.