The crystal structure used as an input to electronic structure calculation of conventionally bonded solids consists primarily of the standard crystallographic degrees of freedom. Quantum solids sometimes have additional microscopic degrees of freedom nested within the crystallographic structure. These might include local motifs including positional (Peierls dimers, deformed octahedra, and Jahn-Teller distortions), magnetic (local moment configurations), and dipolar (local ferroelectric configurations). Such motifs can be observed experimentally via local probes that avoid averaging and theoretically as distinct total energy-lowering features relative to more simplified average crystallographic structures. Here, we examine the ability of electronic structure methods independent of strong correlation physics to explain the broad phenomenology of metal-insulator selectivity in quantum oxides by energy-lowering symmetry breaking. We do this by avoiding the restriction of considering only (i) electron-electron interactions in a fixed unresponsive lattice—as done in Mott strong correlation explanations—allowing, however, (ii) local positional and magnetic motifs that coexist within a crystallographic landscape. We find, in a broad range of quantum oxides with different symmetry-breaking modes, the formation of split-off flat bands that can also control metallic vs insulating characteristics. The split-off band effect is common to magnetic and nonmagnetic materials, including both binary and ternary oxides. One finds that, when such local symmetry-breaking motifs are considered in mean-field-like (e.g., density functional theory) electronic structure calculations of quantum oxides, they explain many of the observed trends in metal vs insulator phases discussed otherwise in prior literature via strong correlation in symmetry-unbroken view.

We present a theoretical investigation of the Casimir-Lifshitz torque between black phosphorus and the liquid crystal material 4-cyano-4-n-pentylcyclohexane-phenyl. Employing quantum field theory methods, we derive an effective action that describes the optical properties of black phosphorus, based on a low-energy effective Hamiltonian. We obtain an analytical expression for the Fresnel matrix of the black-phosphorus-vacuum system by modifying Maxwell's equations. Our analysis reveals that the wavelength-dependent permittivity function plays a crucial role in the study of Casimir-Lifshitz torque in two-dimensional systems.

The intertwining of magnetism with topology is known to give rise to exotic quantum phenomena. Here, we explore the magnetotransport properties of NdAlSi, a magnetic Weyl semimetal that spontaneously breaks inversion and time-reversal symmetries and hosts a large number of Weyl nodes. We observe a significant negative magnetoresistance, which we attribute to the chiral anomaly associated with multiple Weyl nodes. Remarkably, the extracted chiral coefficient reaches approximately $52\mathrm{m}{\mathrm{\Omega }}^{-1}{\mathrm{m}}^{-1}{\mathrm{T}}^{-2}$, larger than many other topological materials. Additionally, we observe an exotic anomalous Hall effect with an out-of-sync behavior, where the anomalous Hall resistance does not exactly follow the field dependence of the magnetization, in contrast to that in conventional ferromagnets. These rich quantum transport phenomena, driven by the interplay between magnetism and Weyl nodes, establish NdAlSi as a prime platform for exploring the intricate topological behaviors of magnetic Weyl semimetals.

A quantum kinetic theory of the linear response to an electric field is provided from a controlled expansion of the Keldysh theory at leading order, for a multiband electron system with weak scalar disorder. The response is uniquely partitioned into intraband distribution functions and interband quantum coherences. A new explicit formula is provided for the latter, outlining their true nature as local dependent quantities, for which the mesoscopic gradients of the former are uncovered as a source term, opening a new research area. The precise connection with the Kubo formula in the ladder approximation is established. A pedagogical application to spin-orbit torque theory in the two-dimensional electron gas demonstrates the striking efficiency of the quantum kinetic approach. Some important implications for the theory of orbital transport are also briefly discussed.

The spin-orbit coupling (SOC) effect of heavy elements has the capacity to influence the electron structure and properties of materials. Previous studies have demonstrated that the SOC effect enhances the electron-phonon coupling constant (EPC λ) of elemental Pb and Pb-containing compounds in theory. However, the opposite phenomenon is found in the hydrides of lead that we studied, i.e., the SOC effect reduced the EPC λ. Moreover, previous studies have not clearly elucidated the underlying physical mechanism through which SOC effects impact superconductivity. Furthermore, the effects of SOC in Pb-H compounds under high pressure remain unexplored. Here, we investigated the structures of the Pb-H system and the EPC mechanism under the action of SOC at pressures. A new $P{2}_1/m\text{−}\mathrm{Pb}{\mathrm{H}}_2$ hydride has been discovered to be more stable under high pressure than previously reported. The new lead superhydrides have been identified, including Cmcm-$\mathrm{Pb}{\mathrm{H}}_{10}$, which contains a linear ${\mathrm{H}}_4$ macromolecule with double covalent bonds. The superconducting critical temperature ($T_c$) of lead superhydrides is significantly lower than that of $\mathrm{Y}{\mathrm{H}}_{10}$ and $\mathrm{La}{\mathrm{H}}_{10}$. This is due to the fact that hydrogen exists in the form of a large number of ${\mathrm{H}}_2$ molecules without forming a cagelike supramolecular structure. In Pb, in addition to the previously reported reason of phonon softening, we have identified another important factor contributing to the increase in EPC λ: the enhancement of the average electron-phonon interaction at the Fermi surface due to the SOC effect. In Pb-H compounds, the SOC effect leads to the topological transformation of the Fermi surface, and increases the probability of charges appearing near H-H bonds and the twisting vibration frequency of hydrogen molecules, which is the important reason for the decline of EPC λ. In the Pb-H system, the SOC effect can result in an increase in the average phonon frequency and a decrease in EPC λ. The superconducting $T_c$ is dependent upon the competition between the decreased EPC λ and the increased Debye temperature.

${\mathrm{As}}_{20}{\mathrm{Se}}_{80}$ glass $\left(\mathrm{g}\text{−}{\mathrm{As}}_{20}{\mathrm{Se}}_{80}\right)$ was studied under static high pressure using in situ Raman spectroscopy, x-ray diffraction, and electrical measurements. With increasing pressure, g-${\mathrm{As}}_{20}{\mathrm{Se}}_{80}$ shows a breakdown of intermediate-range ordering around 6 GPa and then becomes metallic above 9 GPa. It subsequently undergoes a pressure-induced crystallization, towards the $\beta$-Po-type crystal structure ($\mathrm{c}\text{−}{\mathrm{AsSe}}_4$ phase), above 20 GPa. Crystalline $\mathrm{c}\text{−}{\mathrm{AsSe}}_4$ remains in this structure up to at least 35 GPa. This structure is identical with the one observed for pure c-Se, albeit at much higher pressures. The pressure-induced metallization and crystallization are fully reversible upon pressure release, with considerable hysteresis. The results are discussed in comparison with the general structural phase diagram of c-Se under pressure and the implication of pressure-induced crystallization towards understanding the nature of the glass transition.

We present measurements on ${\mathrm{Fe}}_2{\mathrm{O}}_3$ amorphization and melt under laser-driven shock compression up to 209(10) GPa via time-resolved in situ x-ray diffraction. At 122(3) GPa, a diffuse signal is observed indicating the presence of a noncrystalline phase. Structure factors have been extracted up to 182(6) GPa showing the presence of two well-defined peaks. A rapid change in the intensity ratio of the two peaks is identified between 145(12) and 151(12) GPa, indicative of a phase change. The noncrystalline diffuse scattering is consistent with shock amorphization of ${\mathrm{Fe}}_2{\mathrm{O}}_3$ between 122(3) and 145(12) GPa, followed by an amorphous-to-liquid transition above 151(12) GPa. Upon release, a noncrystalline phase is observed alongside crystalline $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$. The extracted structure factor and pair distribution function of this release phase resemble those reported for ${\mathrm{Fe}}_2{\mathrm{O}}_3$ melt at ambient pressure.

Recent experimental and theoretical developments in the quantum Hall effect in monolayer graphene showed that the previous model of the valley-anisotropy interaction is incomplete, as it was assumed to be ultrashort range (USR). In this work, we use exact diagonalization to go beyond the ultrashort range to find the different phases for $\nu =2/3$. We model the interaction as Yukawa so that we can control the range as a proof of concept. Even in this simple setting, we discovered how dropping the USR condition shifts the transition borders in favor of certain phases, leads to a new bond-ordered phase appearing, and breaks the ferromagnetic phase in two competing states as a result of lifting the USR-driven degeneracy.

The account of simulations using a tried and tested code of resonant x-ray scattering (fdmnes) is incomplete or incorrect. Notwithstanding, they are not faithful representations of the established structure of alpha-${\mathrm{U}}_2{\mathrm{N}}_3$.

In our paper [Phys. Rev. B 110, 125138 (2024)], we present the results of a series of anisotropic resonant x-ray scattering experiments conducted on epitaxial films of low-symmetry uranium compounds (${\mathrm{U}}_2{\mathrm{N}}_3$ and ${\mathrm{U}}_3{\mathrm{O}}_8$). We observed a temperature-independent resonant signal at the uranium $M_4$ absorption edge at weak and forbidden reflections. By utilizing the fdmnes code, we demonstrate that these results stem from the aspherical charge distributions of $5f$ electrons around the uranium nucleus. For ${\mathrm{U}}_2{\mathrm{N}}_3$, where uranium atoms occupy two distinct sites of differing symmetry, labeled ${\mathrm{U}}_1$ and ${\mathrm{U}}_2$, we find that the contribution to resonant scattering from ${\mathrm{U}}_1$ is significantly smaller than that from ${\mathrm{U}}_2$, yet it is not negligible. In his Comment [Phys. Rev. B 111, 037101 (2025)], Lovesey argues that atoms located at the ${\mathrm{U}}_1$ site should contribute zero to the scattering due to symmetry constraints. Here, we clarify that this assertion is incorrect.

The existence of exotic singularities in momentum space, such as spin-1 excitations and Rarita-Schwinger-Weyl (RSW) fermions, has been discussed so far to explore unique phenomena in the nonmagnetic B20-type compounds. Meanwhile, the nonlinear chiral thermoelectric (NCTE) charge and thermal Hall effects, responses proportional to the cross product of the electric field and the temperature gradient, are expected in the chiral materials, yet remain unexplored in B20-type compounds. Here, based on ab initio calculations and symmetry analysis, we quantitatively analyze the NCTE charge and thermal Hall effects in cobalt monosilicide, obtaining experimentally measurable values of the NCTE charge and thermal Hall currents along the [111] direction, which is not expected for second-order current responses to the dc electric field. Furthermore, we demonstrate that these significant responses are enhanced around RSW fermions and spin-1 excitations. Additionally, we clarify that the NCTE Hall effect is solely governed by orbital magnetic moments due to the cancellation of Berry curvature contributions in cubic chiral crystals.

The magnetic topological phases attract much interest, such as the axion insulator, higher-order topology, Weyl semimetals, and the quantum anomalous Hall effect (QAHE). Here, we predict that the axion insulator phase, magnetic Weyl points, and QAHE can be achieved in ${\mathrm{Eu}}_3{\mathrm{In}}_2{\mathrm{As}}_4$. Recently, single-crystal ${\mathrm{Eu}}_3{\mathrm{In}}_2{\mathrm{As}}_4$ was successfully synthesized, and it exhibits an antiferromagnetic (AFM) ground state. Our first-principles calculations show that it lies on the phase boundary between multiple magnetic topological phases, and the magnetic anisotropy is weak, with an energy difference less than 1 meV. In the AFM state, it can be tuned to an axion insulator by tensile strain. The quantized axion angle $\theta =\pi$ and the magnetic higher-order topology are characterized by the parity index $Z_4=2$. By applying an external magnetic field, the induced ferromagnetic (FM) state becomes an ideal magnetic topological semimetal with a single pair of Weyl points or a nodal ring. The QAHE can be achieved in FM multilayer films of ${\mathrm{Eu}}_3{\mathrm{In}}_2{\mathrm{As}}_4$ on a magnetic insulating substrate.

In few-qubit systems, the quantum Zeno effect arises when measurement occurs sufficiently frequently that the spins are unable to relax between measurements. This can compete with Hamiltonian terms, resulting in interesting relaxation processes which depend nonmonotonically on the ratio of measurement rate to coherent oscillations. While Zeno physics for a single qubit is well understood, an interesting open question is how the Zeno effect is modified by coupling the measured spin to a nontrivial bulk. In this work, we study the effect of coupling a one-dimensional transverse field Ising to a Zeno spin which lives at the boundary. We find that sharp singularities occur in the boundary relaxation dynamics, which can be tied to the emergence or destruction of edge modes that can be found analytically. Finally, we provide numerical indications that the dynamical singularities are stable in the presence of integrability-breaking interactions.

Optically detected magnetic resonance (ODMR) is a useful technique for studying interactions between local spins (magnetic ions) and the carrier gas. We present an ODMR study of a single $\left(\text{Cd}\text{,}\text{Mn}\right)\text{Te}/\left(\text{Cd}\text{,}\text{Mg}\right)\text{Te}$ quantum wells (QWs) with the hole gas. We observe different characteristics of the ODMR signals obtained simultaneously using the optical signals of the neutral and positively charged exciton. From this, we infer the existence of local fluctuations of carrier gas density resulting in separate populations of ${\mathrm{Mn}}^{2+}$ ions. At the same time, the shape of the ODMR signal contains information about the temperature of the magnetic ions involved in the absorption of the microwaves. Studying it in detail provides even more information about the interactions with charge carriers. In the QW, two separate ensembles of ions are thermalized differently in the presence of carriers.

Raman spectroscopy is a valuable characterization tool for two-dimensional materials. Starting from model Hamiltonians for Chern insulators and magnetized monolayers of transition-metal dichalcogenides, we theoretically predict two unconventional features of Raman spectroscopy. First, a selection rule emerges in the Raman tensor when the incident and scattered photons are circularly polarized. This rule generalizes the well-known valley selection rule of optical conductivity in Dirac insulators. Second, for an electronic model with a single massive Dirac fermion, the phase difference between Raman tensor elements is quantized to $\pm \pi /2$ for any frequency of the incident light. The quantization is robust under perturbations and the sign of the phase difference is reversed when the mass term of the Hamiltonian is inverted.

The discovery of a charge density wave (CDW) in the antiferromagnetic kagome metal FeGe has prompted interest in the interplay between kagome physics, CDW, and magnetism. However, a crucial aspect for understanding these emergent phenomena—the precise CDW structure—remains ambiguous. Recent studies have assumed uniformly distributed Ge dimers, but this assumption is problematic. The predicted band structure based on this model exhibits an abrupt disappearance of a Ge $p$ band in the Fermi surface, contradicting experimental observations from angle-resolved photoemission spectroscopy (ARPES). In this paper, we propose that a CDW phase with disordered Ge dimers can reconcile theoretical predictions with ARPES results. This model reproduces the observed CDW gaps while preserving the Ge $p$ band. Depending on experimental conditions, Ge dimers can be randomly distributed or exhibit phase separation from pristine regions. Our findings reveal the crucial role of Ge dimer disorder in the FeGe CDW and suggest potential implications of this disorder for other properties, such as magnetism and transport, in this system.

Most periodic systems are governed by short-range interactions as long-range interactions in these systems diminish uniformly. In this Letter, however, we demonstrate that this is not true for a more general class of systems, which possess long-range order without periodicity, known as quasiperiodic systems. Quasiperiodicity alters the well-known characteristics of the long-range couplings, resulting in anomalous enhancement for arbitrarily long distances, even beyond the mesoscopic scale. By exemplifying the indirect spin exchange interaction, we show that the long-range coupling in a quasiperiodic chain does not attenuate over distance but is instead governed by a distance metric, we have named the hyperspace geometric distance. This enables us to remotely control the spins over even mesoscopic distances. Our work provides new paradigms of strongly correlated physics applicable to a broader class of systems beyond the conventional ones.

We show that magnetic insulators with a collinear and compensated order can exhibit a thermal Hall effect even at zero magnetic field if they have altermagnetic symmetries. We predict a finite thermal Hall conductivity vector ${\mathit{\kappa }}_{\text{H}}$ for a rutile-inspired effective spin model with Dzyaloshinskii-Moriya interaction. Within the linear spin-wave theory, we identify two magnon branches that carry identical Berry curvature and give rise to a finite ${\mathit{\kappa }}_{\text{H}}$, which can be controlled by the Néel vector orientation and by strain. The thermal Hall response is further complemented with a spin Nernst response to contrast spin and heat transport in altermagnetic insulators with those in ferromagnets and antiferromagnets. Our results establish the crystal thermal Hall effect of magnons and we discuss material candidates for experimental realization, such as ${\mathrm{MnF}}_2, {\mathrm{CoF}}_2$, and ${\mathrm{NiF}}_2$.