The crystal and magnetic structures of van der Waals layered antiferromagnet $\mathrm{Cr}{\mathrm{Cl}}_3$ have been studied using x-ray and neutron powder diffraction at pressures up to 15 GPa at ambient temperature and up to 2 GPa in a temperature range 7–300 K, respectively. The vibrational properties of $\mathrm{Cr}{\mathrm{Cl}}_3$ were studied using Raman spectroscopy at pressures up to 28 GPa at ambient temperature. Application of high pressure leads to a gradual structural phase transition from the monoclinic $C2$/m to rhombohedral $R\overline{3}$ structure developed in the pressure range of 1–6 GPa at ambient temperature. It is accompanied by anomalies in the pressure behavior of lattice parameters, unit cell volume, and vibrational modes. Upon compression above 1 GPa at low temperatures, the initial A-type antiferromagnetic state becomes suppressed, and the ferromagnetic state is formed below Curie temperature $T_{\mathrm{C}}\sim 19$ K. The microscopic nature of the pressure-induced AFM–FM magnetic phase transition in bulk $\mathrm{Cr}{\mathrm{Cl}}_3$ is different from those found in bilayer $\mathrm{Cr}{\mathrm{I}}_3$. These findings clarify, in detail, a response of structural and magnetic states in a model $\mathrm{Cr}{\mathrm{Cl}}_3$ system with the AFM ground state on variation of thermodynamic parameters and provide important information for further development of theoretical models describing physical properties of chromium trihalides and related van der Waals materials in bulk and few-layered forms.

The key concept of mobility edge, which marks the critical transition between extended and localized states in the energy domain, has attracted significant interest in the cutting-edge frontiers of modern physics due to its profound implications for understanding localization and transport properties in disordered systems. However, a generic way to construct multiple mobility edges (MME) is still ambiguous and lacking. In this work, we propose a brief scheme to engineer both real and complex exact multiple mobility edges exploiting a few coupled one-dimensional quasiperiodic chains. We study the extended-localized transitions of coupled one-dimensional quasiperiodic chains along the chain direction. The model combines both the well-established quasiperiodicity and a kind of freshly introduced staggered nonreciprocity, which are aligned in two mutually perpendicular directions, within a unified framework. Based on analytical analysis, we predict that when the couplings between quasiperiodic chains are weak, the system will be in a mixed phase in which the localized states and extended states coexist and intertwine, thus lacking explicit energy separations. However, as the interchain couplings increase to a certain strength, exact multiple mobility edges emerge. This prediction is clearly verified by concrete numerical calculations of the fractal dimension $FD$ and the scaling index $\beta$. Moreover, we show that the combination of quasiperiodicity and the staggered nonreciprocity can be utilized to design and realize quantum states of various configurations. Our results reveal a brief and general scheme to implement exact multiple mobility edges for synthetic materials engineering.

We study universal chaotic dynamics of a large class of periodically driven critical systems described by spatially inhomogeneous conformal field theories. By employing an effective curved spacetime approach, we show that the onset of quantum chaotic correlations, captured by the Lyapunov exponent of out-of-time-order correlators (OTOCs), is set by the effective temperature of emergent Floquet horizons. Furthermore, scrambling of quantum information is shown to be strongly inhomogeneous, leading to transitions from chaotic to nonchaotic regimes by tuning driving parameters. We finally use our framework to propose a concrete protocol to simulate and measure OTOCs in quantum simulators, by designing an efficient stroboscopic backward time evolution.

A quantum battery is a quantum mechanical storage device that enables fast charging and higher-energy densities, surpassing classical limits. We demonstrate an enhanced charging performance in nonreciprocal quantum batteries (QBs) featuring unidirectional coherent couplings in multimode bosonic systems. Crucially, a multimode nonreciprocal quantum battery achieves a speedup and quadratic scaling advantage in charging dynamics, a dramatic improvement over both single-mode systems and reciprocal multimode architectures. More precisely, fast charging dynamics occur under symmetrically matched local dissipation rates, whereas a quadratic scaling emerges under identical global dissipation rates. Our findings establish multimode nonreciprocity as a transformative resource for quantum energy technologies, with implications for energy capture, storage, and conversion in quantum devices.

Thermally induced spin transition materials are known for their potential applications in a wide range of fields, from pressure and strain sensing to high-density information storage and control. The latter are described by Ising-like models and elaborate elastic theories including the coupling between the change of spin state and the accompanying local deformation of the lattice during the transition. In the present work, the Morse potential is used to model interactions between spin-transition molecules. The resultant Hamiltonian is solved by searching first for the mechanical equilibrium, revealing an isomorphism with an Ising-like model, including competing short- and long-range interactions with the presence of anharmonic effects. Studies within the molecular field approximation, Bethe-Peierls, and Monte Carlo methods allow reproducing several experimental situations among which gradual, first-order, and two-step transitions are observed, demonstrating the ability of the model to capture the diversity of spin-crossover materials while comparing the different methods and their limitations.

The interplay between ferroelectricity, magnetism, and superconductivity provides a rich platform for discovering novel quantum phenomena. Here, we develop an effective theory and propose a heterostructure composed of an antiferromagnetic bilayer ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ coupled with the $s$-wave superconductor Fe(Se,Te), enabling the realization of chiral topological superconductivity (CTSC) with switchable chirality. The chirality of the CTSC is controlled by the direction of spontaneous polarization, which arises from interlayer sliding-induced ferroelectricity or charge transfer in the bilayer ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$. This sliding mechanism breaks the ${\mathcal{M}}_z\mathcal{T}$ and $\mathcal{PT}$ symmetries, leading to the anomalous Hall effect in the spin-polarized metallic Dirac band and drives the emergence of CTSC when the $s$-wave superconductivity appears. Our work not only provides a pathway to achieve and control topological superconductivity but also opens avenues for experimental exploration of Majorana physics and topological quantum computation.

We show how graph theory concepts can provide an insight into the origin of slow dynamics in systems with kinetic constraints. In particular, we observe that slow dynamics is related to the presence of strong hierarchies between nodes on the Fock-space graph in the particle occupation basis, which encodes configurations connected by a given Hamiltonian. To quantify hierarchical structures, we develop a measure of centrality of the nodes, which is applicable to generic Hamiltonian matrices and inspired by established centrality measures from graph theory. We illustrate these ideas in the quantum East (QE) model. We introduce several ways of detuning nodes in the corresponding graph that alter the hierarchical structure, defining a family of QE models. We numerically demonstrate how these detunings affect the degree of nonergodicity on finite systems, as evinced by both the time dependence of density autocorrelations and eigenstate properties in the detuned QE models.

A characteristic property of a gapless liquid state is its emergent symmetry and dual symmetry, associated with the conservation laws of symmetry charges and symmetry defects respectively. These conservation laws, considered on an equal footing, cannot be described simply by the representation theory of a group (or a higher group). They are best described in terms of a topological order (TO) with a gappable boundary in one higher dimension; we call this the symTO of the gapless state. The symTO can thus be considered a fingerprint of the gapless state. We propose that a largely complete characterization of a gapless state, up to local low-energy equivalence, can be obtained in terms of its maximal emergent symTO. In this paper, we review the symmetry/topological-order (Symm/TO) correspondence and propose a definition of maximal symTO. We discuss various examples to illustrate these ideas. We find that the $1+1\text{D}$ Ising critical point has a maximal symTO described by the $2+1\text{D}$ double-Ising topological order. We provide a derivation of this result using symmetry twists in an exactly solvable model of the Ising critical point. The critical point in the three-state Potts model has a maximal symTO of double-(6,5)-minimal-model topological order. As an example of a noninvertible symmetry in $1+1\text{D}$, we study the possible gapless states of a Fibonacci anyon chain with emergent double-Fibonacci symTO. We find the Fibonacci-anyon chain without translation symmetry has a critical point with unbroken double-Fibonacci symTO. In fact, such a critical theory has a maximal symTO of double-(5,4)-minimal-model topological order. We argue that, in the presence of translation symmetry, the above critical point becomes a stable gapless phase with no symmetric relevant operator.

We study the low-energy spectrum of a single hole confined in a planar Ge quantum dot (QD) within the effective-mass formalism. The QD is sandwiched between two GeSi barriers of finite potential height grown along the [001] direction. To treat this finite barrier problem, we adopt an independent-band approach in dealing with the boundary conditions. The effects of different system parameters are investigated, including the width of the out-of-plane confining well, the size of the dot, and silicon concentration in the confining layers. The more accurate finite-barrier model results in a nontrivial dependence of the anisotropic $g$ factor on the silicon concentration in the barrier, and the choice of boundary conditions can have a non-negligible impact on its predicted value. On the other hand, the corresponding $g$ factor predicted by the hard-wall model only depends on the silicon concentration monotonically. The comparison shows that the hard-wall model falls short in capturing the interplay between strain and band offset. Furthermore, while the ideal model of a planar dot with a square-well heterostructure already has an intrinsic spin-orbit coupling, realistic effects arising from the experimental setup may give rise to additional contributions. We investigate the impact of the top-gate electric field and the residual tensile strain on the qubit states. The results indicate that these effects are important contributions to the total spin-orbit coupling, which enables fast electric control.

We discuss the microscopic modeling of exchange interactions between double semiconductor quantum dots used as spin qubits. Starting from a reference full configuration interaction (CI) calculation for the two-particle wave functions, we build a reduced basis set of dressed states that can describe the ground-state singlets and triplets over the whole operational range with as few as 100 basis functions (as compared to a few thousands for the full CI). This enables fast explorations of the exchange interactions landscape as well as efficient time-dependent simulations. We apply this methodology to a double hole quantum dot in germanium and discuss the physics of exchange interactions in this system. We show that the net exchange splitting results from a complex interplay among interdot tunneling, Coulomb exchange, and correlations. We analyze, moreover, the effects of confinement, strains, and Rashba interactions on the anisotropic exchange and singlet-triplet mixings at finite magnetic field. We finally illustrate the relevance of this methodology for time-dependent calculations on a singlet-triplet qubit.

Material systems with lone pair electrons have long been a treasure trove in the search for large second harmonic generation effects. Revealing the origin of second harmonic generation in nonlinear optical materials can provide theoretical guidance for the design of new materials. In this work, the origin of second harmonic generation in noncentrosymmetric materials containing lone pair electrons is revealed by analyzing the orbital interactions on the sublattice. Stereochemically inactive Pb $6s$ orbitals with high symmetry in ${\mathrm{CsPbCO}}_3\mathrm{F}$ contribute less to the second harmonic generation. In contrast, the contribution of stereochemically active Pb $6s$ orbital in ${\mathrm{PbB}}_5{\mathrm{O}}_7{\mathrm{F}}_3$ and ${\mathrm{PbB}}_2{\mathrm{O}}_3{\mathrm{F}}_2$ is more obvious. Significantly, the orbitals of the interaction between lead and oxygen make a very significant contribution because these orbitals are located at the band edge and in noncentrosymmetric sublattices.

We demonstrate the existence of a universal phase diagram of quantum chains with range-$k$ interactions subject to the conservation of a total charge and its dipole moment. These systems exhibit “freezing” transitions between strongly and weakly Hilbert-space-fragmented phases as the charge filling $\nu$ is varied. We show that these continuous phase transitions occur at a critical charge filling of ${\nu }_c={(k-2)}^{-1}$ independently of the on-site Hilbert-space dimension $d$. To this end, we analytically prove that, for any $d$, any state with $\nu <{\nu }_c$ hosts a finite density of sites belonging to “blockages,” which we define as subregions of the chain across which transport of charge and dipole moment cannot occur. Some blockages arise from sequences of frozen sites, i.e., sites with an unchanging on-site charge, while others do not involve frozen sites at all. We prove that the presence of blockages implies strong fragmentation of typical symmetry sectors into Krylov subspaces, each of which forms an exponentially vanishing fraction of the total sector. By studying the distribution of blockages we analytically characterize how typical states are subdivided into dynamically disconnected local “active bubbles” and prove that typical eigenstates at these charge fillings exhibit area-law entanglement entropy, while there exist rare eigenstates featuring non-area-law scaling. We also numerically show that for $\nu >{\nu }_c$ and arbitrary $d$, typical symmetry sectors are weakly fragmented, with their dominant Krylov sectors constituted of states that are free of blockages. We analytically derive some critical exponents characterizing the transition and numerically determine the density of blockages at $\nu ={\nu }_c$, with clear implications for transport at the critical point. Finally, we investigate the properties of special-case models for which no phase transitions occur.

The non-Hermitian skin effect (NHSE), a hallmark of non-Hermitian systems, stems from the topological nature of complex energy spectra, typically characterized by a nonzero spectral winding number. Beyond the spinless frameworks considered so far, here we realize a generic, tunable spinful NHSE in a one-dimensional (1D) tight-binding lattice endowed with spin-dependent Abelian gauge fields. With proper tuning of the gauge parameter, we uncover an emergence of bidirected, spin-polarized zero-winding skin states, appearing in the absence of transpose-type time-reversal symmetry (${\mathcal{TRS}}^{†}$) and featuring scale-restricted localization with non-Bloch spectral stability. While clearly distinct from the known ${\mathbb{Z}}_2$ and critical NHSEs, these unconventional skin states evolve into them upon enforcing ${\mathcal{TRS}}^{†}$ and introducing interspin coupling via magnetic fields, respectively. The magnetic field further drives a transition from a bidirectional to a unidirectional skin configuration. Our work unifies the previously known zero-winding NHSEs within a broader framework and provides experimentally accessible routes for realization in photonic and ultracold atomic systems with synthetic gauge fields.

${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$, a quasi-2D ferrimagnetic nodal-line semiconductor with $T_{\mathrm{c}}=78$ K, exhibits strongly angular-dependent colossal magnetoresistance (CMR) in its magnetically ordered state, which is featured by the development of a unique metallic state under magnetic fields along the $c$ axis. Recently, a peculiar chiral orbital current (COC) state has been proposed to exist in this compound, evidenced by the effective manipulation of magnetotransport properties via applying electrical currents. A field-induced insulator-to-metal transition (IMT) and field-controlled electron scattering off COC domain boundaries thus serve as two feasible origins of the CMR in ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$. Here, we further explore the current- and field-driven variations of electronic states in ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$ by scrutinizing its electrical transport, thermoelectric, and thermal transport properties. A combination of $I\text{−}V$ characteristics and Ettingshausen effect studies allows us to pinpoint the predominant impact of Joule heating on triggering the current-induced IMT. Measurement of the Seebeck effect unambiguously reveals a reduction of the band gap occurring concomitantly with the CMR, in accordance with the field-driven IMT scenario. A remarkable enhancement of thermal conductivity below $T_{\mathrm{c}}$ is observed when magnetic field is applied along $c$ but is absent under in-plane magnetic fields. Such an anisotropic positive magnetothermal conductivity most likely reflects increase of the phonon mean free path stemming from the field-induced suppression of boundary scattering, hence it implies the presence of certain types of field-tunable structural domain walls in ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$. Our findings not only underscore the intricate interplay between the spin, charge, and lattice degrees of freedom in ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$, but also point toward cooperative mechanisms for its CMR: Whereas the field-driven IMT appears to be the most essential cause, domain boundary scattering may still play a secondary role.

Revealing the electronic and magnetic properties of the parent compounds of high-$T_c$ superconductors is a crucial step in understanding unconventional superconductivity. Transport property measurements provide a widely accessible approach to this goal. However, gaining detailed quantitative information from transport experiments often requires a combination of different electric and thermoelectric characterizations as a function of several tuning parameters including magnetic field, temperature, and level of disorder. This is the case of the parent compounds of iron-based superconductors, whose electronic structure is characterized by multiple bands contributing to transport. In this study, we develop an analytical framework for the electric and thermoelectric properties of LaFeAsO by modulating its disorder through neutron irradiation. We demonstrate that, in the low-temperature phase, transport is governed by an $n$-type band with Dirac dispersion. These Dirac states could bear relevant information about the roles of antiferromagnetic and nematic fluctuations in the superconducting pairing mechanism. Additionally, we establish a protocol for identifying Dirac cones in the transport properties, which can be applied to the investigation of other fascinating systems, such as Dirac and Weyl semimetals.