Sliding ferroelectricity is induced by the artificial stacking of two-dimensional materials, and with specific stacking sequences, it can even emerge in nonferroelectric layered systems. Here, based on first-principles calculations, we demonstrate that multilayer black phosphorus (BP) with layer number $N\ge$ 3 exhibits ferroelectricity. The polarization originates from symmetry breaking induced by layer stacking and can be reversed through the relative sliding of adjacent layers. With an increasing number of layers, a greater diversity of polarization states emerges, highlighting the crucial role of layer number and interlayer dipole coupling in sliding ferroelectricity. Surface-layer displacement in BP slabs also generates spontaneous polarization, offering opportunities for experimental detection and manipulation. Our work establishes interlayer sliding as an effective approach to induce ferroelectricity in elemental multilayers, opening new possibilities for nonvolatile memory applications.

With a wide band gap and $p$-type dopability, cuprous delafossite compounds $\mathrm{Cu}M{\mathrm{O}}_2$ ($M$ = Al, Ga, In) are potential candidate materials for various optoelectronic applications. Nevertheless, the band structures of $\mathrm{Cu}M{\mathrm{O}}_2$ are not well established from both experimental and theoretical perspectives. In this paper, the electronic band structures of $\mathrm{Cu}M{\mathrm{O}}_2$ are investigated by using the all-electron $\mathit{GW}$ method with the linearized augmented plane-wave (LAPW) basis extended by high-energy local orbitals (HLOs). The inclusion of HLOs is found to have significant effects on the quasiparticle (QP) band structures of $\mathrm{Cu}M{\mathrm{O}}_2$, which opens the QP gap and corrects the artifacts in dispersion of conduction QP band owing to the incompleteness of the commonly used LAPW basis. The valence density of states are consistent with the energy distribution curves from photoelectron spectroscopy. Furthermore, we estimate the optical gaps by combining the direct QP gap at the L point and the exciton binding energy from $GW+$Bethe-Salpeter equation (BSE) calculations in the literature. This treatment gives optical gap of ${\mathrm{CuInO}}_2$ in good agreement with the absorption measurements, but overestimates the reported experimental data by about 0.5 eV for ${\mathrm{CuAlO}}_2$ and ${\mathrm{CuGaO}}_2$. We also evaluated the zero-point renormalization (ZPR) resulting from the electron-phonon coupling (EPC) based on the Fröhlich model, and found that ZPR reduces the fundamental band gaps of $\mathrm{Cu}M{\mathrm{O}}_2$ by about 0.2–0.3 eV. Although greatly improved agreement between theory and experiment can be achieved through enhancing numerical accuracy in $GW$ implementation and considering the EPC contribution, there remain significant discrepancies, which calls for in-depth scrutiny both experimentally and theoretically.

We investigate the phenomenon of correlated emission lasing in a coherently driven single quantum dot coupled to a bimodal photonic crystal cavity, utilizing a master equation to describe the system dynamics. To account for exciton-phonon interactions, we incorporate a nonperturbative approach through a polaron transformed master equation. By analyzing fluctuations in the Hermitian operators associated with relative and average phase, we derive a Fokker-Planck equation to assess phase drift and diffusion coefficients, demonstrating that correlated emission suppresses quantum noise in the presence of exciton-phonon interaction at low temperature. Additionally, we calculate the single- and two-photon excess emission rates (difference between emission and absorption rates) into the cavity modes and explore the generation of continuous-variable entanglement between these modes.

Ultrafast optical control of magnetism is a vibrant field in which femtosecond laser pulses are used to tune, manipulate, and enhance material magnetic properties. In this work, we induce ferromagnetism above ${\mathrm{T}}_{\mathrm{Curie}}$ by utilizing the coupling between spin and electrons in ${\mathrm{CrGeTe}}_3$. We suggest that the optical excitation electrons in ${\mathrm{CrGeTe}}_3$ induces a transition from a short-range to long-range magnetic ordering. We discuss the relation of the transition to the magnetic anisotropy of ${\mathrm{CrGeTe}}_3$ and the similarities of the photoinduced magnetism to cases where ${\mathrm{T}}_{\mathrm{Curie}}$was enhanced in ${\mathrm{CrGeTe}}_3$ by means of electrostatic gating, chemical doping, and hydrostatic pressure.

Characterizing the nature of many-body localization transitions (MBLTs) and their potential critical behaviors has remained a challenging problem. In this work, we study the dynamics of the displacement, quantifying the spread of the radial probability distribution in the Fock space, for three systems with MBLTs, i.e., the Hamiltonian models with quasiperiodic and random fields, as well as a random-circuit Floquet model of a MBLT. We then perform a finite-size scaling analysis of the long-time averaged displacement by considering two types of ansatz for MBLTs, i.e., continuous and Berezinskii-Kosterlitz-Thouless (BKT) transitions. The data collapse based on the assumption of a continuous phase transition with power-law correlation length reveals that the scaling exponent of the MBLT induced by random field is close to that of the Floquet model, but significantly differs from the quasiperiodic model. Additionally, we find that the BKT-type scaling provides a more accurate description of the MBLTs in the random model and the Floquet model, yielding larger (finite-size) critical points compared to those obtained from power-law scaling. Our work highlights that the displacement is a valuable tool for studying MBLTs, and is relevant to ongoing experimental efforts.

We develop an analytical approach to the spectral form factor and out-of-time ordered correlators in zero-dimensional Brownian models of quantum chaos. The approach expresses these spectral correlations as part of a closed hierarchy of differential equations that can be formulated for all system sizes and in each of the three standard symmetry classes (unitary, orthogonal, and symplectic, as determined by the presence and nature of time-reversal symmetry). The hierarchy applies exactly, and in the same form, to Dyson's Brownian motion and all systems with stochastically emerging basis invariance, where the model-dependent information is subsumed in a single dynamical timescale whose explicit form we also establish. We further verify this universality numerically for the Brownian Sachdev-Ye-Kitaev model, for which we find perfect agreement with the analytical predictions of the symmetry class determined by the number of fermions. This results in a complete analytical description of the spectral correlations and allows us to identify which correlations are universal in a large class of models.

We report the systematic synthesis, crystal structure, magnetization, and powder neutron diffraction of single-crystalline and polycrystalline ${\mathrm{CaCo}}_2{\mathrm{TeO}}_6$ samples. ${\mathrm{CaCo}}_2{\mathrm{TeO}}_6$ crystallizes in an orthorhombic structure with $Pnma$ space group, featuring chains of edge-shared ${\mathrm{CoO}}_6$ octahedra arranged in a honeycomb pattern. Two antiferromagnetic transitions are observed at $T_{N1}=14.4\mathrm{K}$ and $T_{N2}=16.2\mathrm{K}$, corresponding to two long-range magnetic orders with propagation vectors of ${\mathbf{k}}_1=(0,0,0)$ and ${\mathbf{k}}_2=(0.125,0,0.25)$, respectively. The ground state is determined as a canted up-up-down-down zigzag spin configuration along the $c$ axis, wherein the magnetic moments of Co1 and Co2 ions are $3.4\left(1\right){\mu }_B$ and $2.1\left(1\right){\mu }_B$, respectively. Successive spin-flop transitions appear with the increasing magnetic field applied along the easy axis ($c$ axis), accompanied by depression of the antiferromagnetic orders and enhancement of residual magnetic entropy. The field-induced spin-disordered state suggests that ${\mathrm{CaCo}}_2{\mathrm{TeO}}_6$ may be an ideal candidate for studying frustrated magnetism.

The recently discovered van der Waals magnetic semiconductor $\mathrm{Cr}{\mathrm{I}}_2$ shows promise for spintronic applications. Its electronic and magnetic properties are known to be strongly influenced by electronic correlations. In this work, we employ density functional theory calculations where electronic correlations in $\mathrm{Cr}{\mathrm{I}}_2$ are considered within an on-site Coulomb interaction, $U$, with $U$ being determined using the perturbative approach based on the linear-response method. We show that the accuracy of an on-site Coulomb interaction is essential for predicting the noncentrosymmetric orthorhombic ground state of $\mathrm{Cr}{\mathrm{I}}_2$, which allows the existence of ferroelectricity and nonzero Dzyaloshinskii-Moriya interaction (DMI). Our calculation shows that the ground state of bulk $\mathrm{Cr}{\mathrm{I}}_2$ has electric polarization of $0.15\mu \mathrm{C}/\mathrm{c}{\mathrm{m}}^{-2}$ pointing along the $z$-axis and the small DMI energy that changes sign with the ferroelectric polarization switching. The DMI and polarization are enhanced to 0.28 meV/formula-unit and $0.63\mu \mathrm{C}/\mathrm{c}{\mathrm{m}}^{-2}$ when Pt intercalates bilayers of $\mathrm{Cr}{\mathrm{I}}_2$, due to its large spin-orbit-coupling strength and large off-center displacement. Such an enhanced DMI leads to the Néel skyrmions, whose handedness is controlled by ferroelectric polarization. Our work contributes to the creation and manipulation of bits in skyrmions-based memory devices.

We calculate the values of observables in chiral eigenstates of the XX quantum spin chain that were introduced in previous work and compare the form of the result with the respective expressions obtained in the more familiar eigenbasis of states with fixed magnetization in the $z$ direction. We carry out the diagonalization of the XY spin chain in the chiral basis. We calculate the norm of the chiral XY eigenstates, and the values of the one-point functions and some neighbor two-point correlation functions. We interpret the spectrum and the particle content of the XY chain in terms of scattering states of an even number of kink and antikink excitations that are created over a reduced Brillouin zone.

We present a protocol for automated fitting of magnetic moment tensor potential explicitly including magnetic moments in its functional form. For the fitting of this potential we use energies, forces, stresses, and magnetic forces (negative derivatives of energies with respect to magnetic moments) of configurations selected with an active learning algorithm. These selected configurations are computed using constrained density functional theory, which enables calculating energies and their derivatives for both equilibrium and nonequilibrium (excited) magnetic states. We test our protocol on the system of B1-CrN and demonstrate that the automatically trained magnetic moment tensor potential reproduces mechanical, dynamical, and thermal properties of B1-CrN in the paramagnetic state with respect to density functional theory and experiments.

${\mathrm{Ho}}_3{\mathrm{ScO}}_6$ harbors a frustrated maple leaf lattice (MLL). It crystalizes in the ${\mathrm{Mg}}_3{\mathrm{TeO}}_6$-type structure and has a centrosymmetric trigonal space group ($R\overline{3}$). This system contains stacked layers of magnetic rings along the $c$ axis consisting of six magnetic ${\mathrm{Ho}}^{3+}$ ions forming Ho hexagons, which are connected into a two-dimensional network by equilateral and isosceles triangles to form a rare example of a MLL. Long-range magnetic order is reached below $T_N=4.1\mathrm{K}$ with a ${120}^{\circ }$ spin arrangement on the equilateral triangles, resulting in a positive vector chirality ground state configuration.

The polarization transition inside ferroelectric materials can significantly affect their electronic properties, leading to wide applications in the field of nanoelectronics. However, the effect of polarization direction on thermal transport is still not well understood. In this paper, we report the effective regulation of thermal transport behavior in ferroelectric $\alpha \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$ by adjusting its polarization phase. In the intrinsic ferroelectric phase $\alpha \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$ (${\mathrm{T}}_1$), because of the aligned polarization direction and structural symmetry, numerous degenerate phonon branches appear in the phonon spectrum. In this case, scattering channels between coupled phonons are restricted by energy conservation requirements during the phonon scattering process. However, most of these degenerate phonon branches become significantly decoupled when the ferroelectric ${\mathrm{T}}_1$ phase transitions to a new stable ferrielectric ${\mathrm{T}}_2$ phase. As a result, a significant number of scattering channels open up, leading to a substantial increase in scattering phase space in the ${\mathrm{T}}_2$ structure. This enlarged scattering phase space can lead to stronger phonon anharmonic scattering and significantly suppress thermal transport. For instance, the room temperature thermal conductivity of the ${\mathrm{T}}_2$ phase along the interlayer direction decreases by 64% compared to the ${\mathrm{T}}_1$ phase. Meanwhile, phonon coherence exists in both the ${\mathrm{T}}_1$ and ${\mathrm{T}}_2$ structures, where wave-like thermal transport plays a more significant role in the ${\mathrm{T}}_2$ case, particularly in the interlayer direction. The insights provided by this study offers an approach for the efficient regulation of thermal transport behavior in advanced functional materials.

Recent work has shown that the honeycomb lattice spin-$\frac{1}{2}{J}_1\text{−}{J}_3$ XY model, with nearest-neighbor ferromagnetic exchange $J_1$ and frustration induced by third-neighbor antiferromagnetic exchange $J_3$, may be relevant to a wide range of cobaltate materials. We explore a variational Monte Carlo (VMC) study of Gutzwiller projected wave functions for this model and show that an easy-plane Dirac spin liquid (DSL) is a viable “parent” state for the competing magnetic orders observed in these materials, including ferromagnetic, zigzag, spiral, and double zigzag orders at intermediate frustration, and show that such broken-symmetry states can be easily polarized by a weak in-plane magnetic field consistent with experiments. We formulate a modified parton theory for such frustrated spin models, and explore the potential instabilities of the DSL due to residual parton interactions within a random phase approximation (RPA), both at zero magnetic field and in a nonzero in-plane field. The broken-symmetry states which emerge in the vicinity of this Dirac spin liquid include ferromagnetic, zigzag, and incommensurate spiral orders, with a phase diagram which is consistent with VMC and density matrix renormalization group studies. We calculate the dynamical spin response of the easy-plane DSL, including RPA corrections, near the boundary of the ordered states, and present results for THz spectroscopy and inelastic neutron scattering, at zero field as well as in an in-plane magnetic field, and discuss experimental implications.

The Nernst effect of the magnon orbital moment is theoretically investigated in a honeycomb ferromagnet, whose Hamiltonian contains the Heisenberg exchange, the Dzyaloshinskii-Moriya, the Kitaev, and the Zeeman interactions. More specifically, we obtain the magnon band structure, the Berry curvature, the magnon orbital moment Berry curvature, and the magnon orbital moment Nernst conductivity (MOMNC) for the Hamiltonian within the linear spin-wave theory in the polarized phase. We found the magnon orbital moment Berry curvature is largely independent of the sign of the Chern number of the band. For an experimental proposal, we estimate MOMNC of ${\mathrm{CrI}}_3$ for the Heisenberg-Kitaev-$\mathrm{\Gamma }$-Zeeman model and Heisenberg-Dzyaloshinskii-Moriya-Zeeman model for a perpendicular external magnetic field. We found that certain Kitaev materials provide us with a broad tunability of the MOMNC through a magnetic field. We envision that our findings lead to further investigations of the novel transport properties of the magnon orbital moment.

The half-chain entanglement entropy (EE) of the one-dimensional $XX$ (isotropic $XY$) chain and quantum Ising chain (QIC) at the critical point are calculated numerically for large lattices. The periodic, free-free, fixed-fixed ($++$) and ($+-$), and fixed-free boundary conditions (BCs) are studied. The models are transformed into a fermion system with a Jordan-Wigner transformation. The correlation functions of these fermions are obtained numerically. With the correlation functions, the entanglement entropy is obtained. The numerical calculation is performed with quadruple precision. The numerical results agree with the exact relationship with an accuracy of ${10}^{-28}$ between the EEs of the $XX$ chain and QICs: (1) the EE of the $XX$ chain with periodic BCs is the sum of two QICs with periodic BCs; (2) the EE of the $XX$ chain with free-free BCs is the sum of two QICs with free-free BCs; (3) the EE of the $XX$ chain with fixed-free BCs is the sum of the EE of a QIC with fixed-free BCs and that with free-free BCs; (4) the EE of the $XX$ chain with fixed-fixed ($++$) BCs is the sum of the EE of a QIC with fixed-fixed ($++$) BCs and that with free-free BCs; and (5) the EE of the $XX$ chain with fixed-fixed ($+-$) BCs is the sum of the EE of a QIC with fixed-fixed ($++$) BCs and that of the first excited state of a QIC with free-free BCs. We fit the half-chain EE with finite-size scaling expansion of terms $L^{-n}$ and $L^{-n}lnL$, where $L$ is the length of the spin chain. We find that the fitted parameters for the leading term $lnL$ and the constant term are consistent with conformal field theory and that the exact solutions are highly accurate. The fitting accuracy is so high that the fitted central charge of the Ising model is $0.5\pm 1\times {10}^{-26}$ for the periodic boundary condition. From the higher-order corrections in the fitted expansion, we find that there exist $L^{-4}lnL$ and higher-order corrections for the fixed-fixed ($+-$) boundary conditions, whereas there exist $L^{-3}lnL$ and higher-order corrections for the fixed-free boundary conditions. These types of corrections mean corrections of the central charge.

We investigated the pressure effects of superconductivity on thin films of Sn. The elemental superconductor Sn with a body-centered-tetragonal structure, $\beta$-Sn, exhibits superconductivity below the superconducting transition temperature ($T_{\mathrm{c}}=3.72$ K) at ambient pressure. $T_{\mathrm{c}}$ of Sn increases with lowering dimension such as in thin-film and nanowire growth, or by high-pressure application. For thin films, $T_{\mathrm{c}}$ exhibits a slight increase up to approximately 4 K compared to the bulk value, attributable to the crystalline size and lattice disorder. By applying pressure on a bulk Sn, $T_{\mathrm{c}}$ initially decreases from 3.72 K as the pressure increases. Further increasing pressure up to 10 GPa, $T_{\mathrm{c}}$ increases to 5.3 K with the structural transformation. However, the combination of these effects on thin films of Sn, namely, thin-film growth and pressure effects, remains underexplored. In this paper, we combined film-growth and pressure-application techniques to further increase $T_{\mathrm{c}}$ using a diamond anvil cell with boron-doped diamond electrodes. The drop of electrical resistance suggesting the onset of $T_{\mathrm{c}}$ on the thin film reached above 6 K in the $\gamma$-Sn phase. Further, the upper critical magnetic field was drastically enhanced. Atomic force microscopy suggests that the refinement of the grain size of the thin film under nonhydrostatic pressure conditions contributes to stabilizing the higher $T_{\mathrm{c}}$ of $\gamma$-Sn.