The search of quantum anomalous Hall (QAH) effect and other Hall effects is promising for developing high-performance electronic and spintronic devices. By employing the first-principles calculations, we find the existence of QAH effect and valley Hall effect in two-dimensional (2D) ${\mathrm{Ti}}_3{\mathrm{STe}}_4$ monolayer. The ${\mathrm{Ti}}_3{\mathrm{STe}}_4$ monolayer is a robust Weyl half metal with the Weyl point protected by vertical mirror symmetry $M_v$. By considering the spin orbital coupling (SOC) effect, the monolayer is transformed to be a QAH insulator with a sizable band gap. More remarkably, the valley-polarized quantum anomalous Hall (VP-QAH) state is realized in ${\mathrm{Ti}}_3{\mathrm{STe}}_4$/${\mathrm{Sc}}_2{\mathrm{CO}}_2$ heterostructure due to the broken combined mirror symmetry $\left(M_v\right)$ and time reversal symmetry (T). Through the development of a spinless three-band tight-binding model based on first-principles calculations, we reproduce density functional theory results and provide insight into the emergence of the VP-QAH state. Our findings greatly enrich the research on QAH and VP-QAH physics and their potential application on spintronic devices.

We study quantum entanglement in a system comprising two quantum dots interconnected through the short topological superconducting nanowire, which hosts overlapping boundary Majorana modes. Inspecting the fermionic negativity, we analyze the variation of entanglement against the position of the energy levels of quantum dots and their hybridization with the topological superconducting nanowire. In the absence of electron correlations, the optimal entanglement occurs when the energy levels coincide with the zero-energy Majorana modes, whereas upon increasing the hybridizations, the entanglement is gradually suppressed. Such monotonous behavior is no longer valid when the quantum dot levels are detuned from the zero-energy. Under these circumstances, the quantum dots become maximally entangled for a certain optimal hybridization. Moreover, we study the thermal concurrence to explore the entanglement properties at finite temperatures. We also compute the quantum mutual information and propose recipes for robust finite-temperature entanglement transmission via Majorana modes.

Motivated by the recent experimental findings on the orbital ordering of cuprate superconductors (SC), we investigated the multiorbital Cu impurity including local exchange and Coulomb interactions embedded in the O lattice by incorporating the $3d^8$ multiplet structure coupled to a full O-$2p$ band. Instead of providing physical mechanism of this spontaneous symmetry breaking, we systematically investigate the impact of artificial anisotropy of various parameters to reveal rich phenomena in terms of the ground-state (GS) weight asymmetry between the $\widehat{x}$ and $\widehat{y}$ directions. The numerical evidence demonstrates that the GS weight of the Zhang-Rice singlet (ZRS) can be affected by the asymmetry of these parameters to distinct extent. Although the experimentally motivated asymmetric charge transfer energy only induces a tiny weight difference, the asymmetric $d\text{−}p$ hybridization can result in considerable asymmetry of the GS weight, which also intriguingly shows that the critical charge transfer energy separating the ${}^{1}A_1$ singlet and ${}^{3}B_1$ triplet GS is independent of the intermediate asymmetry ratio regime. More importantly, the nearest-neighbor (NN) $V_{pd}$ has much stronger impact than the local $U_{pp}$, which stems from the nature of ZRS consisting of nearest-neighbor two holes. Our systematic exploration provides valuable knowledge on the role of the artificial symmetry breaking on the two-hole GS nature and serves as the starting point of more sophisticated many-body simulations to uncover more interesting physics of the multiorbital Cu lattice model within the symmetry breaking setup.

In this paper we study the three-dimensional (3D) gauge theory of two tensor gauge fields: $a_{\mu \nu }\left(x\right)$, which we take symmetric, and $B_{\mu \nu }\left(x\right)$, with no symmetry on its indices. The corresponding invariant action is a higher-rank BF-like model, which is first considered from a purely field theoretical point of view, and the propagators with their poles and the degrees of freedom are studied. Once matter is introduced, a fracton behavior naturally emerges. We show that our theory can be mapped to the low-energy effective field theory describing the Rank-2 toric code (R2TC). This relation between our covariant BF-like theory and the R2TC is a higher-rank generalization of the equivalence between the ordinary 3D BF theory and Kitaev's toric code. In the last part of the paper we analyze the case in which the field $B_{\mu \nu }\left(x\right)$ is a symmetric tensor. It turns out that the obtained BF-like action can be cast into the sum of two rank-2 Chern-Simons actions, thus generalizing the ordinary Abelian case. Therefore, this represents a higher-rank generalization of the ordinary 3D BF theory, which well describes the low-energy physics of quantum spin Hall insulators in two spatial dimensions.

The photonic spin Hall effect (PSHE) plays a key role in the development of efficient spin-based selective devices. However, the quality factor (Q-factor), another core indicator for stronger light-matter interaction in spin-based optoelectronic devices, has rarely been considered for enhanced PSHE. In this paper, we demonstrate the enhancement mechanism of PSHE in a continuum bound state (BIC) metasurface with a high Q-factor. By utilizing the ultraweak angular dispersion of our specially designed three-tier architecture quasi-BIC (q-BIC) metasurface, the first-order partial derivative term of the Fresnel coefficient has been suppressed at a very low level. Coupled with a large Fresnel coefficient ratio and high Q-factor, the transverse shift of PSHE is greatly enhanced. In addition, by tuning the thickness of the substrate layer, the incident angle of maximum transverse shift can be flexibly manipulated. In this paper, we uncover the physical mechanism for enhancing PSHE in a BIC structure and offer a foundation for designing high-performance spin-based optoelectronic devices.

The long-awaited fractional quantum anomalous Hall (FQAH) effect recently has been observed in the twisted ${\mathrm{MoTe}}_2$ homobilayers, causing a great sensation. Here we theoretically investigate the moiré band structures of a closely related system, the alternating twisted multilayer ${\mathrm{MoTe}}_2$ (ATML-${\mathrm{MoTe}}_2$), where the adjacent layers have opposite twist angles. We illustrate that such ATML-${\mathrm{MoTe}}_2$ is a very unique moiré system, exhibiting multiple topological flat bands highly controllable by the layer number and twist angle, which is not only an ideal platform to simulate Hubbard model but also may host FQAH states. Specifically, an $N$-layer ATML-${\mathrm{MoTe}}_2$ ($N\ge 3$) always possesses $N-2$ topological flat bands near Fermi energy $E_f$, which has an odd-even dependent decomposition rule to understand the behaviors of the moiré flat bands. We predict three intriguing examples: (1) The AT3L-${\mathrm{MoTe}}_2$ ($N=3$) has one isolated moiré flat band, which corresponds to a triangular lattice Hubbard model, resembling the twisted transition metal dichalcogenides heterobilayers. (2) The AT4L-${\mathrm{MoTe}}_2$ ($N=4$) has two topological flat bands that are very similar to the twisted ${\mathrm{MoTe}}_2$ homobilayers, implying the possible existence of FQAH states. (3) When $N>4$, the giant density of states induced by the multiple moiré flat bands may induce exotic correlated states.

Phonon coherence elucidates the propagation and interaction of phonon quantum states within superlattice, unveiling the wavelike nature and collective behaviors of phonons. Taking ${\mathrm{MoSe}}_2/{\mathrm{WSe}}_2$ lateral heterostructures as a model system, we demonstrate that the intricate interplay between wavelike and particlelike phonons, previously observed in perfect superlattice only, also occurs in disordered superlattice. By employing molecular dynamics simulation based on a highly accurate and efficient machine-learned potential constructed herein, we observe a nonmonotonic dependence of the lattice thermal conductivity on the interface density in both perfect and disordered superlattice, with a global minimum occurring at relatively higher interface density for disordered superlattice. The counterintuitive phonon coherence contribution can be characterized by the lagged self-similarity of the structural sequences in the disordered superlattice. Our findings extend the realm of coherent phonon transport from perfect superlattice to more general structures, which offers more flexibility in tuning thermal transport in superlattices.

A recent experiment reports the creation of goldene, which is two-dimensional gold with a hexagonal structure. By rolling up the goldene, gold nanotubes (GNTs) should exist, but their structural and electronic properties are not well understood. Based on first-principles calculations, we demonstrate a breakdown of the inverse square law, wherein the strain energy stored in a GNT decreases with the inverse square of the GNT radius. This is due to the enhanced strain energy in specific GNTs. The specific chiralities are identified by imposing the Bloch and geometric boundary conditions to the electronic structure of goldene having a hexagonal shape of the Fermi surface. We also confirm that the electronic states on the Fermi surface exhibit an in-plane character. These factors result in an increase in the strain energy.

The transition-metal dichalcogenides featuring Ising spin-orbit coupling in so-called Ising superconductors offer a unique system to study the interplay of singlet and triplet superconductivity. The presence of high critical fields, spectral properties such as the mirage gap, and field-tunable charge and spin currents in Ising superconductor Josephson junctions are some of the important features. In this Letter, we study an Ising superconductor Josephson junction with a transparent interface and show that Andreev bound states are spin split due to a relative misorientation of in-plane fields in the superconducting contacts. Correspondingly, supercurrent-phase relations display a strongly nonsinusoidal behavior. Introducing additional spin-polarized channels with low transmission results in a nonreciprocal current-phase relation with a diode effect that can be tuned by the in-plane exchange fields. The diode efficiency reaches high values of the order of 40% and is not sensitive to disorder in the junction. Such structures can be realized in van der Waals heterostructures of two-dimensional superconductors and magnets.

Like electrons, Cooper pairs can carry a monopole charge if the pairing electrons come from two or more Fermi surfaces with different Chern numbers. In such an instance, a superconductor is necessarily nodal due to an inherent topological pairing obstruction. In this work, we show that a similar obstruction is also possible when there is only one Fermi surface involved in the pairing process. By developing a Chern-vorticity theorem, we have identified a class of Fermi surfaces with a quantized dipolar Berry flux pattern, where all intra-Fermi-surface Cooper pairings are “dipole obstructed” and nodal. As a real-world application, we find that the dipole obstruction plays a crucial role in stabilizing the superconducting nodal structure for $j=\frac{3}{2}$ half-Heusler compounds.

Dissipation usually has negative effects on magnon-photon entanglement and thus is engineered to a low level in many works. In this work, we propose a theoretical scheme to generate steady-state magnon-photon entanglement by using the dissipatively coupled magnon and photon in a squeezed vacuum reservoir. It is found that the reservoir-mediated magnon-photon coupling and the squeezing nature of reservoir result in the entanglement. As the coupling strength increases or intrinsic dissipation decreases, the magnon-photon correlation and entanglement can be enhanced. As the squeezing amplitude $r$ of reservoir increases, the logarithmic negativity, which is the measure of entanglement, presents a maximum at an optimal value of $r$. This reflects the competition between the enhancement of magnon-photon correlation which favors the entanglement, and the increase in the input noise which destroys the entanglement. We also propose a device geometry which could be realized with existing technology of cavity magnon polariton and superconducting Josephson parametric amplifiers. Our theoretical methods and results may be useful for future theoretical studies of magnon-photon or magnon-magnon entanglement and experimental studies of magnon-based quantum communication and manipulations.

Fictitious magnetic fields can be introduced in quantum magnets by strain engineering and the Aharonov-Casher effect. Here, we study impacts of a uniform fictitious magnetic field and corresponding Landau quantization on the Néel order in the $S=\frac{1}{2}$ Heisenberg model on the square lattice as a prototypical system of quantum magnets. We first analyze the system by using the spin-wave approximation. It is found that the staggered magnetization is enhanced by the fictitious magnetic field and it shows a simple scaling behavior with respect to the magnetic length, in contrast with a naive expectation based on the Dzyaloshinskii-Moriya interaction. We also perform density-matrix-renormalization-group calculations to fully consider quantum effects and obtain quantitatively more accurate results. The enhancement is found to be anomalously strong, and it shows a nontrivial scaling behavior or a fluctuation induced discontinuity. These results are beyond the well-known understanding of correlated systems under magnetic fields called the magnetic catalysis.

The interplay of magnetism and superconductivity is of long-standing interest in condensed matter physics. Layered and 2D superconductors provide a particular opportunity for studying this due to the fact that layer substitutions and adlayers can be used to combine superconducting and magnetic materials. Here we investigate the coupling between fcc Fe and ${\text{SrTiO}}_3$ supported FeSe monolayers. We find that Fe on FeSe monolayers energetically prefers a magnetic fcc structure. The interaction between Fe overlayers and the FeSe monolayer is relatively strong, and in particular it can cause both changes in the FeSe orbital nature near the Fermi level and alterations in the magnetic structure. Notably, we find a change from $t_{2g}$ to $e_g$ orbital character near the Fermi level with Fe overlayers, with the $e_g$ orbital slightly larger with thick Fe overlayers. We discuss the details of the changes and their origin.

We consider longitudinal electronic transport in a graphene monolayer with an external in-plane magnetic field parallel to the electric field and in the presence of extrinsic spatially fluctuating spin-orbit Rashba interaction. Our main focus is on the longitudinal magnetoresistance. We show that for a spin-orbit correlation length $\xi$ between ${10}^{-6}$ and ${10}^{-5}$ cm, scattering processes on the Rashba spin-orbit fluctuations lead to a negative magnetoresistance. For smaller correlation lengths, $\xi <{10}^{-6}$ cm, we find a small and positive magnetoresistance. The description is based on an effective model of a graphene Hamiltonian that is valid for low-energy states around the Dirac points. In turn, to derive the electron scattering rate and the longitudinal conductivity and magnetoresistivity, we employ the linear response theory and Green's function formalism.

Searching of materials, where a long-range magnetic order is suppressed by quantum fluctuations and a quantum spin liquid state realizes, is one of the central problems in the modern condensed matter physics. A possible candidate for such a state on the breathing Kagome lattice ${\mathrm{LiZn}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$ is scrutinized by hard x-ray photoemission spectroscopy (HAXPES), cluster dynamical mean-field theory (cDMFT), and exact diagonalization of an extended Hubbard model. The Mo $3d$ core level HAXPES peaks of ${\mathrm{LiZn}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$ are accompanied by shoulders on their lower energy side which are absent in ${\mathrm{Zn}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$. The shoulder peaks observed only in ${\mathrm{LiZn}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$ indicate ${\mathrm{Mo}}^{3+}$ and ${\mathrm{Mo}}^{4+}$ charge fluctuations. The cDMFT calculations not only describe experimental valence-band HAXPES spectra demonstrating importance of the correlation effects, but also feature nonlocal spin fluctuations. Exact diagonalization taking into account intertrimer Coulomb repulsion demonstrates long-range charge fluctuations consistent with HAXPES results.

The different modes of the spin dynamics in ferrimagnetic magnetite iron oxide nanoparticles (${\mathrm{Fe}}_3{\mathrm{O}}_4$) have been addressed by µeV neutron spectroscopy for particles with a diameter of 75 ± 18 Å. In an approach building on intensity considerations over a wide range of wave vectors $Q$ in combination with diffusion dynamics, we identify three magnetic modes prevailing in distinct $Q$ regimes up to 1.7 ${\AA }^{-1}$: (i) Evaluating the structure factor of quasielastic magnetic intensity enables to identify uniquely longitudinal superparamagnetic spin fluctuations in the small $Q$ regime $<0.5{\text{Å}}^{-1}$, (ii) individual spin relaxation with quasielastic intensity albeit of low intensity is present in two $Q$ ranges of 0.5 ${\text{Å}}^{-1}<Q<1.0{\text{Å}}^{-1}$ and 1.5 ${\text{Å}}^{-1}<Q<1.7{\text{Å}}^{-1}$, and (iii) a surprisingly low-energy inelastic spin excitation of 23.2 µeV in magnetite IONPs is found at 150 K in the magnetic Bragg region between 1.1 ${\AA }^{-1}<Q<1.4{\text{Å}}^{-1}$. Its temperature dependence suggests a collapse of the coherent transverse magnetic fluctuations and a transition into a generalized diffusive mode at about 500 K.

Discovering and categorizing quantum orders in mixed many-body systems are currently one of the most important problems. Specific types of decoherence applied to typical quantum many-body states can induce a novel kind of mixed state accompanying characteristic symmetry orders, which has no counterparts in pure many-body states. We study phenomena generated by the interplay between two types of decoherence applied to the one-dimensional transverse field Ising model (TFIM). We show that in the doubled Hilbert space formalism, the decoherence can be described by a filtering operation applied to matrix product states (MPS) defined in the doubled Hilbert system. The filtering operation induces specific deformation of the MPS, which approximates the ground state of a certain parent Hamiltonian in the doubled Hilbert space. In the present case, such a parent Hamiltonian is the quantum Ashkin-Teller model, having a rich phase diagram with critical lines and quantum phase transitions. By investigating the deformed MPS, we find various types of mixed states emergent from the ground states of the TFIM and clarify phase transitions between them. In that study, strong and weak $Z_2$ symmetries play an important role, for which we introduce efficient order parameters, such as Rényi-2 correlators, entanglement entropy, etc., in the doubled Hilbert space.

The effect of electron irradiation on two-dimensional (2D) materials is an important topic, both for the correct interpretation of electron microscopy experiments and for possible applications in electron lithography. After the importance of including inelastic scattering damage in theoretical models describing beam damage and the lack of oxygen sensitivity under electron irradiation in 2D ${\mathrm{MoS}}_2$ were recently shown, the role of temperature has remained unexplored on a quantitative level. Here we show the effect of temperature on the creation of individual defects and the effect of temperature on defect dynamics. Based on the measured displacement cross section of sulfur atoms in ${\mathrm{MoS}}_2$ by atomic resolution scanning transmission electron microscopy, we find an increased probability for defect creation for temperatures up to $150{}^{\circ }\mathrm{C}$, in accordance with theoretical predictions. However, higher temperatures lead to a decrease of the observed cross sections. Despite this apparent decrease, we find that the elevated temperature does not mitigate the creation of defects as this observation would suggest, but rather hides the created damage due to rapid thermal diffusion of the created vacancies before their detection, leading to the formation of vacancy lines and pores outside the measurement's field of view. Using the experimental data in combination with previously reported theoretical models for the displacement cross section, we estimate the migration energy barrier of sulfur vacancies in ${\mathrm{MoS}}_2$ to be $0.26\pm 0.13\mathrm{eV}$. These results mark another step towards the complete understanding of electron beam damage in ${\mathrm{MoS}}_2$.