We theoretically investigate magnons on the $\alpha \text{−}{T}_3$ lattice. Atomistic spin dynamics simulations show that next-nearest neighbor hopping and easy-axis anisotropy stabilize ferromagnetic order in the presence of Dzyaloshinskii-Moriya interaction. We identify one topologically trivial magnon insulator phase and three magnon Chern insulator phases. The topologically trivial magnon insulator phase exhibits a small but nonzero magnon thermal Hall conductivity, while in the magnon Chern insulator phases the Chern number of the lowest magnon band dominates the magnon thermal Hall conductivity. The sign of the magnon thermal Hall conductivity does not change at the topological phase boundaries, but distinct changes are observed in the magnitude.

The recent suggestion of valence-skipping phenomenon driving a two-gap superconductivity in $Ag$-doped SnSe by Kataria et al. [Phys. Rev. B 107, 174517 (2023)] has brought to the fore a long-standing issue once again. The absence of crystallographically inequivalent Sn sites corroborated by electronic properties of ${\mathrm{AgSnSe}}_2$, calculated using first-principles density functional theory, however, does not appear to provide strong support in favor of valence skipping in ${\mathrm{AgSnSe}}_2$. Interestingly, the signature of avoided band crossings (with the inclusion of spin-orbit coupling) and nonzero mirror Chern number ($n_{\mathcal{M}}$) suggest a nontrivial topology. The presence of mirror symmetry-protected surface states along the mirror planes indicates that ${\mathrm{AgSnSe}}_2$ could be a potential candidate for topological crystalline metals (TCMs), with a transition from a topological crystalline insulator phase to a TCM phase under Ag doping. Moreover, using the Migdal-Eliashberg theory of electron-phonon coupling and anisotropic superconductivity in ${\mathrm{AgSnSe}}_2$, we predict a single superconducting gap and a critical temperature $T_c\approx 7\mathrm{K}$, consistent with the experimental value. The interplay of topology and superconductivity in this three-dimensional material appears quite intriguing and may provide insights into the nature of superconductivity in systems with nontrivial topology.

Recently, a flurry of works have found strong competition between charge density wave (CDW) and superconductivity (SC) in the doped Hubbard and $t\text{−}J$ models on the square lattice. Interestingly, some recent results suggest that the electron-phonon coupling may suppress CDW order and enhance SC. In this work, we consider the square-lattice Hubbard model with the Holstein or Su-Schrieffer-Heeger electron-phonon coupling at the large-$U$ and antiadiabatic (infinite phonon frequency) limits, which gives an effective $t\text{−}J$ model with either a density attractive interaction $V$ or a $J_P$ term that contributes a larger spin exchange and a density repulsive interaction. To explore how these effective couplings may tune the competition between CDW and SC, we implement the density matrix renormalization group simulations on the $t\text{−}{t}^{\prime }\text{−}J$ model with $V$ or $J_P$ coupling. We focus on the six-leg cylinder system with the next-nearest-neighbor hopping $t^{\prime }$, which hosts partially filled stripe and $d$-wave SC in phase diagram. By tuning $t^{\prime }/t>0$ and $V$ or $J_P$, we establish two quantum phase diagrams at $\frac{1}{12}$ doping ratio. In the SC phases, the increased $V$ or $J_P$ coupling can enhance the quasi-long-range SC order, consistent with some previous findings. Nonetheless, no SC emerges when the partially filled stripe phase disappears with increased $V$ or $J_P$. Instead, the system has a transition to either a phase-separation-like regime or a filled stripe phase. On the other hand, with increased $t^{\prime }/t$, not only the partially filled stripe but the phase separation and filled stripe can also be tuned to SC phase. Our results suggest that although $V$ and $J_P$ couplings may strengthen hole binding, the hole dynamics controlled by $t^{\prime }/t$ appears to play a more crucial role for obtaining a SC in the $t\text{−}J$ model.

Spin band splitting in noncentrosymmetric systems attracts considerable attention as a key for next-generation spintronics. Since spin textures in momentum space are characterized by the lattice symmetry and spin-orbit interaction inherent to constituent atoms, it is challenging to control them with external fields whose energy scales are quite small compared to the Fermi energy. In this study, we report that in half-Heusler compounds $R\mathrm{AuSn}$ ($R=\mathrm{Ho}$,Er,Tm,Lu), spin textures arising from an antisymmetric spin-orbit interaction are manipulated by a magnetic field via exchange interactions, accompanied by a several orders of magnitude change of resistivity. We find that the lattice constant shrinks by approximately 0.9% upon the substitution of $R$ ions from Ho to Lu, leading to the marked modification of the electronic states from a semiconductor with an indirect gap of 23 meV to a semimetal with high mobility carriers of $14000{\mathrm{cm}}^2/\mathrm{V}\mathrm{s}$. Despite such a large difference in the transport properties at zero field, the resistivities of all three magnetic compounds exhibit a universal magnetization dependence and reach minimal residual resistivity of less than $1\mu \mathrm{\Omega }\mathrm{cm}$ at the saturated magnetization, implying the emergence of another high-mobility semimetal in ferromagnetic-like states. The analysis of the quantum oscillation reveals that the large spin-orbit-induced band splitting of $2.3\mathrm{meV}$ occurs for nonmagnetic LuAuSn, while the energy of the band exchange splitting exceeds 200 meV for magnetic HoAuSn with fully polarized moments. Combined with first-principles calculations, we find that such a large exchange splitting gives rise to Weyl points and thereby modulates the spin-momentum locking, to which the observed colossal magnetoresistance can be attributed. These findings demonstrate that this family of materials hosts a high tunability of spin textures as well as electronic states by external fields and chemical pressures, opening an important arena for topological quantum materials.

Structure and electronic properties of self-trapped holes were studied in both crystalline and amorphous ${\mathrm{Ga}}_2{\mathrm{O}}_3$ using density functional theory (DFT) and the nonlocal PBE0-TC-LRC density functional. Amorphous (a) ${\mathrm{Ga}}_2{\mathrm{O}}_3$ structures were generated using classical molecular dynamics and the melt-quench technique and further optimized using DFT. They exhibit an average density of $4.84\mathrm{g}/{\mathrm{cm}}^3$ and band gap around 4.3 eV. Calculations predict deep hole trapping in crystalline and amorphous phases with the hole-trapping energies in the amorphous structures being deeper than those found in the crystalline structure. In $\mathrm{a}\text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$, trapped holes are localized around low-coordinated oxygen atoms (two or three coordinated). We predict the formation of stable hole bipolarons in both the crystalline and amorphous phases facilitated by the formation of O–O bonds with binding energies about 0.2 eV.

In recent years, the interplay between non-Hermiticity and band topology has been expected to uncover numerous physical phenomena. However, the majority of research has focused on periodic crystalline structures, with comparatively fewer studies exploring quasicrystalline systems. In this paper, we delve into the influence of asymmetric hopping on topological insulators, specifically focusing on quantum spin Hall insulators and higher-order topological insulators in an octagonal Ammann-Beenker quasicrystalline lattice. We demonstrate that asymmetric hopping can significantly alter the distribution of edge states, leading to a uniform distribution across all boundaries or localizing them at a single edge, depending on the symmetry adjustments. Furthermore, we explore the robustness of higher-order topological corner states under perturbations, showing that these states can maintain their distribution even in the presence of non-Hermiticity. Our findings not only expand the current understanding of topological states in quasicrystals under non-Hermitian conditions but also provide valuable theoretical guidance for manipulating corner state distributions in non-Hermitian quasicrystalline higher-order topological insulators.

We theoretically investigate the trARPES (time-resolved ARPES) spectrum and optical Hall conductivity in periodically driven twisted bilayer graphene, considering both steady-state and “projected” occupations of the Floquet state. In periodically driven prethermalized systems, steady-state occupation of Floquet states is predicted to occur when coupled to a bath, while these states have projected occupation instantaneously after the driving starts. We study how these two regimes can give markedly different responses in optical transport properties. In particular, our results show that steady-state occupation leads to near-quantized optical Hall conductivity for a range of driving parameters in twisted bilayer graphene, whereas projected occupation leads to nonquantized values. We discuss the experimental feasibility of probing such nonequilibrium states in twisted bilayer graphene.

Interfaces between glass and metals are of paramount importance from many technological aspects. However, the information on surface energies of glass and their interfacial energies with metals is surprisingly absent in the literature. Here, we propose a protocol based on first-principles calculations and ab initio molecular dynamics simulations assisted by machine-learning force fields to address this problem. We evaluate the surface energy of silica glass and its interfacial energy with three metals (Cu, Ag, and Au). The surface models of glass are generated by using a potential wall approach and based on these surface models a sufficient number of interface models are constructed. Then, the surface energy of silica glass and the interfacial energies are evaluated by a statistical approach. Converged surface energy of 49 meV/Å${}^2$ is obtained for silica glass. Its interfacial energies with the (001) surfaces of Cu, Ag, and Au are calculated to be 104, 76, and 86 meV/Å${}^2$, respectively. The lowest interfacial energy between Ag and glass is consistent with experiments that show good wettability of glass on Ag surface.

A fundamental challenge in pursuing topological states in twisted homobilayer transition metal dichalcogenides is the relative energies between the valence band extrema at the topologically trivial $\mathrm{\Gamma }$ and nontrivial $K/K^{\prime }$ valleys. We employ many-body perturbation theory within the $\mathit{GW}$ approximation to investigate the energy difference of the valence band extrema in homobilayer ${\mathrm{WSe}}_2$ and ${\mathrm{MoTe}}_2$, the two most promising candidate platforms hosting various quantum phases. In contrast to the results obtained from density functional theory, the $\mathit{GW}$ calculation predicts quasiparticle energies of the $K/K^{\prime }$ valley above those of the $\mathrm{\Gamma }$ valley for all high-symmetry stackings. We further develop a “fractional folding” technique, allowing for the inclusion of substrate and encapsulating dielectric screening effects in $\mathit{GW}$ simulations. We find that while environmental dielectric screening from hexagonal boron nitride reduces the energy difference between the $K/K^{\prime }$ and $\mathrm{\Gamma }$ valley extrema, the valence band maximum remains situated at the topologically nontrivial $K/K^{\prime }$ valley. Finally, many-body effects enhance the depth of the moiré potential, leading to a shift of the “magic angle,” compared to the result from density functional theory. Our study offers quasiparticle energy landscapes to guide the search for twisted homobilayers of topological interest.

Low-dimensional multiferroic compounds are promising candidate materials for advanced multistate information devices, while most known multiferroics do not show macroscopic magnetic and ferroelectric orders at room temperature, becoming a serious barrier for practical applications. Based on the first-principles density-functional theory, we propose a two-dimensional ${\mathrm{TiCr}}_2{\mathrm{O}}_4$ semiconductor with coexisting ferroelectricity and room-temperature ferromagnetism. The ${\mathrm{TiCr}}_2{\mathrm{O}}_4$ monolayer presents ferromagnetic coupling, out-of-plane magnetic anisotropy, spontaneous perpendicular polarization of up to $0.12\mathrm{C}/{\mathrm{m}}^2$, and desired vertical piezoelectricity. Remarkably, the conductivity can be improved with robust out-of-plane magnetic anisotropy and ferromagnetism above room temperature in carrier-doped ${\mathrm{TiCr}}_2{\mathrm{O}}_4$ monolayer. Our work shows that the ${\mathrm{TiCr}}_2{\mathrm{O}}_4$ monolayer is a promising candidate for low-dimensional nonvolatile spintronic field-effect transistors.

Dense arrays of semiconductor quantum dots are currently employed in highly efficient quantum dot lasers for data communications and other applications. Traditionally, the electronic properties of such quantum nanostructures have been treated as isolated objects, with the degree of hybridization between neighboring quantum dots and the wetting layer left unexplored. Here, we use atom probe tomography and transmission electron microscopy to uncover the three-dimensional (3D) composition profile of a high-density ensemble of epitaxial InAs/GaAs quantum dots. The subnanometer compositional data are used to construct the 3D local band edge and simulate the electronic eigenstates within the dense quantum dot ensemble using the finite element method. This in situ electronic simulation reveals a high degree of hybridization between neighboring quantum dots and the wetting layer, in stark contrast to the usual picture of isolated quantum nanostructures. The simulated transition energies are compared with low-temperature photoluminescence. This work has important applications for quantum dot laser design and paves the way to engineering ensemble effects in quantum dot lasers and other quantum nanostructures.

Systems displaying topological quantum order feature robust characteristics that are very attractive to quantum computing schemes. Topological quantum field theories have proven to be powerful in capturing the quintessential attributes of systems displaying topological order including, in particular, their anyon excitations. Here, we investigate systems that lie outside this common purview, and present a rich class of models exhibiting topological orders with distance-dependent interactions between anyons. As we illustrate, in some instances, the gapped lowest-energy excitations are comprised of anyons that densely cover the entire system. This leads to behaviors not typically described by topological quantum field theories. We examine these models by performing exact dualities to systems displaying conventional (i.e., Landau) orders. Our approach enables a general method for mapping Landau-type theories to dual models with topological order, while preserving the same spatial dimension. The low-energy subspaces of our models can be made more resilient to thermal effects than those of surface codes.

As a recently identified Mott system, $\mathrm{PbCr}{\mathrm{O}}_3$ remains largely unexplored, especially for its band structure, leading to many contentious issues on its structural, electronic, and magnetic properties. Here we present a comprehensive study of two different $\mathrm{P}{{\mathrm{b}}_{1\text{−}}}_{\delta }\mathrm{Cr}{\mathrm{O}}_3$ (δ = 0 and 0.15) samples involving atomic deficiency prepared under pressure. By means of state-of-the-art diffraction techniques, the crystal structure of $\mathrm{PbCr}{\mathrm{O}}_3$ is definitively determined to adopt the pristine $\mathit{Pm}\overline{3}m$ symmetry, rather than other previously misassigned structures of M2-Pm$\overline{3}m$ and Pmnm. The two materials exhibit a similar charge-transfer-type insulating band structure, and the charge-transfer effect splits both Cr $2p$ and Pb $4f$ orbitals, rationalizing doublet splitting of the associated spectral lines. Nearly identical nominal cationic valence states of $\mathrm{C}{\mathrm{r}}^{4+}$ and $\mathrm{P}{\mathrm{b}}^{2+}$ are identified for this oxide system, hence calling into question the validity of recently proposed charge disproportionation mechanisms. In addition, $\mathrm{P}{\mathrm{b}}_{0.85}\mathrm{Cr}{\mathrm{O}}_3$ exhibits an anomalously higher Néel temperature of ∼240 K than that of $\mathrm{PbCr}{\mathrm{O}}_3$ (i.e., ∼200 K), likely due to the deficiency-induced enhancements of $\text{Cr3}d\text{–}\mathrm{O}2p$ orbital overlap and magnetic exchange. These findings provide much solid evidence to look into the fundamental properties of this important material system.

We report the magnetic and magnetotransport properties with electronic band-structure calculation of the Bi square net system ${\mathrm{PrAgBi}}_2$. The magnetization and heat capacity data confirm the presence of a crystalline electric field (CEF) effect in ${\mathrm{PrAgBi}}_2$. Analysis of the CEF effect using a multilevel energy scheme reveals that the ground state of ${\mathrm{PrAgBi}}_2$ consists of five singlets and two doublets. The de Haas-van Alphen (dHvA) quantum oscillations data show a single frequency with a very small cyclotron effective mass of approximately 0.11 $m_e$. A nontrivial Berry phase is also observed from the quantum oscillations data. The magnetotransport data shows linear and unsaturated magnetoresistance, reaching up to 1060% at 2 K and 9 T. Notably, there is a crossover from a weak-field quadratic dependence to a high-field linear dependence in the field-dependent magnetoresistance data. The crossover critical field $B^{*}$ follows the quadratic temperature dependence, indicating the existence of Dirac fermions. The band-structure calculation shows several Dirac-like linear band dispersion near the Fermi level and a Dirac point close to the Fermi level, located at the Brillouin zone boundary. Ab initio calculations allowed us to ascribe the observed dHvA oscillation frequency to a particular feature of the Fermi surface. Our study suggests layered ${\mathrm{PrAgBi}}_2$ is a plausible candidate for hosting the CEF effect and Dirac fermion in the Bi square net.

Hot electrons formed in a graphene crystal by high-intensity, short-duration laser pulses can exist for a time that is less than the electron-phonon energy relaxation time. During that time, electron-electron collisions cause the electrons to thermalize to a local effective temperature that propagates (diffuses) through the graphene crystal. The nonuniform nature of the electron temperature leads to a force acting on the graphene lattice. This force is the result of the electron-lattice interaction that exists even at times that are less than the electron-phonon scattering time. The force causes the lattice to deform. A Boltzmann equation description of the transient electron-lattice deformation caused by hot electrons in graphene is presented.

The nonlinear acoustic valley Hall effect (AVHE), a recently discovered novel acoustically driven phenomenon, has sparked extensive interests in valleytronics. So far, only the intrinsic contributions from band structure (Berry curvature or asymmetric energy dispersions) to nonlinear AVHE have been investigated. Here, we theoretically investigate the nonlinear AVHE from both intrinsic and extrinsic contributions in two-dimensional (2D) hexagonal massive Dirac materials with disorders based on the Boltzmann formalism and also concretely analyze the behaviors of nonlinear AVHE in disordered monolayer ${\mathrm{MoS}}_2$. It is found that the extrinsic contributions (side jump and skew scattering) can also give rise to a pure nonlinear AVHE in 2D hexagonal massive Dirac materials. Remarkably, the extrinsic mechanisms dominate the nonlinear AVHE in the disordered monolayer ${\mathrm{MoS}}_2$.

We investigate the entanglement dynamics of systems consisting of up to five qubits coupled to an optical microcavity. This is depicted by a system of excitons in strained graphene. We numerically calculate the time evolution of multiple entanglement monotones in such systems when subjected to a coherent source of photons (e.g., a laser). We propose a different way of estimating the total amount of quantum entanglement contained within a multipartite system based on the negativity which we refer to as total negativity, and to which we give clear upper and lower bounds for this quantity. We compared the results for a system of excitons in strained graphene along with two other systems which can be described by the same Hamiltonian as that for superconducting qubits coupled to a waveguide, and for trapped Rb atoms. We have shown that, depending on the physical parameters of the system, a reasonable amount of long-living entanglement can be created between the qubits. This entanglement is exempt from decay as long as the systems are being continuously pumped with coherent photons. We have reached the interesting conclusion that freely adding new qubits to the system does not, in general, increase the overall amount of entanglement created by the dynamics: there exist an optimum number of system qubits which depend on the Rabi coupling as well as the cavity decay rate for maximal entanglement. We believe that such systems are good candidates for the generation of resilient sets of long-lived partially entangled states suitable for experiments in entanglement distillation.

Topological insulators (TIs) as the focus of recent interests have reshaped our understanding of physics and materials, however, the two-dimensional (2D) weak TIs (WTIs) with gapless edge states have not been reported so far. Here we put forward that, in contrast to previously reported TIs, WTIs can emerge in two dimensions with band inversions at generic $k$ points, rather than the high-symmetry momenta. In particular, as a probable candidate for the experimental realization of 2D WTIs, we propose the stable ${\mathrm{RhBi}}_2$ monolayer with supporting evidence based on first-principles calculations. The weak topological nature is explicitly confirmed via the nonzero topological invariant $({\nu }_0;{\nu }_1{\nu }_2)=(0;01)$ and two pairs of gapless edge states along the (01) direction. Moreover, the robustness of the 2D WTIs is further confirmed by strain engineering. Our results uncover a novel nontrivial state that will provide a wonderful platform to investigate the topological phases in two dimensions.

Interaction of the laser radiation with magnetic nanostructures continuously attracts high research interest. This issue concerns the studies of surface-driven mechanisms of the magneto-optical response of multicomponent structures composed of magnetic and nonmagnetic specimen. Here we study the magnetization-induced optical second-harmonic generation in its relation to the magnetization dynamics induced in bilayer ferromagnetic/heavy metal nanofilms by the magnetic field of an intense femtosecond laser pulse. We show the appearance of odd in magnetization intensity effect in the second-harmonic generation (SHG), which correlates with the damping of the magnetization oscillations at the optical wave frequency as was predicted quite recently. The efficiency of the effect is of a few percent as compared to the nonmagnetic SHG and is the most pronounced for the so-called “forbidden” SHG geometry, i.e., for the $p$-polarized incident and reflected waves in the longitudinal magnetization scheme. This magnetization-dynamics-induced SHG contribution is shown to be anisotropic, sensitive to the angle of incidence of the probe beam, and is the largest for the CoPt films due to the maximum Gilbert damping constant.