We consider magnetic oxide/heavy metal oxide hybrid film on top of a substrate with high dielectric constant. We use the double exchange model to describe the system behavior. The interface between two oxide films produces Rashba spin-orbit interaction. The phase separation appears in such a magnetic film. Combination of the phase separation and spin-orbit coupling leads to formation of electrically charged magnetic clusters with skyrmions. We show that such clusters have both electrical and topological charges. Importantly, clusters with sizes suitable for skyrmions formation may occur only for substrate with a high dielectric constant.

Recently, “Pascal's triangle model” constructed with $\mathrm{U}\left(1\right)$ rotor degrees of freedom was introduced and it was shown that ($\mathit{i}$) this model possesses an infinite series of fractal symmetries and ($\mathit{ii}$) it is the parent model of a series of $Z_p$ fractal models each with its own distinct fractal symmetry. In this work we discuss a multicritical point of Pascal's triangle model that is analogous to the Rokhsar-Kivelson point of the better known quantum dimer model. We demonstrate that the expectation value of the characteristic operator of each fractal symmetry at this multicritical point decays as a power law of space and this multicritical point is shared by the family of descendent $Z_p$ fractal models. Afterwards, we generalize our discussion to a $(3+1)d$ model termed “Pascal's tetrahedron model” that has both planar and fractal subsystem symmetries. We also establish a connection between Pascal's tetrahedron model and the $\mathrm{U}\left(1\right)$ Haah's code.

We search for short-range Hamiltonians of finite spin-1 kagome systems, maximizing the overlaps with lattice Moore-Read states. Our starting point is an exact, long-range parent Hamiltonian for such a state on a finite plane, obtained from conformal field theory. A truncation procedure is applied to it, which retains only short-range terms and makes it easy to define the Hamiltonian on a torus. Finally, the remaining coefficients are optimized, to yield maximized overlaps between exact diagonalization results and model ground states. In the best cases, the squared overlaps exceed 0.9 and 0.8 for the three lowest states of 12- and 18-site systems, respectively, suggesting that the obtained Hamiltonians are good parent Hamiltonians for a non-Abelian topological order.

The recent observation of superconductivity in an infinite-layer and quintuple-layer nickelate within the same $R_{n+1}{\mathrm{Ni}}_n{\mathrm{O}}_{2n+2}$ series ($R$ = rare-earth, $n=2-\infty$, with $n$ indicating the number of ${\mathrm{NiO}}_2$ layers along the $c$ axis), unlocks their potential to embody a whole family of unconventional superconductors. Here, we systematically investigate the many-body electronic structure of the layered nickelates (with $n=2-6,\infty$) within a density-functional theory plus dynamical mean-field theory framework and contrast it with that of the known superconducting members of the series and with the cuprates. We find that many features of the electronic structure are common to the entire nickelate series, namely, strongly correlated Ni-$d_{x^2-y^2}$ orbitals that dominate the low-energy physics, mixed Mott-Hubbard/charge-transfer characteristics, and $R$($5d$) orbitals acting as charge reservoirs. Interestingly, we uncover that the electronic structure of the layered nickelates is highly tunable as the dimensionality changes from quasi-two-dimensional to three-dimensional as $n\to \infty$. Specifically, we identify the tunable electronic features to be: the charge-transfer energy, presence of $R\left(5d\right)$ states around the Fermi level, and the strength of electronic correlations.

We analyze the phase diagram of a topological insulator model including antiferromagnetic interactions in the form of an extended Su-Schrieffer-Heeger model. To this end, we employ a recently introduced operational definition of topological order based on the ability of a system to perform topological error correction. We show that the necessary error correction statistics can be obtained efficiently using a Monte Carlo sampling of a matrix product state representation of the ground state wave function. Specifically, we identify two distinct symmetry-protected topological phases corresponding to two different fully dimerized reference states. Finally, we extend the notion of error correction to classify thermodynamic phases to those exhibiting local order parameters, finding a topologically trivial antiferromagnetic phase for sufficiently strong interactions.

Electronic nematicity is rarely observed as an isolated instability of a correlated electron system. Instead, in iron pnictides and in certain cuprates and heavy-fermion materials, nematicity is intertwined with an underlying spin-stripe or charge-stripe state. As a result, random strain, ubiquitous in any real crystal, creates both random-field disorder for the nematic degrees of freedom and random-bond disorder for the spin or charge ones. Here, we put forward an Ashkin-Teller model with random Baxter fields to capture the dual role of random strain in nematic systems for which nematicity is a composite order arising from a stripe state. Using Monte Carlo to simulate this random Baxter-field model, we find not only the expected breakup of the system into nematic domains, but also the emergence of nontrivial disorder-promoted magnetic correlations. Such correlations enhance and tie up the fluctuations associated with the two degenerate magnetic stripe states from which nematicity arises, leaving characteristic signatures in the spatial profile of the magnetic domains, in the configurational space of the spin variables, and in the magnetic noise spectrum. We discuss possible experimental manifestations of these effects in iron-pnictide superconductors. Our work establishes the random Baxter-field model as a more complete alternative to the random-field Ising model to describe complex electronic nematic phenomena in the presence of disorder.

We have investigated the nonreciprocal electrical transport, that is a nonlinear resistance effect depending on the current direction, in the multiferroic Rashba semiconductor (Ge,Mn)Te. Due to the coexistence of ferromagnetic and ferroelectric orders, (Ge,Mn)Te provides a unique platform for exploring the nonreciprocal electrical transport in a bulk form. (Ge,Mn)Te thin films shows a large nonreciprocal resistance compared to GeTe, the nonmagnetic counterpart with the same crystal structure. The magnetic-field-angle dependence of the nonreciprocal resistance is maximized when magnetic field is orthogonal to both current and electric polarization, in accord with the symmetry argument. From the analysis of temperature and magnetic field dependence, we deduce that inelastic scatterings of electrons mediated by magnons dominantly contribute to the observed nonreciprocal response. Furthermore, the nonreciprocal resistance is significantly enhanced by lowering hole density. The Fermi level dependence is attributed to the deformation of the Rashba band in which the spin-momentum locked single Fermi surface appears by exchange field from the in-plane magnetization. The present study provides a key insight to the mechanisms of novel transport phenomena caused by the interplay of ferroelectric and ferromagnetic orders in a semiconductor.

Two-dimensional (2D) semiconductors have demonstrated great potential for next-generation electronics and optoelectronics. An important property for these applications is the phonon-limited charge carrier mobility. The common approach to calculate the mobility from first principles relies on the interpolation of the electron-phonon coupling (EPC) matrix. However, it neglects the scattering by the quadrupoles generated by phonons, limiting its accuracy. Here we present a first-principles method to incorporate the quadrupole scattering, which results in a much better interpolation quality and thus a more accurate mobility as exemplified by monolayer $\mathrm{Mo}{\mathrm{S}}_2$ and InSe. This method also allows for a natural incorporation of the effects of the free carriers, enabling us to efficiently compute the screened EPC and thus the mobility for electrostatically doped semiconductors. Particularly, we find that the electron mobility of InSe is more sensitive to the carrier concentration than that of $\mathrm{Mo}{\mathrm{S}}_2$ due to the stronger long-range scattering in intrinsic InSe. With increasing electron concentration, the InSe mobility can reach $\sim 4$ times the intrinsic value, then decrease owing to the involvement of heavier electronic states. Our work provides accurate and efficient methods to calculate the phonon-limited mobility in the intrinsic and electrostatically doped 2D materials, and improves the fundamental understanding of their transport mechanism.

Quantum hydrodynamics is the emergent classical dynamics governing transport of conserved quantities in generic strongly interacting quantum systems. Recent matrix product operator methods [1,2] have made simulations of quantum hydrodynamics in $1+1\mathrm{D}$ tractable, but they do not naturally generalize to $2+1\mathrm{D}$ or higher, and they offer limited guidance as to the difficulty of simulations on quantum computers. Near-Clifford simulation algorithms are not limited to one dimension, and future error-corrected quantum computers will likely be bottlenecked by non-Clifford operations. We therefore investigate the non-Clifford resource requirements for simulation of quantum hydrodynamics using mana, a resource theory of non-Clifford operations. For infinite-temperature starting states, we find that the mana of subsystems quickly approaches zero, while for starting states with energy above some threshold the mana approaches a nonzero value. Surprisingly, in each case the finite-time mana is governed by the subsystem entropy, not the thermal state mana; we argue that this is because mana is a sensitive diagnostic of finite-time deviations from canonical typicality.

We carry out first-principles density-functional-theory calculations to investigate the possibility of nonadiabatic switching (purely electronic hopping without structural change) in charge-order-induced ferroelectrics. In charge-order-induced ferroelectrics, polarization switching can in principle occur through nonadiabatic interionic electron hopping with an ultrafast speed. However, lattice relaxation for a specific charge-ordering state can “lock” that state in, making nonadiabatic switching to a different charge-ordering variant energetically prohibitive; whether nonadiabatic switching on electronic time scales can occur thus depends on the strength of lattice-electron coupling. In this work, we propose a simple model predicting the possibility of nonadiabatic switching based on structural analysis. Specifically, we point out that electric field driven nonadiabatic electron hopping is possible in charge-order-induced ferroelectrics whose primary coupling mode is off-centering displacement, rather than polyhedral breathing. We carry out calculations and analysis on three different prototype charge-ordering materials, including the (theoretically designed) (${\mathrm{SrVO}}_3{)}_1{\left({\mathrm{LaVO}}_3\right)}_1$ superlattice, ${\mathrm{LuFe}}_2{\mathrm{O}}_4$, and ${\mathrm{Fe}}_3{\mathrm{O}}_4$. All the results support our theory and are also in accord with experimental observations. These results show the critical role of electron-lattice coupling in nonadiabatic polarization switching in charge-order-induced ferroelectrics, providing guidance for the design and discovery of “electronic ferroelectrics” with ultrafast polarization switching on electronic rather than lattice time scales.

Traditional finite-temperature Kohn-Sham density functional theory (KSDFT) based on the diagonalization (DG) method has an unfavorable scaling with respect to the electron number or at high temperatures. The evaluation of the ground-state density in KSDFT can be replaced by the Chebyshev trace (CT) method. In addition, the use of stochastic orbitals within the CT method leads to the stochastic density functional theory [Phys. Rev. Lett. 111, 106402 (2013)] (SDFT) and its improved theory, mixed stochastic-deterministic density functional theory [Phys. Rev. Lett. 125, 055002 (2020)] (MDFT). We have implemented the above four methods based on the plane-wave basis set within the first-principles package ABACUS. In addition, the four methods are adapted to the norm-conserving pseudopotentials and periodic boundary conditions with the use of $k$-point sampling in the Brillouin zone. By testing the Si and C systems from the DG method as benchmarks, we systematically evaluate the accuracy and efficiency of the CT, SDFT, and MDFT methods by examining a series of physical properties, which include the electron density, free energy, atomic forces, stress, and density of states. We conclude that the CT, SDFT, and MDFT methods not only reproduce the DG results with a sufficient accuracy but also exhibit several advantages over the DG method. We expect these methods can be of great help in studying high-temperature and large-size extended systems such as warm dense matter and dense plasmas.

Integrating two-dimensional materials into van der Waals heterostructures (vdWHs) is considered to be an efficient strategy for multifunctional devices. Here, the $m\text{−}\mathrm{GaS}/n\text{−}{\mathrm{MoTe}}_2$ (${\mathrm{WTe}}_2$) multilayer vdWHs are designed to explore possible characteristics through engineering the electric field, strain, and layer combination m/n. For the most stable $\mathrm{GaS}/{\mathrm{MoTe}}_2$ (${\mathrm{WTe}}_2$) bilayer vdWHs obtained by global search with direct band structure and straddling gap, the proper compression strain and positive electric field regulates the band structure from straddling gap to staggered case. Particularly, the $m\text{−}\mathrm{GaS}/n\text{−}{\mathrm{WTe}}_2$ multilayer vdWHs have the straddling band alignment when the layer number of GaS is 1L $(m=1)$, while it can be transferred to staggered case with the $m>1$ due to the quantum confinement effect. In addition, the $\mathrm{GaS}/{\mathrm{MoTe}}_2$ vdWHs can be used as highly efficient solar cells with power conversion efficiency up to 27%. Also, the photoresponsivity and external quantum effects are increased from 0.048 (8%) to 0.18 A/W (42%) for the multilayer vdWHs. These results indicate that the $m\text{−}\mathrm{GaS}/n\text{−}{\mathrm{MoTe}}_2$ (${\mathrm{WTe}}_2$) multilayer vdWHs can be taken as reconfigurable system in highly efficient solar cells and photodetectors.

Cuprous iodide (CuI) is a wide bandgap (∼3.1 eV) semiconductor of great recent interest because of its high transparency, high hole conductivity, large exciton binding energy, and sizable spin-orbit interaction. However, studies on single-crystalline thin films have been scarcely reported. Here, we report on the epitaxial growth of single-crystalline CuI films and their optical characterization to elucidate the modification of band structure caused by the anisotropic strain. Thin films were grown by molecular beam epitaxy on nearly lattice-matched (only 0.1%-mismatched) InAs substrates with (001), (110), and (111) crystal orientation, yielding pseudomorphic structures with high lattice coherence and atomic-level flatness. Both reflectance and photoluminescence spectra exhibit sharp exciton profiles over a wide temperature range. We assign the exciton transition energies to deduce the band structure modifications associated with the epitaxial strain varying with temperature and growth orientation. Furthermore, we determine the deformation potentials which relate the strain to the band structure modification. The systematic studies of the strain effect for CuI thin films on various substrate planes will pave the way for the future optoelectronic application of CuI-based heterostructures.

Black arsenic (BAs) has emerged to be an interesting elemental layered material after graphite and black phosphorus (BP), which can be exfoliated to yield high-quality two-dimensional flakes. Transport measurements have revealed its strong in-plane anisotropy, giant Stark effect, and strong spin-orbital coupling, all resulting from its special electronic properties. On the other hand, previous synthetic analysis indicated that the pure BAs phase is unstable and could only be stabilized by a substantial percentage of impurities. Thus, a microscopic study of its structural and electronic properties is important for understanding this material. Here, we use scanning tunneling microscopy and spectroscopy assisted with first-principles calculations to investigate natural BAs at the atomic level. A puckered lattice structure like that of BP is measured. A bandgap of $\sim 0.29\mathrm{eV}$ is detected with the Fermi level located close to the conduction band. The most common defects form parallel stripes along a specific crystal direction and are shown to be the possible origin of the $n\text{−}\mathrm{type}$ doping in the natural BAs. These results provide valuable information for further study of BAs.

The surface Fermi arc, as a hallmark of Weyl semimetals (WSMs), has been well known in current research, but it remains a challenge to unveil novel phenomena associated with the Fermi arc. Here, in WSMs, namely, the photoinduced transition between the bulk states and the Fermi arc. We find this process is significant and can lead to a large effective three-dimensional shift current on the boundaries with the Fermi arc in wide terahertz range. Moreover, due to the low symmetry of the boundaries, the surface photogalvanic effect predicted here can appear in a large class of WSMs that can not have bulk shift current. Hence, our work not only unveils a hidden photogalvanic effect in WSMs but also suggests that all the WSMs are promising material candidates for developing efficient terahertz photodetectors.

The negligible intrinsic spin-orbit coupling (SOC) in graphene can be enhanced by proximity effects in stacked heterostructures of graphene and transition metal dichalcogenides (TMDCs). The composition of the TMDC layer plays a key role in determining the nature and strength of the resultant SOC induced in the graphene layer. Here, we study the evolution of the proximity–induced SOC as the TMDC layer is deliberately defected. Alloyed $\mathrm{G}/{\mathrm{W}}_{\chi }{\mathrm{Mo}}_{1-\chi }{\mathrm{Se}}_2$ heterostructures with diverse compositions ($\chi$) and defect distributions are simulated using density functional theory. Comparison with continuum and tight-binding models allows both local and global signatures of the metal-atom alloying to be clarified. Our findings show that, despite some dramatic perturbation of local parameters for individual defects, the low-energy spin and electronic behavior follow a simple effective medium model which depends only on the composition ratio of the metallic species in the TMDC layer. Furthermore, we demonstrate that the topological state of such alloyed systems can be feasibly tuned by controlling this ratio.

We study $\mathbb{C}{P}^2$ skyrmion crystals in the ferromagnetic $\mathrm{SU}\left(3\right)$ Heisenberg model with a generalization of the Dzyaloshinskii-Moriya interaction and the Zeeman term. The model possesses two different types of skyrmion crystals with unit skyrmions that can be interpreted as bound states of two half-skyrmions or four quarter-skyrmions. Our study on $\mathbb{C}{P}^2$ skyrmion crystals opens up the possibility for useful future applications since $\mathbb{C}{P}^2$ skyrmions have more degrees of freedom than the usual $\mathbb{C}{P}^1$ (magnetic) skyrmions.

The high-pressure melting diagram of iron is a vital ingredient for the geodynamic modeling of planetary interiors. Nonetheless, available data for molten iron show an alarming discrepancy. Herein, we propose an efficient one-phase approach to capture the solid-liquid transition of iron under extreme conditions. Our basic idea is to extend the statistical moment method to determine the density of iron in the TPa region. On that basis, we adapt the work-heat equivalence principle to appropriately link equation-of-state parameters with melting properties. This strategy allows explaining cutting-edge experimental and ab initio results without massive computational workloads. Our theoretical calculations would be helpful to constrain the chemical composition, internal dynamics, and thermal evolution of the Earth and super-Earths.

A recent study [H. Hao and F. Semperlotti, Phys. Rev. B 104, 104303 (2021)] investigated the dynamic behavior of an infinite one-dimensional (1D) thermoacoustic waveguide (TAWG) and illustrated its ability to sustain nonreciprocal and near zero-index sound propagation behavior; these properties can be very beneficial in the design of acoustic devices, including acoustic diodes, amplifiers, and cloaks. Nevertheless, it is critical to realize that when this concept is implemented in a finite-length waveguide, dynamic instabilities may occur and either drastically reduce or completely hinder the ability of the TAWG to control and manipulate sound. In this paper, we uncover and investigate the occurrence of either evanescent or intrinsic thermoacoustic (ITA) modes in a 1D TAWG with anechoic terminations. The stability analysis clearly distinguishes these two types of evanescent modes and highlights their different origin rooted in either acoustic or thermoviscous effects. Numerical results reveal that ITA modes in anechoic-terminated TAWG are strictly connected to the acoustic-driven evanescent modes, and evolve towards unstable modes as the TA coupling strength is increased. This study may have important implications for the practical design of novel acoustic manipulating devices enabled by TA coupling elements. The conclusions drawn in this study may also shed lights on the effective suppression of instabilities in TAWGs.

We demonstrate a few unique dynamical properties of point-gap Weyl semimetal, an intrinsic non-Hermitian topological phase in three dimensions. We consider a concrete model where a pair of Weyl points reside on the imaginary axis of the complex energy plane, opening a point gap characterized by a topological invariant, the three-winding number $W_3$. This gives rise to surface spectra and dynamical responses that differ fundamentally from those in Hermitian Weyl semimetals. First, we predict a time-dependent current flow along the magnetic field in the absence of an electric field, in sharp contrast to the current driven by the chiral anomaly, which requires both electric and magnetic fields. Second, we reveal a type of boundary-skin mode in the wire geometry which becomes localized at two corners of the wire cross section. We explain its origin and show its experimental signatures in wave-packet dynamics.