Nonuniform strain in graphene can induce a pseudomagnetic field (PMF) preserving time-reversal symmetry, generating pseudo-Landau levels under zero real magnetic field (MF). The different natures between PMF and real MF lead to the counterpropagating valley-polarized edge states under the PMF and unidirectionally chiral edge states under the real MF. In this work, we find, due to the valley mixing on the armchair edges, the quantum valley Hall edge states only exist at the zigzag edges but not at armchair edges in a uniaxial strained graphene, very different from the case in which chiral quantum Hall edge states exist at all edges in pristine graphene under a real MF. We theoretically demonstrate it through the wave-function distributions, multiterminal transport measurements and the electron local occupations, respectively. The interface state in a $p\text{−}n$ junction under PMF is further proposed to transport electrons between the conductive zigzag boundaries, which could be used as a valley-polarized single-pole double throw switch.

Doping nonmagnetic Ga atoms into Fe leads to the enhancement in magnetostriction by ∼10 times in the FeGa solid solutions; the fundamental mechanism of the anomalous enhancement has attracted substantial attention. However, current experimental methods are difficult to reveal the origin because of their inability in the electronic and atomic scales. In this work, we utilized first-principles calculations to unveil the origin of giant magnetostriction in FeGa solid solutions. Ga doping results in the random substitution of Fe by Ga in the disordered $A2$ matrix and the formation of $L{6}_0$ nanoheterogeneities simultaneously. The former weakens the strength of Fe–Fe metallic bonding framework, thus leading to the lattice softening as presented by the sharp reduction in elastic constant $c^{\prime } [c^{\prime }=\left(c_{11}-c_{12}\right)/2$]. The latter strengthens the magnetoelastic coupling effect by regulating the density of states of $3d$ orbits of Fe atoms inside and adjacent to the nanoheterogeneities, resulting in the 3 times larger magnetoelastic coupling coefficient $-b_1$. The two effects synergistically offer the giant magnetostriction in FeGa solid solutions based on the relationship of ${\lambda }_{001}=-\left(b_1/3c^{\prime }\right)$. Furthermore, the influence of elemental doping, including Co, Ni, P, and Tb, on magnetostriction is systematically studied. It is demonstrated that Tb is the sole alloying element which can enhance the magnetoelastic coupling effect strongly, allowing FeGa-Tb supercell to present an ultrahigh magnetostriction of 738 ppm, which is over 2 times larger than that of the FeGa supercells. This work offers insights into the origin of giant heterogeneous magnetostriction in Fe-based solid solutions, which benefits the development of high-performance FeGa-based magnetostrictive materials.

The cobalt atoms within the crystal structure of ${\mathrm{Co}}_3{\mathrm{V}}_2{\mathrm{O}}_8$ arrange themselves into kagome staircase lattices. Our low-temperature synchrotron diffraction studies confirm a distortion in kagome lattices along the [010] direction associated with the anomalous thermal expansion of the unit cell volume below $\sim 180$ K. At this temperature, a structural transition to a polar $Aba2$ space group from the high-temperature structure is suggested. This transition is further confirmed by Raman spectroscopy and is associated with the ferroelectric order at 180 K ($T_{\mathrm{FE}}$). Below $T_{\mathrm{FE}}$, a significant linear magnetoelectric (ME) coupling is realized despite long-range magnetic order occurring below $\sim 11$ K. Thus, ME coupling is linked to the distortion in the kagome lattice structure formed by the Co atoms. These correlations provide an opportunity for manipulating ME coupling at elevated temperatures. The compound exhibits a highly promising magnetocaloric effect in proximity to its magnetic order, constituting another appealing outcome. This characteristic is interesting for the exploration of rare-earth-free magnetocaloric materials.

We show that ferromagnetic interactions can enhance the adiabatic performance of a quantum spin chain engine at low temperatures. The enhancement in work output is particular pronounced, increasing exponentially with interaction strength. The performance enhancement occurs in the paramagnetic phase and is qualitatively explained by considering just the ground and first excited state, in which case the system exhibits bipartite entanglement. As the temperature is increased, thermal occupation of higher energy states diminishes performance. We find that these thermal fluctuations are smallest for long-range interactions, resulting in the highest efficiency. Diabatic work extraction degrades performance due to quantum friction. We identify an approximate, experimentally realisable counterdiabatic drive that can mitigate friction for weak interactions.

Random quantum circuits are paradigmatic models of minimally structured and analytically tractable chaotic dynamics. We study a family of Floquet unitary circuits with Haar random $U\left(1\right)$ charge conserving dynamics; the minimal such model has nearest-neighbor gates acting on spin-1/2 qubits, and a single layer of even/odd gates repeated periodically in time. We find that this minimal model is not robustly thermalizing at numerically accessible system sizes, and displays slow subdiffusive dynamics for long times. We map out the thermalization dynamics in a broader parameter space of charge conserving circuits, and understand the origin of the slow dynamics in terms of proximate localized and integrable regimes in parameter space. In contrast, we find that small extensions to the minimal model are sufficient to achieve robust thermalization; these include (i) increasing the interaction range to three-site gates, (ii) increasing the local Hilbert space dimension by appending an additional unconstrained qubit to the conserved charge on each site, or (iii) using a larger Floquet period comprised of two independent layers of gates. Our results should inform future studies of charge conserving circuits, which are relevant for a wide range of topical theoretical questions.

Twisted magnons (TMs) have great potential applications in communication and computing owing to the orbital angular momentum degree of freedom. Realizing the unidirectional propagation of TMs is the key to designing functional magnonics devices. Here we theoretically study the propagation of TMs in one-dimensional magnetic nanodisk arrays. By performing micromagnetic simulations, we find that the one-dimensional nanodisk array exhibits a few bands due to the collective excitations of TMs. A simple model of the exchange interaction is proposed to explain the emerging multiband structure, and theoretical results agree well with micromagnetic simulations. Interestingly, for a zigzag structure, the dispersion curves and propagation images of TMs show obvious nonreciprocity for a specific azimuthal quantum number ($l$), which originates from a geometric effect depending on the phase difference of TMs and the relative angle between two adjacent nanodisks. Utilizing this feature, one can conveniently realize the unidirectional propagation of TMs with arbitrary nonzero $l$. Our work provides important theoretical references for controlling the propagation of TMs.

Exhaustive study of topological semimetal (TSM) phases of matter in equilibriated electonic systems and myriad extensions has built upon the foundations laid by earlier introduction and study of Weyl semimetals, with broad applications in topologically protected quantum computing, spintronics, and optical devices. We extend recent introduction of multiplicative topological phases to find previously overlooked TSM phases of electronic systems in equilibrium, with minimal symmetry protection. We show these multiplicative TSM (MTSM) phases exhibit rich and distinctive bulk-boundary correspondence and response signatures that greatly expand understanding of consequences of topology in condensed matter settings, such as the limits on Fermi arc connectivity and structure, and transport signatures such as the chiral anomaly. In this paper, we therefore lay the foundation for extensive future study of MTSMs.

Higher-order Weyl semimetal (HOWSM) is a fascinating topological phase that connects the nontrivial higher-order topology and Weyl semimetal. In this paper, we introduce a novel phase termed higher-order double-Weyl semimetals (HODWSMs) through the application of symmetry analysis and a minimal tight-binding model. This phase is notable for its quadratic double-Weyl nodes located in the $k_z=0$ plane and nontrivial higher-order topology in other planes. Specifically, within this phase, there is a sole pair of Weyl nodes, distinguished by chiral charges of $+2$ and $-2$, respectively. The emergence of these nodes can be attributed to the combined effect of $C_4$ rotation symmetry and time-reversal symmetry, whereas the higher-order topology stems from the filling anomaly. Through first-principles calculations, we propose that ${\mathrm{LaRhC}}_2$, an experimentally synthesized material, serves as a prototypical crystalline candidate for observing this unique HODWSM phase in its optic phonons. Additionally, further calculations demonstrate that the HODWSM phase exhibits direction-dependent surface and hinge states, providing distinctive features for future experimental detection of this intriguing and nontrivial topological phase.

We analyze the two-body spectrum within the Hofstadter-Hubbard model on a square lattice through an exact variational ansatz and study the topological properties of its low-lying two-body bound-state branches. In particular, we discuss how the Hofstadter-Hubbard butterfly of the two-body branches evolves as a function of onsite interactions and how to efficiently calculate their Chern numbers using the Fukui-Hatsugai-Suzuki approach. Our numerical results are fully consistent with the simple picture that appears in the strong-coupling limit, where the attraction between fermions forms a composite boson characterized by an effective hopping parameter and an effective magnetic-flux ratio.

We investigate the mechanisms responsible for the distinct characteristics of certain relaxor ferroelectrics, which display pinched polarization hysteresis loops and recoverable electrostrains, in contrast to the rectangular-like polarization hysteresis loops and irrecoverable butterfly-shaped electrostrains observed in typical ferroelectrics. Despite the large number of experimental reports on these materials, the origin of their recoverable electrostrains has remained elusive until now. Using a phase-field model, we study a doped ferroelectric system, considering both local electric fields and local phase-transition temperature variations induced by the local compositional heterogeneity. The directions of local electric fields are randomly distributed along one of the four directions of the spontaneous polarizations in the system. The resulting phase diagram reveals the existence of both normal ferroelectrics and relaxor ferroelectrics, with pinched polarization hysteresis loops and recoverable electrostrains appearing only in the latter. Our simulations shed light on the crucial role of strong local electric fields along spontaneous polarization directions caused by point defects in facilitating nucleation of domains with polarization along the same direction. This, in turn, explains the recoverability of the polarization and electrostrain in certain relaxors, as these local fields can help restore the initial domain-structure, polarization, and strain. These findings provide new insights into the origin of recoverable electrostrains in relaxors, which could have implications for the design of relaxors with large recoverable electrostrains.

In this constantly expanding and evolving era of advanced technology, there is great demand for a compound that boasts a plethora of exotic properties. To procure such a compound, we conducted a thorough analysis of the lattice and electronic properties of several Th-based compounds using first-principle calculations. A Dirac-like crossing displaying nodal line characteristics has been observed in the phonon spectrum of ${\mathrm{ThAs}}_2$, exhibiting nontriviality that has been further confirmed by a nonzero value of the Berry phase. In the analysis of the electronic structure of all the compounds, we have detected nontrivial topological features that were manifested by means of gap plane and ${\mathbb{Z}}_2$ calculations. Moreover, a thorough examination of the compounds further revealed the presence of nodal surfaces, which have been analyzed for their intricate symmetry. The Fermi surface of ${\mathrm{ThAs}}_2$ has been scrutinized for nesting properties through the computation of the real and imaginary components of Lindhard susceptibility, which have shown peaks at the same wave vector, indicating the possibility of a charge density wave in this compound. Furthermore, the application of a 5 T magnetic field has revealed a giant negative magnetoresistance in ${\mathrm{ThAs}}_2$ at 10 K. The coexistence of topological fermions and bosons in the same compound is a rare phenomenon and, combined with the probable presence of charge density waves and negative magnetoresistance, this provides an in-depth, comprehensive understanding of its physical properties and also presents a promising platform for further experimental verifications.

We revisit the problem of a two-dimensional trion in an external magnetic field. We demonstrate that the approximations used previously for finding the energy spectrum of this system break down in the experimentally accessible range of magnetic fields. It is shown that the neglect of the Coulomb-induced mixing of different Landau levels corresponding to noninteracting particles leads to a strong underestimation of the trion binding energies even at extremely high magnetic fields (hundreds of Tesla). Moreover, proper account of the Coulomb effects for certain values of the parameters can lead to the appearance of additional discrete trion states, which were overlooked previously. Finally, we provide a database of the matrix elements necessary for calculation of the magnetotrion spectra for a wide class of materials.

An optical field around regular polygon metal nanostructures excited by circularly polarized light can exhibit rotationally displaced intensity distributions. Although this phenomenon has been recognized, its underlying mechanisms have not been sufficiently explained. Herein, finite-difference time-domain simulations and model analyses reveal that the rotationally displaced optical intensity distribution can be generated when each of the linear polarization components that constitute circular polarization excites a superposition of multiple modes. The proposed model reasonably explains the rotationally displaced patterns for a square nanoantenna and other regular-polygon nanoantennas.

Magnetic topological insulators in the quantum anomalous Hall regime host ballistic chiral edge channels. When proximitized by an $s$-wave superconductor, these edge states offer the potential for realizing topological superconductivity and Majorana bound states without the detrimental effect of large externally applied magnetic fields on superconductivity. Realizing well-separated unpaired Majorana bound states requires magnetic topological insulator ribbons with a width of the order of the transverse extent of the edge state, however, which is expected to bring the required ribbon width down to around $100\mathrm{nm}$. In this regime, it is known to be extremely difficult to retain the ballistic nature of chiral edge channels and realize a quantized Hall conductance. In this paper, we study the impact of disorder in such magnetic topological insulator nanoribbons and compare the fragility of ballistic chiral edge channels with the stability of Majorana bound states when the ribbon is covered by a superconducting film. We find that the Majorana bound states exhibit greater robustness against disorder than the underlying chiral edge channels.

The eigenstate thermalization hypothesis (ETH) is a successful theory that establishes the criteria for ergodicity and thermalization in isolated quantum many-body systems. In this work, we investigate the thermalization properties of a spin-$1/2$ XXZ chain with linearly inhomogeneous interactions. We demonstrate that introduction of the inhomogeneous interactions leads to an onset of quantum chaos and thermalization, which, however, becomes inhibited for sufficiently strong inhomogeneity. To exhibit ETH, and to display its breakdown upon varying the strength of interactions, we probe statistics of energy levels and properties of matrix elements of local observables in eigenstates of the inhomogeneous XXZ spin chain. Moreover, we investigate the dynamics of the entanglement entropy and the survival probability which further evidence the thermalization and its breakdown in the considered model. We outline a way to experimentally realize the XXZ chain with linearly inhomogeneous interactions in systems of ultracold atoms. Our results highlight a mechanism of emergence of ETH due to insertion of inhomogeneities in an otherwise integrable system and illustrate the arrest of quantum dynamics in the presence of strong interactions.

The time-evolving matrix product operators (TEMPO) method, which makes full use of the Feynman-Vernon influence functional, is the state-of-the-art tensor network method for bosonic impurity problems. However, for fermionic impurity problems the Grassmann path integral prohibits application of this method. We develop Grassmann time-evolving matrix product operators, a full fermionic analog of TEMPO, that can directly manipulates Grassmann path integrals with similar numerical cost as the bosonic counterpart. We further propose a zipup algorithm to compute expectation values on the fly without explicitly building a single large augmented density tensor, which boosts our efficiency on top of the vanilla TEMPO. Our method has a favorable complexity scaling over existing tensor network methods, and we demonstrate its performance on the nonequilibrium dynamics of the single-impurity Anderson models. Our method solves the long-standing problem of turning Grassmann path integrals into efficient numerical algorithms, which could significantly change the application landscape of tensor network based impurity solvers, and could also be applied for broader problems in open quantum physics and condensed matter physics.

The stochastic series expansion (SSE) quantum Monte Carlo method with directed loops is very efficient for spin and boson systems. The Heisenberg model and its generalizations, such as the $J{Q}_2$ model, are extensively simulated via this method. When introducing magnetic field in these models, the SSE method always combines the field with the diagonal part of the Heisenberg interactions (${S_i}^z{S_j}^z$) and take them as the new diagonal operators. In general, this treatment is reasonable. However, when studying Hamiltonians, which have other interactions or even do not contain the Heisenberg interactions, this general treatment will not be efficient or even not work. We suggest that when doing directed-loop simulations, the magnetic field can be put into other interactions. This treatment, in some cases, improves the simulation efficiency. Using the $J{Q}_2$ model with magnetic field as an example, we here demonstrate this SSE method. Such treatment significantly improves the efficiency when the $Q_2$ interactions are large. The autocorrelations are reduced a lot compared to the previous approach. In addition, we argue that we can divide the magnetic field into two parts and combine them with both the $J$ and $Q$ operators respectively. This treatment also improves the simulation efficiency. The underlying mechanism is that these two SSE methods can utilize the main part or even all part of operators in operator products to do the directed-loop updates. Such idea can also be applied to other models with magnetic field and it will speed up the simulations.

Using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and density functional theory (DFT), we demonstrate the formation of quasicrystalline gallium adlayer on icosahedral ($i$)-Al-Pd-Mn. Quasiperiodic motifs are evident in the STM topography images, including the Ga white flower (GaWF) and $\tau$ inflated GaWF ($\tau$-GaWF), where $\tau$ is the golden mean. A larger and more complicated ring motif is also identified, comprised of a bright center and an outer ring of pentagons. The fast Fourier transform of the STM images exhibits distinct quasiperiodic spots, thereby establishing quasiperiodicity on a length scale of $\sim 350\mathrm{nm}$. Based on our DFT calculations, the preferred adsorption sites of Ga on $i$-Al-Pd-Mn are determined to be either the Mn atoms at the center of the Penrose P1 tile or the vertices of the P1 tile containing Pd atoms at the center of a cluster of five Al atoms (5-Al). The GaWF motif is modeled by an inner six-atom Ga cluster (6-Ga) around the central Mn atom and an outer ring of five Ga atoms adsorbed at the centers of the 5-Al clusters, both having pentagonal symmetry. The $\tau$-GaWF motif is modeled by the 6-Ga arranged on the $\tau$-P1 tiling, while the ring motif is modeled by Ga atoms adsorbed at the center of 5-Al clusters above a Pd atom. The side lengths and diameters of the GaWF, $\tau$-GaWF, and the ring motifs are $\tau$ scaled and show excellent agreement with the DFT-based models. An additional indication of the quasiperiodic characteristics of the Ga monolayer is the fivefold LEED patterns that were detected throughout the entire range of beam energy that was measured.

We report on the temperature dependence of the spatially modulated spin-polarization amplitude $\mathrm{\Delta }{K}_{\text{spin}}$, which is a hallmark of the superconducting Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. For that, we use ${}^{13}\mathrm{C}$ nuclear magnetic resonance (NMR) spectroscopy performed on the organic conductor ${\beta }^{\prime \prime }\text{−}{\left(\mathrm{ET}\right)}_2{\mathrm{SF}}_5{\mathrm{CH}}_2{\mathrm{CF}}_2{\mathrm{SO}}_3$. From a comparison of our experimental results to a comprehensive modeling of the ${}^{13}\mathrm{C}$ NMR spectra, we determine the evolution of $\mathrm{\Delta }{K}_{\text{spin}}$ upon condensation of the FFLO state. Further, the modeling of the spectra in the superconducting phase allows to quantify the decrease of the average spin susceptibility, stemming from the spin-singlet coupling of the superconducting electron pairs in the FFLO state of ${\beta }^{\prime \prime }\text{−}{\left(\mathrm{ET}\right)}_2{\mathrm{SF}}_5{\mathrm{CH}}_2{\mathrm{CF}}_2{\mathrm{SO}}_3$.