We propose and theoretically investigate a novel Maxwell's demon implementation based on the spin-momentum locking property of topological matter. We use nuclear spins as a memory resource which provides the advantage of scalability. We show that this topological information device can ideally operate at the Landauer limit; the heat dissipation required to erase one bit of information stored in the demon's memory approaches $k_{B}Tln2$. Furthermore, we demonstrate that all available energy, $k_{B}Tln2$ per one bit of information, can be extracted in the form of electrical work. Finally, we find that the current-voltage characteristic of topological information device satisfy the conditions of an ideal memristor.

Trimeron lattice excitations in single crystalline magnetite, in the form of $c$ axis switching (i.e., the reorganization of the lattice caused by an external magnetic field) at temperatures below the Verwey temperature $T_{\mathrm{V}}$ are observed by magnetization experiments. These excitations exhibit strong sensitivity to doping (with Zn, Al, and Ti), nonstoichiometry, and hydrostatic pressure $\left(p<1.2\mathrm{GPa}\right)$. The considered indicators of the axis switching (AS) are the switching field $B_{\mathrm{sw}}$, the energy density needed to switch the axis $E_{\mathrm{sw}}$, and the activation energy $U$. Our results show that hydrostatic pressure $p$ weakens the low-$T$ magnetite structure (decreases $T_{\mathrm{V}})$ and has roughly similar effects on AS in Zn-doped ${\mathrm{Fe}}_3{\mathrm{O}}_4$ and, to a much lesser extent, in stoichiometric magnetite. We have, however, found that while doping/nonstoichiometry also lowers $T_{\mathrm{V}}$, making it more prone to temperature chaos, it drastically increases the switching field, and activation and switching energies, suggesting that the trimeron order, subject to change while AS occurs, is more robust. Consequently, we conclude that the manipulation of trimerons in the process of axis switching and the mechanisms leading to the Verwey transition are distinct phenomena.

The layered oxychalcogenide semiconductor ${\mathrm{Bi}}_2{\mathrm{O}}_2\mathrm{Se}$ (BOS) hosts a multitude of unusual properties including high electron mobility. Owing to similar crystal symmetry and lattice constants, the perovskite oxide ${\mathrm{SrTiO}}_3$ (STO) has been demonstrated to be an excellent substrate for wafer-scale growth of atomically thin BOS films. However, the structural and electronic properties of the BOS/STO interface remain poorly understood. Here, through first-principles study, we reveal that polar discontinuities and interfacial contact configurations have a strong impact on the electronic properties of ideal BOS/STO interfaces. The lowest-energy [$\mathrm{Bi}\text{−}{\mathrm{TiO}}_2$] contact type, which features the contact between a ${\mathrm{Bi}}_2{\mathrm{O}}_2$ layer of BOS with the ${\mathrm{TiO}}_2$-terminated surface of STO, incurs significant interfacial charge transfer from BOS to STO, producing a BOS/STO-mixed, $n$-type metallic state at the interface. By contrast, the [Se-SrO] contact type, which is the most stable contact configuration between BOS and SrO-terminated STO substrate, has a much smaller interfacial charge transfer from STO to BOS and exhibits $p$-type electronic structure with no interfacial hybridization between BOS and STO. These results indicate that BOS grown on ${\mathrm{TiO}}_2$-terminated STO substrates could be a fruitful system for exploring emergent phenomena at the interface between an oxychalcogenide and an oxide, whereas BOS grown on SrO-terminated substrates may be more advantageous for preserving the excellent intrinsic transport properties of BOS.

Density functional theory calculations are used to systematically investigate the structural and electronic properties of $M{X}_2$ transition metal dichalcogenide monolayers with $M$ = Cr, Mo, W and $X$ = S, Se, Te that are doped with single (V, Nb, Ta) and double (Ti, Zr, Hf) acceptor dopants on the $M$ site with local $D_{3h}$ symmetry in the dilute limit. Three impurity levels that arise from intervalley scattering are found above the valence band maxima (VBM): an orbitally doubly degenerate $e^{\prime }$ level bound to the $K/K^{\prime }$ VBM and a singly degenerate $a_1^{\prime }$ level bound to the $\mathrm{\Gamma }$-point VBM. Replacing S with Se or Te lowers the $\mathrm{\Gamma }$ point VBM substantially with respect to the $K/K^{\prime }$ VBM bringing the $a_1^{\prime }$ level down with it. The relative positions of the impurity levels that determine the different structural and electronic properties of the impurities in $p$-doped $M{X}_2$ monolayers can thus be tuned by replacing S with Se or Te. Single acceptors introduce a magnetic moment of $1{\mu }_{\mathrm{B}}$ in all $M{X}_2$ monolayers. Out-of-plane magnetic anisotropy energies as large as 10 meV/dopant atom are found thereby satisfying an essential condition for long-range ferromagnetic ordering in two dimensions. For double acceptors in $M{\mathrm{S}}_2$ monolayers, both holes occupy the high-lying $a_1^{\prime }$ level with opposite spins so there is no magnetic moment; in $M{\mathrm{Se}}_2$ and $M{\mathrm{Te}}_2$ monolayers the holes occupy the $e^{\prime }$ level, a Jahn-Teller (JT) distortion wins the competition with exchange splitting resulting in the quenching of the magnetic moments. Even when the JT distortion is disallowed, magnetic double acceptors have a large in-plane magnetic anisotropy energy that is incompatible with long-range magnetic ordering in two dimensions. The magnetic moments of pairs of single acceptors exhibit long-range ferromagnetic coupling except for $M{\mathrm{S}}_2$ where the coupling is quenched for impurity pairs below a critical separation. For Se and Te compounds, the holes are accommodated in high-lying degenerate $e^{\prime }$ levels, which form triplets for all separations. However, for $X=\mathrm{Te}$, a JT distortion lifts the degeneracy of the $e^{\prime }$ levels leading to a reduction of the exchange interaction between impurity pairs. Deep, intrinsic, vacancy, and antisite defects that localize the holes might stabilize the magnetization of $p$-doped $M{X}_2$ monolayers. Our systematic study of the $p$-doped $M{X}_2$ monolayers identifies 1H ${\mathrm{CrTe}}_2$ and ${\mathrm{MoSe}}_2$ as the most promising candidates for room-temperature ferromagnetism. We combine the exchange interaction estimated from the energy difference calculated for ferromagnetically and antiferromagnetically coupled pairs with Monte Carlo calculations to estimate the Curie temperatures $T_{\mathrm{C}}$ for vanadium-doped ${\mathrm{CrTe}}_2$ and ${\mathrm{MoSe}}_2$ monolayers. Room-temperature values of $T_{\mathrm{C}}$ are predicted for V dopant concentrations of 5% and 9%, respectively. In view of the instability of ${\mathrm{CrTe}}_2$ in the 1H form, we suggest that the ${\mathrm{Cr}}_x{\mathrm{Mo}}_{1-x}{\left({\mathrm{Te}}_y{\mathrm{Se}}_{1-y}\right)}_2$ alloy system be studied. A single $d$ electron or hole is uncorrelated. However, in the single-impurity limit, the residual self-interaction of this carrier in the local spin density approximation (LSDA) can be corrected by introducing a Hubbard $U$. Doing so leads to a large increase of the ordering temperatures calculated in the LSDA (reducing the doping concentration needed to achieve room-temperature ordering) but at the expense of introducing an indeterminate parameter $U$.

In recent years, topology has offered an elegant degree of freedom (DOF) for light and sound manipulation. There exists persistent effort to explore the origin of topological phases based on symmetry, while it becomes rather challenging in complex networks or multiple DOF systems where geometric symmetries are not apparent. Here, we demonstrate a linear degeneracy induced by latent mirror symmetry in a zigzag granular chain whose DOF is three times larger than its bead number. An isospectral reduction approach and graphical representation are developed to track the topological origin of the degeneracy. We show how the latent mirror symmetry leads to the degeneracy and how it is manifested in a properly chosen eigenmode space. Moreover, we reveal the existence of topological edge states and their robustness against different disorders when the degeneracy is gapped. Our study takes a pivotal step toward exploiting topological waves in complex networks or disordered systems, opening up the perspective of offering new flexibilities for classical wave tailoring.

A simple impurity solver is shown to capture impurity-induced superconducting subgap states in quantitative agreement with the numerical renormalization group and quantum Monte Carlo simulations. The solver is based on the exact diagonalization of a single-impurity Anderson model with discretized superconducting reservoirs including only a small number of effective levels. Their energies and couplings to the impurity $d$ level are chosen so as to best reproduce the Matsubara frequency dependence of the hybridization function. We provide a number of critical benchmarks and demonstrate the solver's efficiency in combination with the reduced basis method [V. V. Baran and D. R. Nichita, Phys. Rev. B 107, 144503 (2023)] by calculating the phase diagram for an interacting three-terminal junction.

The Kitaev quantum spin liquid possesses two fractional quasiparticles, itinerant Majorana fermions and localized visons. It provides a promising platform for realizing a Majorana zero mode trapped by a vison excitation. This local mode behaves as a non-Abelian anyon capable of applications to quantum computation. However, creating, observing, and manipulating visons remain challenging even in the pristine Kitaev model. Here, we propose a theory to control visons enabled by a time-dependent local magnetic field in the Kitaev spin liquid. Examining the time evolution of the magnetic state, we demonstrate that a vison follows a locally applied field sweeping in the system. We clarify that one can move a vison accompanied by a Majorana zero mode by choosing the velocity and shape of the local field appropriately. In particular, the controllability of visons using local fields shows nonlinear behavior for its strength, which originates from interactions between Majorana fermions and visons. The present results suggest that itinerant Majorana fermions other than zero modes play a crucial role in vison transport. Our finding will offer a guideline for controlling Majorana zero modes in the Kitaev quantum spin liquid.

Recently discovered superconducting infinite-layer nickelates $R{\mathrm{NiO}}_2$ ($R$=Nd, La, Pr) attracts increasing attention as a similar system to cuprates. Both $R{\mathrm{NiO}}_2$ and YBCO cuprates display the three-dimensional (3D) CDW with wave vector $\mathit{q}\sim (2\pi /3,0,q_z)$, while $q_z$ is nonzero and incommensurate in the former system. Here, we reveal that the characteristic CDW in $R{\mathrm{NiO}}_2$ can be explained as the quantum interference between paramagnons, by focusing on the following characteristics of $R{\mathrm{NiO}}_2$: (i) prominent three dimensionality in the Fermi surface and (ii) large self-hole doping ($\sim 14\%$). This mechanism predicts the emergence of the $d_{x^2-y^2}$-wave bond order at a secondary 3D nesting vector ${\mathit{q}}^c\sim (2\pi /3,0,q_z^c)(q_z^c=0.2\pi \sim 2\pi /3)$. The obtained strong bond fluctuations lead to the non-Fermi liquid electronic states and superconducting states in nickelates.

Anyonic Fabry-Pérot and Mach-Zehnder interferometers have been proposed theoretically and implemented experimentally as tools to probe the electric charges and statistics of anyons. The experimentally observed visibility of Aharonov-Bohm oscillations is maximal at a high transmission through an interferometer but simple theoretical expressions for the electric currents and noises are only available at low visibility. We consider an alternative version of a Mach-Zehnder interferometer, in which anyons tunnel between copropagating chiral channels on the edges of quantum Hall liquids at the filling factors $n/(2n+1)$. We find simple exact solutions for any transmission at a suitably chosen ratio of the edge-channel lengths. The solutions allow a straightforward interpretation in terms of fractional charges and statistics. Our results also apply to the recently observed quantized plateaus in the fractional Chern insulator ${\mathrm{MoTe}}_2$.

The flexibility of a solid reflects its ability to accommodate reversible changes in size or shape. While the term is commonly used in describing physical and biological systems, a quantitative measure and hence the fundamental understanding of flexibility are presently lacking. Drawing on the phenomenology of flow in liquids, we introduce here a measure of intrinsic flexibility of crystalline materials as the fractional release of elastic stress or strain energy through symmetry-constrained internal structural rearrangements. This metric distinguishes robustly the concept of flexibility from that of compliance. Using first-principles density functional theory calculations, we determine the flexibility of four key systems spanning a range of elastic stiffness and underlying chemistries. We find flexibility arises not only from large structural rearrangements associated with soft phonons, but also from hard phonons that couple strongly to strain fields. Our flexibility measure enables high-throughput screening of materials databases to identify next-generation ultraflexible material.

Tight bosonic analogs of free-fermionic symmetry-protected topological phases, and their associated edge-localized excitations, have long evaded the grasp of condensed-matter and AMO physics. In this paper, building on our initial exploration [Phys. Rev. Lett. 127, 245701 (2021)], we identify a broad class of quadratic bosonic systems subject to Markovian dissipation that realize tight bosonic analogs of the Majorana and Dirac edge modes characteristic of topological superconductors and insulators, respectively. To this end, we establish a general framework for topological metastability for these systems, by leveraging pseudospectral theory as the appropriate mathematical tool for capturing the nonnormality of the Lindbladian generator. The resulting dynamical paradigm, which is characterized by both a sharp separation between transient and asymptotic dynamics and a nontrivial topological invariant, is shown to host edge-localized modes, which we dub Majorana and Dirac bosons. Generically, such modes consist of one conserved mode and a canonically conjugate generator of an approximate phase-space translation symmetry of the dynamics. The general theory is exemplified through several representative models exhibiting the full range of exotic boundary physics that topologically metastable systems can engender. In particular, we explore the extent to which Noether's theorem is violated in this dissipative setting and the way in which certain symmetries can nontrivially modify the edge modes. Notably, we also demonstrate the possibility of anomalous parity dynamics for a bosonic cat state prepared in a topologically metastable system, whereby an equal distribution between even and odd parity sectors is sustained over a long transient. For both Majorana and Dirac bosons, observable multitime signatures in the form of anomalously long-lived quantum correlations and divergent zero-frequency power spectral peaks are proposed and discussed in detail. Our results point to a paradigm for symmetry-protected topological physics in free bosons, embedded deeply in the long-lived transient regimes of metastable dynamics.

The ferromagnetically polarized gapped XXZ spin chain is studied at low temperatures. Utilizing only the one- and two-magnon spectrums and focusing on the magnon-creation contribution to the transverse dynamical susceptibility, we represent the latter in the form of the Dyson equation. Then, following the well known correspondence between the imaginary part of magnetic susceptibility and dynamical structure factor, we get the low-temperature formula for the magnon-peak lineshape. The suggested approach is effective only if the processes related to magnon creations and to transitions from magnons to coupled magnon pairs are energetically separated. As it is shown in the paper, such separation is inherent in the easy-axis chains with rather strong anisotropy. We present several plots and discuss their lineshapes. As the supplemental result we obtain integral representations for the temperature-dependent magnon resonance shift and the parameter which is usually associated with the decay rate. The low-temperature behavior of the resonance shift is studied in details. All calculations are performed up to controllable error $o\left(e^{-\beta E_{\mathrm{gap}}}\right)$.

The electrical resistivity of ${\mathrm{GdCuAs}}_2$ single crystals exhibits an anomalous Kondo-like resistivity minimum above the antiferromagnetic ordering temperature $T_{{\mathrm{N}}_1}\approx$ 10.6 K, which is unusual for a highly localized $4f$-moment (${\mathrm{Gd}}^{3+}$) system. Using x-ray resonant magnetic scattering, we determined the magnetic structure of ${\mathrm{GdCuAs}}_2$, where Gd moments are antiferromagnetically aligned along the crystallographic a axis and in the $(++--)$ arrangement in the c direction and ferromagnetically arranged in the b direction. The antiferromagnetic order appears first at q = ($\delta$, 0, 0.5) below 10 K, with an incommensurate modulation along the a axis and locks into a commensurate position at q = (1/3, 0, 0.5) below $T_{{\mathrm{N}}_2}\approx$ 6 K. Our high-resolution x-ray diffraction measurements show a two-peak structure at Q = (2, 0, 6) above the resistivity minimum, suggesting a lower-symmetry crystal structure than the reported tetragonal structure, and the Q = (2, 0, 6) peak becomes a sharp one-peak structure below the resistivity minimum, implying a magnetoelastic coupling above $T_{\mathrm{N}}$. Our findings suggest a complex interplay between the crystal structure and antiferromagnetic structure through a magnetoelastic coupling, associated with the anomalous resistivity minimum above $T_{{\mathrm{N}}_1}$.

We consider the spin-3/2 Luttinger fermions with contact attraction near the SU(4)-symmetric limit of vanishing Luttinger spin-orbit-coupling parameter responsible for band inversion, and at finite chemical potential. In the case of exact SU(4) symmetry the previously considered $s$-wave and five $d$-wave superconducting order parameters together form a six-dimensional irreducible representation which transforms as an antisymmetric tensor under SU(4). In this limit, we find the SU(4) $[\simeq \mathrm{SO}(6)$] symmetry to be spontaneously broken down to the SO(5) at the superconducting transition. When the SU(4) is reduced to the SO(3) by the weak band-inverting kinetic energy term, we show that at low temperatures the superconducting state is $is+d$, with a dominant $s$ and a small $d$ component, and spontaneously broken time-reversal symmetry. Relevance to superconductivity in doped semiconductors with diamond structure is discussed.

We recently showed that spin fluctuations of noncoplanar magnetic states can induce topological superconductivity in an adjacent normal metal [Mæland et al., Phys. Rev. Lett. 130, 156002 (2023)]. The noncolinear nature of the spins was found to be essential for this result, while the necessity of noncoplanar spins was unclear. In this paper we show that magnons in coplanar, noncolinear magnetic states can mediate topological superconductivity in a normal metal. Two models of the Dzyaloshinskii-Moriya interaction are studied to illustrate the need for a sufficiently complicated Hamiltonian describing the magnetic insulator. The Hamiltonian, in particular the specific form of the Dzyaloshinskii-Moriya interaction, affects the magnons and by extension the effective electron-electron interaction in the normal metal. Symmetry arguments are applied to complement this discussion. We solve a linearized gap equation in the case of weak-coupling superconductivity. The result is a time-reversal-symmetric topological superconductor, as confirmed by calculating the topological invariant. In analogy with magnon-mediated superconductivity from antiferromagnets, Umklapp scattering enhances the critical temperature of superconductivity for certain Fermi momenta.

An efficient method is presented to approximate the dynamics of individual polarizability tensor elements, for example, during ab initio molecular dynamics simulations. The method is based on the calculation of the quadrupole moment matrix of the position operator in the maximally localized Wannier functions representation. The presented method has a wide range of applications, particularly in vibrational spectroscopy simulations, such as (resonance) Raman, Raman optical activity, sum-frequency generation, etc. It is demonstrated that this method can lead to a several-hundred-times speedup with respect to reference linear response calculations. The predictive power of the introduced method is tested in the cases of various molecules as well as depolarized Raman spectra of gaseous and liquid methanol, in all of which remarkable agreement with the reference spectra is observed.

We obtain the numerical ground state of a one-dimensional ladder model with the upper and lower chains occupied by spatially separated electrons and holes, respectively. Under charge neutrality, we find that the excitonic bound states are always formed, i.e., no finite regime of decoupled electron and hole plasma exists at zero temperature. The system either behaves like a bosonic liquid or a bosonic crystal depending on the interchain attractive and intrachain repulsive interaction strengths. We also provide the detailed excitonic phase diagrams in the intra- and interchain interaction parameters, with and without disorder. We also comment on the corresponding two-dimensional electron-hole bilayer exciton condensation.

We present a general theory of the magnetic susceptibility of insulators that can be extended to treat spatially varying and finite frequency fields. While there are existing results in the literature for the zero-frequency response that appear to be in disagreement with each other, we show that the apparent differences between them vanish with the use of various sum rules, and that our result is in agreement with them. Although our strategy is based on the use of Wannier functions, we show that our result can be written in a “gauge-invariant” form involving Bloch functions. We can write it as the sum of terms that involve the diagonal elements of the Berry connection, and this decomposition is particularly useful in considering the limit of isolated molecules. But these contributions can be repackaged to give a form independent of those diagonal elements, which is thus generally more suitable for numerical computation. We consider a hexagonal boron nitride (h-BN) model to demonstrate the practical considerations in building a model and making calculations within this formalism.

The transport properties of hot holes in silicon at cryogenic temperatures exhibit several anomalous features, including the emergence of two distinct saturated drift velocity regimes and a nonmonotonic trend of the current noise versus electric field at microwave frequencies. Despite prior investigations, these features lack generally accepted explanations. Here, we examine the microscopic origin of these phenomena by extending a recently developed ab initio theory of high-field transport and noise in semiconductors. We find that the drift velocity anomaly may be attributed to scattering dominated by acoustic phonon emission, leading to an additional regime of drift velocity saturation at temperatures $\sim 40$ K for which the acoustic phonon occupation is negligible; while the nonmonotonic trend in the current noise arises due to the decrease in momentum relaxation time with electric field. The former conclusion is consistent with the findings of prior work, but the latter distinctly differs from previous explanations. This work highlights the use of high-field transport and noise phenomena as sensitive probes of microscopic charge transport phenomena in semiconductors.

The interfacial thermal conductance (ITC) plays a crucial role in nanoscale heat transfer, and its enhancement is of great interest for various applications. In this study, we explore the influence of resonance on the interfacial modes in pillar-based Si/Ge nanowires through nonequilibrium molecular dynamics simulations, employing both empirical and machine-learning potentials. Our results reveal a significant enhancement in the ITC by introducing pillars in the nanowire structure. The resonance-induced enhancement of the matching degree of the phonon density of states together with the calculation results of the phonon transmission coefficient indicate a significant improvement in both elastic and inelastic phonon transport at the interface. Moreover, we demonstrate the effective utilization of resonance to modulate the interfacial modes in pillar-based Si/Ge nanowires, resulting in improved phonon transport efficiency. This modulation is achieved by strategically repositioning the Si and Ge walls near the interface, leading to the development of the ATI-wall structure. Remarkably, the ATI-wall structure exhibits an unprecedented increase in the ITC compared to the original pillar-based design. To provide additional support for our conclusion, we conduct supplementary simulations using graphics processing unit molecular dynamics in conjunction with the neuroevolution potential to calculate the ITC. Our findings highlight the significance of interfacial mode modulation in enhancing the heat transfer in nanoscale systems and provide valuable insights for the design and optimization of thermal management devices and materials.