We investigate the topological properties of hardcore bosons possessing nearest-neighbor repulsive interactions on a two-leg ladder. We show that by allowing nearest-neighbor dimerized interactions instead of hopping dimerization, the system exhibits topological phases and phase transitions under proper conditions. First, by assuming uniform hopping throughout the ladder, we show that when interaction along the legs are dimerized and the dimerization pattern is different in the legs, a trivial rung-Mott insulator to a topological bond order phase transition occurs as a function of the dimerization strength. However, for a fixed dimerization strength, the system exhibits a topological to trivial phase transition with increase in the rung hopping. A completely different scenario appears when the rung interaction is turned on. We obtain that for a ladder with uniform hopping, the repulsive interaction either turns the topological phase into a trivial rung-Mott insulator or a charge density wave phase. Such topological features are absent when the dimerization pattern in the nearest-neighbor interaction is considered to be identical in both the legs of the ladder. We numerically obtain the ground-state properties and also show the signatures of topological phase transitions through Thouless charge pumping.

Nonlinear spintronics, which combines nonlinear dynamics with spintronics, opens a new route for controlling spin and spin dynamics beyond conventional spintronics based on linear responses. Electron correlations can lead to a large nonlinear response and thus may play a key role in nonlinear spintronics. This paper focuses on the nonlinear Edelstein effect (NEE) and examines the impact of electron correlations on the NEE through numerical calculations on a Hubbard model. We find that electron correlations can either enhance or suppress the nonlinear response. Specifically, the enhancement and suppression are due to the real and imaginary components of self-energy, respectively. In addition, the NEE is closely related to photomagnetic and optomagnetic effects. Our findings demonstrate that electron correlations can either enhance or suppress the optical spin injection, depending on light frequencies, whereas always strengthening the inverse Faraday effect.

Computing the temperature and stress dependence of the elastic constants from first principles in noncubic materials remains a challenging problem. Here, we circumvent the aforementioned challenge via the generalized quasiharmonic approximation (gQHA) with the irreducible derivative approach for computing strain-dependent phonons using finite difference, explicitly including dipole-quadrupole contributions. We showcase the gQHA in ferroelectric ${\mathrm{PbTiO}}_3$, computing all elastic constants and piezoelectric strain coefficients at finite temperature and stress. The gQHA overestimates the temperature dependence of the lattice parameters and elastic constant tensor, demonstrating the need for an explicit treatment of lattice anharmonicity as a function of strain.

The interplay of spin and motional degrees of freedom forms a key element in explaining stripe formation accompanied by sublattice reversal of local antiferromagnetic ordering in interacting fermionic models. A long-standing question aims to relate pairing to stripe formation, intending to discern the applicability of simple models that observe this phenomenon in understanding cuprate physics. By departing from fermionic statistics, we show that the formation of stripes is rather generic, allowing one to unveil its competition with superfluid behavior. To that end, we use a combination of numerical methods to solve a model of interacting hardcore bosons in ladder geometries, finding that once stripes are formed, either via external pinning or spontaneously, a sublattice reversal ($\pi$-phase shift) of charge ordering occurs, suppressing the superfluid weight. Lastly, we show that when the Cooper pairs are not local, as in the attractive Hubbard model with finite interactions, auxiliary-field quantum Monte Carlo calculations show evidence of fluctuating stripes, but these are seen to coexist with superfluidity. Our results corroborate the picture that static stripes cannot be reconciled with pairing, unlike the case of fluctuating ones.

Within first-principles calculations, we explore superconductivity in Ca-intercalated bilayer silicene compound, ${\mathrm{Si}}_2{\mathrm{CaSi}}_2$. This arises from the coupling of interlayer flowerlike $\mathrm{\Gamma }$-centered Fermi surface formed by the hybridization of Ca-3$d$ and Si-3$p_z$ orbitals with low-energy out-of-plane vibrations enabled by silicene's buckling. The consequent large electron-phonon coupling, as evident from the Eliashberg spectral function, leads to superconductivity below 12.5 K in this two-dimensional covalent system. Our results reveal the key control parameters to achieve superconductivity in experimentally synthesizable silicon-based thin materials that can find diverse applications.

Negative capacitance can enable ultralow-power field effect transistors, though the concept of ferroelectric negative capacitance, especially its stability, remains contentious. We resolve this issue here by analyzing ferroelectric/dielectric heterostructure rigorously using the Landau-Denvonshire theory, identifying three critical dielectric thicknesses upon which the stability of negative capacitance changes. A critical electric window is also identified, beyond which stable negative capacitance cannot be maintained. Between the first and second critical thicknesses, metastable negative capacitance exists, yet it will be lost and cannot be recovered once the electric window is broken. Between the second and third critical thicknesses, negative capacitance is always stable within the electric window, resulting in hysteretic double P-E loop. Beyond the third critical thickness, P-E loop becomes hysteresis free. Singularities in the effective dielectric constant are also observed at the critical thickness or electric field.

Spin-reorientation (SR) phase transition (PT), spin reversals, hysteresis, and thermal phenomena in neodymium orthoferrite are studied within the framework of the previously presented model of the magnetic properties of orthoferrites [Phys. Rev. B 107, 224407 (2023)]. A rigorous proof of an appearance of the SR second-order PT at temperature $T_{\mathrm{SR}}$ in infinitesimal magnetic field along one of the crystal symmetry axes is given. It is done without introduction of high-order anisotropy constants used in traditional phenomenological theories for the orthoferrite thermodynamics. The expression for temperature $T_{\mathrm{SR}}$ considers a complex competition of existing anisotropies. Unfortunately, due to the displacement of domain boundaries, this temperature is quite difficult to determine. Since the anisotropy at temperature $T_{\mathrm{SR}}$ is predicted to disappear, a method for $T_{\mathrm{SR}}$ determination is proposed. Particular attention is paid to the study of an influence of demagnetizing field on the structure of phase diagrams as well as to the analysis of the experimental data on temperature and field dependence of the magnetization. It has been established that the specimen shape essentially influences temperature dependences of the PT critical fields. Using the experimental temperature dependence of the spin-reversal critical fields, the microscopic anisotropic interaction parameters in neodymium orthoferrite are determined, on the basis of which the magnetization, spin-reversal energies, specific heat capacity, and hysteresis loops are calculated. The results of the experiment and theory are in good agreement.

The spin reversal in dilute ${\mathrm{Li}}_2({\mathrm{Li}}_{1-x}{\mathrm{Fe}}_x)\mathrm{N}$ with $x<1\%$ is dominated by resonant quantum tunneling of spatially separated spins. We report on the effect of finite couplings between those states that give rise to cooperative, simultaneous quantum tunneling of two spins. This phenomenon, known as spin-spin cross relaxation, effectively elucidates the fine structure observed in isothermal magnetization loops, a previously unresolved aspect. Temperature- and field-dependent magnetization measurements were conducted over a range from $T=0.23$ to 300 K in applied fields of up to ${\mu }_{0}H=7.5\mathrm{T}$. The effect of transverse fields is investigated and magnetic dipole fields are computed numerically. Our findings affirm the importance of magnetic interactions in dilute ${\mathrm{Li}}_2({\mathrm{Li}}_{1-x}{\mathrm{Fe}}_x)\mathrm{N}$ and underscore its exemplary suitability as a model system for investigating spin-reversal processes at the microscopic level. This is attributed to its comparatively simple crystal structure, the availability of large single crystals, elevated characteristic energies, and well-defined energy levels.

We study the amplitude and phase fluctuations of the Ginzburg-Landau quasiorder parameter for superconductors in two spatial dimensions. Starting from the mean-field critical temperature $T_{\mathrm{c}0}$, we calculate the beyond-mean-field critical temperature $T_{\mathrm{c}}$ by including thermal fluctuations of the quasiorder parameter within the Gaussian level. Moreover, from our beyond-mean-field results, we derive the Berezinskii-Kosterlitz-Thouless critical temperature $T_{\mathrm{BKT}}$, which takes into account topological vortex-antivortex excitations in the phase fluctuations as well as the amplitude fluctuations, to obtain the shifts of transition temperatures. We elucidate how the Gaussian thermal fluctuations and phase fluctuations associated with vortex excitations affect thermodynamic properties by determining the $H\text{−}T$ phase diagram for a type-II superconductor and computing the critical behaviors of the heat capacity, which are experimentally accessible, allowing the characterization of the cascade of different kinds of fluctuations in 2D superconductors.

We investigate the electronic structure and superconducting gaps in the charge density wave (CDW) states of kagome superconductors, focusing on the concurrent presence of CDW and superconducting orders. Two predominant CDW configurations are explored, the trihexagonal (TrH) and star-of-David (SoD) patterns, involving charge bond order (CBO) and chiral flux phase (CFP), corresponding to real and imaginary bond orders. In the isotropic $s$-wave superconducting state, the presence of CBO alone maintains an isotropic superconducting gap, whereas the introduction of CFP induces anisotropy in the gap, manifesting time-reversal symmetry breaking due to the CFP. Our analysis extends to the topological properties of these states, revealing a marked topological phase transition in the TrH configuration from a trivial to a nontrivial state with increasing CFP intensity. This transition suggests that the introduction of CFP could catalyze the emergence of topological superconductivity, potentially leading to the presence of Majorana excitations. The results contribute significantly to understanding the complex interplay between various CDW patterns and superconductivity in kagome superconductors. They provide a theoretical framework for the diverse experimental observations of energy gaps and open different avenues for research into topological superconductivity and its potential applications. This paper underscores the necessity for further experimental and theoretical exploration to unveil additional intertwined quantum states and functionalities in these intriguing materials.

Detecting Majorana zero modes (MZMs) in topological superconductors remains challenging, as localized nontopological states can mimic MZM signatures. Here, we propose electron interferometry by nonlocal transport measurements as a definitive probe to distinguish MZMs from nontopological states. We develop an analytical minimal model showing that interference of electrons passing through two MZMs in parallel exhibits a robust pattern, in contrast to a nontopological system. We then numerically confirm this using various topological superconductor models. We find that MZMs are characterized by an interference pattern that is insensitive to various perturbations, such as electrostatic gate potential, and resilient to disorder. Our proposed interferometry approach offers an experimentally accessible means to detect MZMs, probing their underlying nature through a universal response.

The atomic motion in molecular crystals, such as high-pressure hydrogen or hybrid organic-inorganic perovskites, is very complex due to quantum anharmonic effects. In addition, these materials accommodate rotational degrees of freedom. All the approximate methods that describe the nuclei thermodynamics using Cartesian coordinates lead to an unphysical hybridization of roto-librations with other high-energy modes. Hence, they do not accurately account for the free energy contributions of these degrees of freedom. So, a reliable description of a molecular crystal's phase diagram is only possible with Path Integral Molecular Dynamics (PIMD) at a high computational cost. This work shows how to include roto-librational modes in the Self-Consistent Harmonic Approximation (SCHA) framework. SCHA approximates the nuclei Cartesian fluctuations to be Gaussian, thus neglecting curvilinear motion. Keeping its low computational cost, we employ the generalization of SCHA, called nonlinear SCHA (NLSCHA). Our method relies on a Gaussian ansatz for the nuclei density matrix on a curved manifold, allowing us to map roto-librations into harmonic modes defined on a surface. By optimizing the surface's curvature variationally, we minimize the free energy, allowing the spontaneous activation of these degrees of freedom without external parameters. Notably, in the limit of vanishing curvature, we recover the standard SCHA.

Perpendicular magnetic anisotropy (PMA) has emerged as a key focus in spintronics due to its inherent stability against thermal fluctuations, scalability, endurance, and low switching current density, causing an ongoing search for new ways to control PMA. In this study, we predict an in-plane to out-of-plane transition in magnetic anisotropy orientation in the two-dimensional (2D) multiferroic material ${\mathrm{CuCrP}}_2{\mathrm{S}}_6$ (CCPS) upon isovalent doping with indium, based on first-principles calculations. The transition is triggered by a quasilinear increase in magnetocrystalline anisotropy (MCA) energy with In concentration in the mixed ${\mathrm{CuCr}}_{1-x}{\mathrm{In}}_x{\mathrm{P}}_2{\mathrm{S}}_6$ layer. Our calculations show that this increase in MCA energy results from two distinct and equally important contributions. The first contribution is purely structural in nature. It is the effect of a biaxial tensile strain acting on the CCPS units of the film caused by the increased in-plane lattice parameter upon the addition of In. The second contribution is a “chemical effect” due to the chemical substitutions at fixed geometry. We find it to be related to the decrease in the near-valence-edge density of states of the in-plane majority-spin $d$ orbitals of Cr atoms through hybridization changes produced by isovalent doping with a nonmagnetic element. Based on the analysis of the underlying mechanisms, we extend our findings relative to the tuning of MCA energy towards more positive values to other nonmagnetic dopants, isovalent with ${\mathrm{Cr}}^{3+}$ and of ionic radius larger than that of ${\mathrm{Cr}}^{3+}$ in 2D CCPS and related metal thiophosphates.

Superconductor/ferromagnet/superconductor Josephson junctions are paradigmatic systems for studying the delicate interplay of superconductivity and magnetism via proximity effects as well as their composite excitations. Here, we analyze the collective modes (CM) in such a heterostructure by taking into account the interplay between the demagnetization field $H_{\mathrm{dem}}$ and the field caused by the anisotropy of the ferromagnet $H_{\mathrm{an}}$, which was previously neglected. It turns out that the spectrum of composite collective modes, $\omega \left(k\right)$, has a qualitatively different form in the case of $H_{\mathrm{dem}}<H_{\mathrm{an}}$ and of $H_{\mathrm{dem}}>H_{\mathrm{an}}$. In the first case, the dependence $\omega \left(k\right)$ has the same form as in previous studies, whereas in the second case, the spectrum looks completely different. In particular, for moderate or weak anisotropy in ferromagnet, the group velocity of collective modes demonstrates inflection point where the group velocity becomes infinite and is superluminal. Furthermore, this point separates purely real and complex-conjugate solutions for the collective modes and is also an exception point. We show that the difference of the CMs spectra can be revealed by the Fiske experiment, i.e., by measuring the $I\text{−}V$ characteristics in the presence of magnetic field and voltage.

Metastable states of quantum many-body systems with confinement offer a means to simulate false vacuum phenomenology, including nonequilibrium dynamical processes like decay by nucleation, in truncated limits. Recent work has examined the decay process in one-dimensional (1D) ferromagnetic Ising spins and superfluids. In this paper, we study nucleation dynamics in 1D antiferromagnetic neutral atom chains with Rydberg interactions, using both numerical simulations and analytic modeling. We apply a staggered local detuning field to generate the metastable and ground states. Our efforts focus on two dynamical regimes: decay and annealing. In the first, we corroborate the phenomenological decay rate scaling and determine the associated parameter range for the decay process; in the second, we uncover and elucidate a procedure to anneal the metastable state from the initial to the final system, with intermediate nucleation events. We further propose experimental protocols to prepare the required states and perform quenches on near-term neutral atom quantum simulators, examining the experimental feasibility of our proposed setup and parameter regime.

A junction of two 2/3 fractional quantum Hall (FQH) edges, with no charge tunneling between them, may exhibit Anderson localization of neutral modes. Manifestations of such localization in transport properties of the junction are explored. There are two competing localization channels, “neutral-mode superconductivity” and “neutral-mode backscattering.” Localization in any of these channels leads to an effective theory of the junction that is characteristic for FQH effect of bosons, with a minimal integer excitation charge equal to 2, and with elementary quasiparticle charge equal to 2/3. These values can be measured by studying shot noise in tunneling experiments. Under the assumption of ballistic transport in the arms connecting the junction to contacts, the two-terminal conductance of the junction is found to be 4/3 for the former localization channel and 1/3 for the latter. The four-terminal conductance matrix reveals in this regime a strong quantized drag between the edges induced by neutral-mode localization. The two localization channels lead to opposite signs of the drag conductance, equal to $\pm 1/4$, which can also be interpreted as a special type of Andreev scattering. Coherent random tunneling in arms of the device (which are segments of 2/3 edges) leads to strong mesoscopic fluctuations of the conductance matrix. In the case of fully equilibrated arms, transport via the junction is insensitive to neutral-mode localization: The two-terminal conductance is quantized to 2/3 and the drag is absent.

Kondo metals with geometric frustration offer fertile ground for exploring exotic states of matter with a field-induced fractional magnetization platform and nonsaturating magnetoresistance. Herein, a ${\mathrm{Ce}}_3{\mathrm{ScBi}}_5$ single crystal with anti-${\mathrm{Hf}}_5{\mathrm{Sn}}_3\mathrm{Cu}$ hexagonal structure was successfully synthesized via the bismuth self-flux method, leading to the formation of cerium cations arranged in a frustrated structure within a distorted kagome lattice. Magnetic measurements exhibit two distinct antiferromagnetic transitions at 4.1 and 5.9 K. Specifically, the occurrence of multiple metamagnetic transitions between magnetization plateaus is evidenced upon applying magnetic fields perpendicular to the $c$ axis. Transport measurements highlight remarkable Kondo-lattice characteristics and anisotropic magnetoresistance in ${\mathrm{Ce}}_3{\mathrm{ScBi}}_5$. The anomalous Hall contributions are observed at low temperatures under critical fields, suggesting Fermi surface reconstruction in a subset of the metamagnetic transitions. We have constructed a temperature-field phase diagram to provide comprehensive information on the complex magnetic structures arising from competitive interactions. Our work establishes ${\mathrm{Ce}}_3{\mathrm{ScBi}}_5$ and related materials as a unique platform for exploring low-dimensional quantum fluctuations in bulk crystals, and analyzes the critical role of geometric frustration in Kondo and Ruderman-Kittel-Kasuya-Yosida physical frameworks.