We present an approach to the modeling of phase diagrams in coordinate electric fields versus temperature for model antiferroelectrics (AFE) ${\mathrm{PbZrO}}_3$ (PZO) and ${\mathrm{PbHfO}}_3$ (PHO). The essence of this method is the approximate restoration of the planar difference in the Gibbs energy $\left[\mathrm{\Delta }G\right(T,E)$] between different phases (i.e., $Pbam$, $R3c$, $R3m$, $Cm2m$) using experimental phase diagrams. This allows to recalculate $E\text{−}T$ diagrams for an arbitrary field direction. The calculated diagrams have a predictive ability, so it will be useful for future experimental works, while the analysis of the obtained thermodynamical parameters emphasizes interesting peculiarities of PZO-like AFE materials. Among them are (i) the presence of low-polarization (that may be ferrielectric) phases below and above room temperature, (ii) the presence of both a positive and negative electrocaloric effect in the different parts of the wide $E\text{−}T$ area, and (iii) the physical reason for phase boundary linearity in perovskite PZO-like materials. Since our method uses a combination of experimental data and modeling, it could serve as the bridge between experimental data and atomistic modelings, which, as we show, do not match well the experimental part so far. We are convinced that the Gibbs energy approach itself is rather general and portable on other materials (e.g., ${\mathrm{BaTiO}}_3$) and coordinates, such as pressure ($p$) and concentrations ($x$). It also can be supplemented with ferrielectric phases from current related works with the aim to solve the pending problem of the description of their energy balance.

All-solid-state nanoscale devices capable of efficiently controlling a heat flow are crucial for advanced thermal management technologies. Here we predict a magnon-driven magnetothermal resistance (mMTR) effect in multi- layers of ferromagnets and normal metals, i.e., a thermal resistance that varies when switching between parallel and antiparallel magnetization orientations of the ferromagnetic layers, even in the absence of conduction electrons in the ferromagnets. The mMTR arises from an interfacial temperature drop caused by magnon spin accumulations and can be engineered by the layer thicknesses, spin diffusion lengths, and spin conductances. The mMTR predicted here enables magnetothermal switching in insulator-based systems; we already predict large mMTR ratios up to $40\%$ for superlattices of the electrically insulating magnet yttrium iron garnet and elemental metals.

Despite its layered orthorhombic lattice structure, CuTe hosts quasi-one-dimensional (quasi-1D) charge density wave (CDW) distortions of in-plane Te chains along the $a$ axis below $T_{\mathrm{CDW}}\sim 346\mathrm{K}$. This unique quasi-1D CDW manifests itself as an in-plane resistivity anisotropy, i.e., the $a$-axis resistivity (${\rho }_a$) displays an evident humplike anomaly below $T_{\mathrm{CDW}}$ while the $b$-axis resistivity (${\rho }_b$) is featureless. Herein, we present simultaneous measurements of ${\rho }_a$ and ${\rho }_b$ at various pressures to 16.0 GPa, in order to trace the quasi-1D CDW's evolution and its interplay with the induced superconductivity (SC). We found no sign of SC at ambient pressure from ${\rho }_a$ and ${\rho }_b$ with temperatures down to as low as 0.05 K. With the application of pressure, $T_{\mathrm{CDW}}$ from ${\rho }_a$ deceases linearly yet the quasi-1D CDW character of CuTe keeps unchanged with pressures to 6.4 GPa, above which it breaks down due to the formation of an isotropic electronic interaction-driven CDW. Meanwhile, a local superconducting pairing starts to nucleate at 3.9 GPa initially within the preexisting quasi-1D CDW Te chains (along the $a$ axis) at ∼0.4 K. For a given higher pressure, distinct discrepancies in the zero-resistance temperature and the upper critical field are observed, both of which disappear suddenly along with the CDW transformation. Such a rare observation of the in-plane anisotropic SC interlocking with the quasi-1D CDW in pressurized CuTe has been discussed in terms of the particular fermiology, local superconducting pairing, and strong CDW fluctuations that are all rooted in the quasi-1D, chainlike arrangement of its in-plane Te atoms.

In recent years, organic materials have emerged as promising candidates for a variety of light-harvesting applications ranging from the infrared to the visible regions of the electromagnetic spectrum. Their enhanced excitonic binding energies and large transition dipole moments enable strong coupling with light, with some systems already reaching the ultrastrong-coupling regime. In contrast, a wide range of two-dimensional (2D) materials has been extensively explored in the literature, exhibiting high exciton stability and strong electron-hole coupling due to reduced screening effects. In this Letter, we present a microscopic model describing the interaction of 2D materials and organic molecular aggregates in an optical cavity. We predict the formation of a hybrid Wannier-Mott-Frenkel exciton polariton with an enhanced Rabi splitting, exceeding that of the pure organic cavity by several tens of meV. To elucidate this phenomenon, we examine a cavity with 2D tungsten sulfide and a cyanine dye, where this enhancement corresponds to a $5\%$ increase relative to the organic cavity. The complementary characteristics of Wannier-Mott and Frenkel excitons enable the formation of tunable polariton states that merge into a single hybrid state as a function of detuning, allowing for dual Rabi splitting mechanisms. This provides a promising platform for exploring quantum optical phenomena in both the strong- and ultrastrong-coupling regimes.

The non-Hermitian edge burst is a phenomenon observed in non-Hermitian quantum dynamics, characterized by a significant accumulation of loss at the boundaries of a system. We present an example of the edge burst effect in a lossy lattice with bipolar non-Hermitian skin effect. By introducing a weak coupling between two such non-Hermitian lattices, we demonstrate that the system exhibits bipolar scale-free localization. Through an analysis of local decay distributions and their sensitivity to system parameters, we confirm the occurrence of the edge burst effect in the system displaying scale-free localization. Our findings support the notion that the skin effect is not a necessary condition for the edge burst effect.

We present a comprehensive investigation of the structural, local structural, magnetic, and electrochemical properties of as-prepared Dy-doped Nd-based cuprate francisites [($\mathrm{C}{\mathrm{u}}_3\mathrm{Nd}{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$ (in short NdCufr)]. While studies on rare-earth (RE) francisites are well established, substitution of an $f$-block RE element (Nd) with another $f$-block RE element (Dy) represents another approach. Structural analyses reveal the compatibility of Dy doping through variations in structural parameters. Magnetic measurements show significant enhancements due to Dy doping, including sharp metamagnetic transitions and pronounced magnetic hysteresis in the 5–10 K range. The doping mechanism was further explored using local structural probes such as x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) spectroscopy. XANES and EXAFS at the $L_3$ edges of both Nd (host) and Dy (dopant) confirm the expected valence states and substitutional incorporation of Dy at the Nd sites. Notably, in this paper, we provide a report of XANES and EXAFS spectroscopy at the $L_1$ edges of Dy in francisite compounds. XANES data for the $L_1$ edges of Dy indicate weak electric quadrupole and octupole transitions alongside strong electric dipole contributions, while EXAFS results corroborate the substitutional incorporation of Dy. Additionally, the electrochemical characterization of Dy-doped NdCufr reveals a moderate supercapacitive nature. In this paper, we highlight the impact of Dy doping on the multifunctional properties of NdCufr, providing insights into their local structural and magnetic and electrochemical behavior.

This work analyzes the behavior of the interface between a ferromagnetic material and an altermagnet. We use a well-established line of arguments based on electronic mean-field calculations to show that new surface phenomena that lead to altermagnetic materials induce an exchange bias effect on the nearby ferromagnet. We reveal the physical mechanisms behind this phenomenon that lead to quantitative control over its strength. Interestingly, we predict exotic electric-field-induced phenomena. This is an analogy to the relationship between exchange bias and the injection of spin currents in spin-transfer-dominated scenarios, which has been reported earlier in the traditional antiferromagnetic/ferromagnetic junction.

Magnesium (Mg) and sulfur (S), representative elements of the $s$ and $p$ block, respectively, typically form MgS in nature, where Mg exhibits a $+2$ oxidation state and S a $-2$ oxidation state. High pressure has been shown to be an effective method for synthesizing unconventional compounds that are not stable under ambient conditions. In this paper, we propose a different stoichiometry, ${\mathrm{Mg}}_3{\mathrm{S}}_2$, with a tetragonal $P4/m$ symmetry, which stabilizes at pressures above 134 GPa, as predicted through structure prediction and first-principles calculations. The three inequivalent Mg atoms exhibit four-, six-, and eightfold coordination with sulfur, forming Mg-centered ${\mathrm{MgS}}_4$ rectangular units, ${\mathrm{MgS}}_6$ trigonal prisms, and ${\mathrm{MgS}}_8$ square prisms, respectively. This mixed coordination is a distinctive feature of high-pressure Mg-containing compounds. Further analysis reveals that ${\mathrm{Mg}}_3{\mathrm{S}}_2$ exhibits metallic properties, characterized by strong ionic bonding between Mg and S atoms. Notably, significant electronic localization is observed at the lattice vertices between two Mg atoms. Additionally, ab initio molecular dynamics simulations demonstrate that ${\mathrm{Mg}}_3{\mathrm{S}}_2$ retains its solid-state structure at high temperatures and pressures, conditions analogous to those in the Earth's mantle. These results suggest that such compounds may exist as potential constituents of the Earth's interior. These findings provide crucial insights into magnesium chemistry and contribute valuable information for refining models of the Earth's interior.

The calculation of electric polarization based on the Berry phase (BP) method plays a crucial role in understanding ferroelectric materials. However, it cannot capture local polarization within the supercell, especially in systems with complex topological structures such as flexoelectric structures and polar skyrmions. In this study, we present a method for calculating flexoelectric coefficients via graph neural networks (GNNs). We represent the polarization contribution of each unit cell to the overall supercell as the sum of the tensor contributions from each atom, while the tensor contribution from each atom can be represented as a linear combination of the local spatial components projected along the edge directions of a cluster centered on that atom. The local polarization can be obtained using GNNs without density-functional theory calculations. Using this method, we accurately calculate the flexoelectric coefficients in $\mathrm{BaTi}{\mathrm{O}}_3$ and Si, as well as the polarization distribution in the $\mathrm{PbTi}{\mathrm{O}}_3/\mathrm{SrTi}{\mathrm{O}}_3$ superlattice. Our method provides a practical approach for local contributions of electric polarization calculations in large-scale systems.

We use micromagnetic simulations to study the influence of the shape of elongated nanomagnets that vary from rectangular to elliptical shapes in an artificial spin ice array. For weakly interacting ellipselike islands, the magnetic hysteresis loops align with the Stoner-Wohlfarth model, demonstrating nearly uniform magnetization at remanence and nearly coherent rotation. As expected, nonelliptical weakly interacting islands show deviations from the model due to the curling and pinning of the magnetization at the island edge. We find that increasing interisland coupling leads to an increasingly complex magnetic reversal process due to an interplay between internal and external degrees of freedom as the shape of the islands varies. Our results open a roadmap for tailoring systems with desired magnetic properties by choosing the appropriate nanomagnet shape.

Artificial spin ices are composed of magnetic nanomagnets that are elongated to favor an average magnetization direction. The edges of the nanomagnets are less controllable and usually defined by roughness. A typical model for such nanomagnets are stadia, where the caps are semicircular. However, realistic nanomagnets could be generally in between a rectangular and an elliptical cross section and the impact of the edges on the resulting ferromagnetic resonance has not been explored. Here, we conduct micromagnetic simulations in square artificial spin ices with nanomagnets varying from a rectangular to elliptical cross sections. We show that the edge mode exhibits a significant frequency variation as a function of shape. Furthermore, the variation is particularly steep in the vicinity of a stadium shape, suggesting that experimental results can seldom be compared with numerical simulations. Our results suggest that a more precise determination of the experimentally realized nanomagnets must be done to conduct numerical experiments. In addition, we can envision that a broad distribution of shapes in an artificial spin ice can lead to a broad resonance absorption which can be relevant for electromagnetic shielding applications.

We employ the diagrammatic Monte Carlo method based on lattice path-integral representation of the particle sector and real-space diagrammatics of the phonon sector to study the effects of optical phonon dispersion on Bose-Einstein condensation of bipolarons in the bond model. For dispersionless phonons with frequency $\omega$, this model was recently shown to give rise to small-size, light-mass bipolarons that undergo a superfluid transition at high values of the $T_c/\omega$ ratio. We find that for dispersive phonons, $T_c$ remains relatively high over a broader range of the coupling strength and even keeps increasing in the deep adiabatic regime both in two and three dimensions. This result implies that phonon dispersion is not a limiting factor in the search for new materials with high superconducting temperatures.

In contrast to superconductors with weak nonmagnetic disorder, defining the superconducting state in a strongly disordered system depends on the employed figure of merit. Particularly, highly disordered superconductors reveal a substantial disparity between their local and global superconducting properties. In real materials, the disorder distribution is not fully random but exhibits spatial correlations. A pertinent question emerges regarding the influence of such correlations on superconducting characteristics on both the local and global scales. This work demonstrates that the disparity can be effectively controlled by the disorder correlations. These affect the global and local superconducting properties in a qualitatively different way, such that the difference between the critical temperatures defined by the local and global superconductivity characteristics disappears when the correlation degree exceeds a certain level.

We investigate de Gennes-Saint-James states and Josephson effect in hybrid junctions based on $d$-wave altermagnet and $d$-wave superconductor. Even though these states are associated to long junctions, we find that the $d_{x^2-y^2}$ altermagnet in a normal $\text{metal/altermagnet/}d$-wave superconductor junction forms de Gennes-Saint-James states in a short junction due to an enhanced mismatch between electron and hole wave vectors. As a result, the zero-bias conductance peak vanishes and pronounced resonance spikes emerge in the subgap conductance spectra. By contrast, the $d_{xy}$ altermagnet only features de Gennes-Saint-James states in the long junction. Moreover, the well-known features such as V-shape conductance for $d_{x^2-y^2}$ pairings and zero-biased conductance peak for $d_{xy}$ pairings are not affected by the strength of $d_{xy}$ altermagnetism in the short junction. We also study the Josephson current-phase relation $I\left(\phi \right)$ of $d$-wave $\text{superconductor/altermagnet/}d$-wave superconductor hybrids, where $\phi$ is the macroscopic phase difference between two $d$-wave superconductors. In symmetric junctions, we obtain anomalous current phase relation such as a $0\text{−}\pi$ transition by changing either the orientation or the magnitude of the altermagnetic order parameter and dominant higher Josephson harmonics. Interestingly, we find the first-order Josephson coupling in an asymmetric $d_{x^2-y^2}\text{−}\text{superconductor/altermagnet/}{d}_{xy}$-superconductor junction when the symmetry of altermagnetic order parameter is neither $d_{x^2-y^2}$ nor $d_{xy}$ wave. We present the symmetry analysis and conclude that the anomalous orientation-dependent current-phase relations are ascribed to the peculiar feature of the altermagnetic spin-splitting field.

The abundance of bulk and boundary topologies in higher-order topological phases offers remarkable tunability and diversity to boundary states but also poses a challenge to their unified topological characterization. In this work, we propose a theoretical framework to characterize time-reversal invariant topological superconductors hosting Majorana Kramers pairs (MKP) of corner states by using a series of spin Bott indices, which capture both bulk and boundary states' topology. The developed invariants can characterize MKP in arbitrarily shaped systems and all distinct spatial distribution patterns of MKP. As an illustrative example, we apply our theory to analyze the Kane-Mele model with sublattice-dependent superconducting pairing potentials. In this representative model, both intrinsic and extrinsic higher-order topological superconductors can be realized and various patterns of MKP can be engineered through edge cleavage. Despite their high sensitivity to boundary terminations, MKP can be faithfully characterized by the proposed topological invariants. We further demonstrate the characterization of higher-order topological superconductors in the BDI symmetry class using Bott indices without resolving the spin degree of freedom.

We introduce an efficient finite-element approach for large-scale real-space pseudopotential density functional theory (DFT) calculations incorporating noncollinear magnetism and spin-orbit coupling effects. The approach, implemented within the open-source DFT-FE computational framework, fills a significant gap in real-space DFT calculations using finite element basis sets, which offer several advantages over traditional DFT basis sets. In particular, we first derive the finite-element (FE) discretized governing equations involving two-component spinors, leveraging a local reformulation of DFT electrostatics. To evaluate the widely used generalized gradient approximation exchange-correlation potentials in these governing equations under the locally collinear approximation, we devise a numerical strategy that avoids the computation of ill-defined gradients of magnetization direction near zero magnetization. Additionally, we utilize an efficient self-consistent field iteration approach based on a Chebyshev filtered subspace iteration procedure exploiting the sparsity of local and nonlocal parts of FE-discretized Hamiltonian to solve the underlying nonlinear eigenvalue problem based on a two-grid strategy. Further, we propose using a generalized functional within the framework of noncollinear magnetism and spin-orbit coupling with a stationary point at the minima of the Kohn-Sham DFT energy functional to develop a unified framework for computing atomic forces and periodic unit-cell stresses. Validation against plane-wave implementations shows excellent agreement in ground-state energetics, vertical ionization potentials, magnetic anisotropy energies, band structures, and spin textures. The proposed method achieves up to 8x–11x speedups for semiperiodic and periodic systems with $\sim 5000–7000$ electrons in terms of minimum wall times compared to widely used plane-wave implementations on CPUs in addition to exhibiting significant computational advantage on GPUs for material systems with as many as 20 000 electrons. The proposed approach offers a fast, scalable, and systematically convergent framework for large-scale DFT calculations accounting for noncollinear magnetism and spin-orbit coupling, enabling more complex material simulations and extending the range of ab initio studies.

We revisit the phase diagram of the dimerized XXZ spin-$\frac{1}{2}$ chain with nearest-neighbor couplings which was studied numerically by Mondal et al. [Phys. Rev. B 106, L201106 (2022)]. The model has isotropic $XY$ couplings which have a uniform value and $ZZ$ couplings which have a dimerized form, with strengths $J_a$ and $J_b$ on alternate bonds. We find a rich phase diagram in the region of positive $J_a,J_b$. We provide a detailed understanding of the different phases and associated quantum phase transitions using a combination of mean-field theory, low-energy effective Hamiltonians, renormalization group calculations employing the technique of bosonization, and numerical calculations using the density-matrix renormalization group (DMRG) method. The phase diagram consists of two Ising paramagnetic phases called ${\mathrm{IPM}}_0$ and ${\mathrm{IPM}}_{\pi }$, and a phase with Ising Neel (IN) order; all these phases are gapped. The phases ${\mathrm{IPM}}_0$ and ${\mathrm{IPM}}_{\pi }$ are separated by a gapless phase transition line $0\le J_a=J_b\le 1$—the well-known Tomonaga Luttinger liquid captured by a conformal field theory (CFT) with central charge $c=1$. In contrast, there are two phase transition lines separating ${\mathrm{IPM}}_0$ or the ${\mathrm{IPM}}_{\pi }$ from IN that are described by $c=\frac{1}{2}$ CFTs and correspond to quantum Ising transitions. In fact, the $c=1$ line bifurcates into the two $c=\frac{1}{2}$ lines at the point $J_a=J_b=1$; the shape of the bifurcation is found analytically using RG calculations. A symmetry analysis shows that ${\mathrm{IPM}}_0$ is a topologically trivial phase while ${\mathrm{IPM}}_{\pi }$ is a time-reversal symmetry-protected topological phase (SPT) with spin-$\frac{1}{2}$ states at the two ends of an open system. A gap opens in the low-energy spectrum whenever one moves away from one of the phase transition lines; the scaling of the gap with the distance from a transition line is found analytically using the RG method. The numerical results obtained by the DMRG method are in good agreement with the analytical results. Further, we show that useful insights into the nature of the phase diagram of the above Hamiltonian, particularly the SPT as well as the phase transitions, is obtained via Kramers-Wannier duality to a deformed quantum Ashkin-Teller model. Finally, we propose experimental platforms for testing our results.