The construction of superparaelectric (SPE) systems has been demonstrated to be an essential means of enhancing energy storage properties, while the underlying physical behavior is still unclear. Here, the structure evolution of SPE was investigated on (1-$x$)($0.85{\mathrm{NaNbO}}_3-0.15{\mathrm{Sr}}_{0.7}{\mathrm{Bi}}_{0.2}{\mathrm{TiO}}_3$)-$x\mathrm{Bi}\left({\mathrm{Mg}}_{0.5}{\mathrm{Zr}}_{0.5}\right){\mathrm{O}}_3$ (NN-SBT-BMZ) ceramics by analyzing the lattice structure and electronic transitions behavior under the regulation of chemical content and temperature. The cell volume and optical band gap has been enhanced significantly, with increasing the doping contents. Moreover, the detailed phase diagram of NN-SBT-BMZ with a temperature content was derived by combining the evolution of dielectric, optical transitions, lattice structure, and phonon behavior under thermodynamic field, in which the evolution of the lattice structure is closely related to the domain structure. Noteworthy, the oscillatory processes of the main phonons near the $T_B$ temperature clearly reflect the relaxation state of the lattice structure, which is caused by the fact that the static displacements of the atoms in the crystal with respect to their equilibrium positions do not occur simultaneously. This work describes the comprehensive study of structural properties on ${\mathrm{NaNbO}}_3$-based SPE ceramics, which display positive implications for the development of energy storage capacitors.

We theoretically investigate the magnetoacoustic oscillation and the attenuation oscillation of long-wavelength acoustic phonons in nodal-line semimetals. Because of the electron-phonon interaction, we observe pronounced oscillatory behaviors in the dispersion modification and attenuation of acoustic phonons at low temperatures. These oscillations, exhibiting unique patterns associated with Fermi surface and magnetic field directions, serve as direct manifestation of both the Fermi-surface geometry and relativistic features of electrons. Our findings propose that these observed oscillations offer discernible signatures for characterizing the electronic structures of the nodal-line semimetals.

A recent experiment reported type-II multiferroicity in monolayer (ML) $\mathrm{Ni}{\mathrm{I}}_2$ based on a presumed spiral magnetic configuration (spiral-B), which is, as we found here, under debate in the ML limit. Freestanding ML $\mathrm{Ni}{\mathrm{I}}_2$ breaks its $C_3$ symmetry, as it prefers a striped antiferromagnetic order (AABB-AFM) along with an intralayer antiferroelectric (AFE) order. However, substrate confinement may preserve the $C_3$ symmetry and/or apply tensile strain to the ML. This leads to another spiral magnetic order ($\mathrm{spiral}-\mathrm{I}{\mathrm{V}}^X$), while bilayer shows a different order ($\mathrm{spiral}-{\mathrm{V}}^X$) and spiral-B dominates in thicker layers. Thus, three multiferroic phases, namely, spiral-B+FE, $\mathrm{spiral}-\mathrm{I}{\mathrm{V}}^X+\mathrm{FE}, \mathrm{spiral}-{\mathrm{V}}^X+\mathrm{FE}$, and an antimultiferroic AABB-AFM+AFE one, show layer thickness dependence and geometry-dependent dominance, ascribed to competition among thickness-dependent Kitaev, biquadratic, and Heisenberg spin-exchange interactions and single-ion magnetic anisotropy. Our theoretical results clarify the debate on the multiferroicity of ML $\mathrm{Ni}{\mathrm{I}}_2$ and shed light on the role of layer stacking induced changes in noncollinear spin-exchange interactions and magnetic anisotropy in thickness-dependent magnetism.

Oxygen vacancies are often attributed to changes in the electronic transport for perovskite oxide materials (${\mathrm{ABO}}_3$). Here, we use density functional theory coupled with nonequilibrium Green's functions to systematically investigate the influence of O vacancies and also $A$- and $B$-site vacancies, on the electronic transport as characterized by a scattering cross section. We consider ${\mathrm{SrNbO}}_3$ and $n$-type ${\mathrm{SrTiO}}_3$ and contrast results for bulk and thin film (slab) geometries. By varying the electron doping in ${\mathrm{SrTiO}}_3$ we get insight into how the electron-vacancy scattering varies for different experimental conditions. We observe a significant increase in the scattering cross section (in units of square-lattice parameter $a^2$) from $\approx 0.5\text{–}2.5a^2$ per vacancy in ${\mathrm{SrNbO}}_3$ and heavily doped ${\mathrm{SrTiO}}_3$ to more than $9a^2$ in ${\mathrm{SrTiO}}_3$ with 0.02 free carriers per unit cell. Furthermore, the scattering strength of O vacancies is enhanced in ${\mathrm{TiO}}_2$ terminated surfaces by a factor of more than 6 in lowly doped ${\mathrm{SrTiO}}_3$ compared to other locations in slabs and bulk systems. Interestingly, we also find that Sr vacancies go from being negligible scattering centers in ${\mathrm{SrNbO}}_3$ and heavily doped ${\mathrm{SrTiO}}_3$, to having a large scattering cross section in weakly doped ${\mathrm{SrTiO}}_3$. We therefore conclude that the electron-vacancy scattering in these systems is sensitive to the combination of electron concentration and vacancy location.

We explore anomalous high-harmonic generation in a model that realizes a transition from a broken time-reversal symmetry Weyl semimetal to a semi-Dirac regime, i.e., a gapless semimetal with dispersion that is parabolic in one direction and conical in the other two. We point out the intensity of the induced anomalous high harmonics is high in the semi-Dirac regime. For Weyl semimetals, we reveal anomalous high harmonics are due to excitations at momenta where the dispersion is not strictly linear and that in the linearized low-energy theory the anomalous response is harmonic only. Our findings aid in the experimental characterizations of Weyl, Dirac, and semi-Dirac semimetals.

Perovskites with Bi or Pb on the A site host a number of interesting and yet to be understood phenomena such as negative thermal expansion in ${\mathrm{BiNiO}}_3$. We employ hard x-ray photoemission spectroscopy of Ni $2p$ core level as well as valence band to probe the electronic structure of ${\mathrm{BiNiO}}_3$ and ${\mathrm{PbNiO}}_3$. The experimental results supported by theoretical calculations using dynamical mean-field theory reveal essentially identical electronic structure of the Ni–O subsystem typical of ${\mathrm{Ni}}^{2+}$ charge-transfer insulators. The two materials are distinguished by filling of the Bi(Pb)–O antibonding states in the vicinity of the Fermi level, which is responsible for the Bi disproportionation in ${\mathrm{BiNiO}}_3$ at ambient pressure and absence of similar behavior in ${\mathrm{PbNiO}}_3$. The present experiments provide evidence for this conclusion by revealing the presence/absence of Bi/Pb $6s$ states at the top of the valence band in the two materials.

The high-temperature $\delta$ phase of plutonium can be stabilized at room temperature by doping it with a few-percent gallium, and the cubic phase ${\mathrm{Pu}}_3\mathrm{Ga}$ plays a crucial role in understanding the mechanism of the stabilized $\delta$ phase of plutonium-gallium alloy. In this paper, we discovered that the spectral weights of $5f$ electrons in ${\mathrm{Pu}}_3\mathrm{Ga}$ are reduced compared to $\delta$-Pu, suggesting the increased localization of $5f$ electrons that promotes the stability of ${\mathrm{Pu}}_3\mathrm{Ga}$. Through a comprehensive investigation of the temperature-dependent correlated electronic states of ${\mathrm{Pu}}_3\mathrm{Ga}$ using a combination of the density functional theory and the embedded dynamical mean-field theory, we found that the enhanced localization of $5f$ states at high temperatures is accompanied by depressing quasiparticle resonance peaks and weakened valence fluctuations. Moreover, the quasiparticle multiplets resulting from the many-body transitions among the $5f^4, 5f^5$, and $5f^6$ electronic configurations collapse as temperature increases. The hybridizations between the $5f$ bands and conduction bands also decrease at high temperatures, causing changes in the Fermi surface geometry indicative of a temperature-driven electronic Lifshitz transition. Finally, the calculated linear specific heat coefficient $\gamma$ is approximately 112 mJ / (mol ${\mathrm{K}}^2$) at $T=80$ K, suggesting that ${\mathrm{Pu}}_3\mathrm{Ga}$ could be a promising candidate of plutonium-based heavy-fermion systems.

We have developed a microscopic many-body theory of two-dimensional coherent spectroscopy (2DCS) for a model of polarons in one-dimensional (1D) materials. Our theory accounts for contributions from all three processes: excited-state emission (ESE), ground-state bleaching (GSB), and excited-state absorption (ESA). While the ESE and GSB contributions can be accurately described using Chevy's ansatz with one-particle-hole excitation, the ESA process requires information about the many-body eigenstates involving two impurities. To calculate these double polaron states, we have extended Chevy's ansatz with one-particle-hole excitation. The validity of this ansatz was verified by comparing our results with an exact calculation using Bethe's ansatz. Our numerical results reveal that in, the weak interaction limit, the ESA contribution cancels out the total ESE and GSB contributions, resulting in less significant spectral features. However, for strong interactions, the features of the ESA contribution and the combined ESE and GSB contributions remain observable in the 2DCS spectra. These features provide valuable information about the interactions between polarons. Additionally, we have investigated the mixing time dynamics, which characterize the quantum coherences of the polaron resonances. Overall, our theory provides a comprehensive framework for understanding and interpreting the 2DCS spectra of polarons in 1D materials, shedding light on their interactions and coherent dynamics.

In this work we describe the phenomenon of Weyl-point teleportation. Weyl points usually move continuously in the configuration parameter space of a quantum system when the control parameters are varied continuously. However, there are special transition points in the control space where the continuous motion of the Weyl points is disrupted. In such transition points, an extended nodal structure (nodal line or nodal surface) emerges, serving as a wormhole for the Weyl points, allowing their teleportation in the configuration space. A characteristic side effect of the teleportation is that the motional susceptibility of the Weyl point diverges in the vicinity of the transition point, and this divergence is characterized by a universal scaling law. We exemplify these effects via a two-spin model and a Weyl Josephson circuit model. We expect that these effects generalize to many other settings, including electronic band structures of topological semimetals.

We propose a general principle for realizing second-order topological corner states in the modified Kane-Mele model with magnetization. It is demonstrated that the sign of the edge Dirac mass depends on the magnetization of the edge sublattice termination. By adjusting the directions of magnetization according to the type of sublattice at the termination of two edges, a mass domain wall can be induced in the presence of topological corner states at an arbitrary position. All previous work on introducing magnetization in the Kane-Mele model to realize second-order topological corner states can be explained by the presence of the Dirac mass domain wall with opposite signs. Applying this principle, we design square-shaped and armchair-type hexagon-shaped graphene nanoflakes with edge magnetization, allowing for the emergence of second-order topological corner states. Our findings serve as a general theory, demonstrating that the realization of second-order topological corner states is not limited by boundary type or nanoflake shape.

The quantum sun model is an interacting model that exhibits sharp signatures of ergodicity breaking phase transition. Here, we show that the model exhibits a many-body mobility edge. We provide analytical arguments for its existence, complemented by the state-of-the-art numerical simulations analyzing gap ratios, Thouless times as well as entanglement entropy of eigenstates. We also introduce the quantum sun model with particle number conservation and argue that it shares many similarities with its unrestricted predecessor.

Decades of research have revealed a deep understanding of topological quantum matter with protected edge modes. We report that even richer physics emerges when tuning between two topological phases of matter whose respective edge modes are incompatible. The frustration at the edge leads to novel boundary physics, such as symmetry-breaking phases with exotic non-Landau transitions—even when the edge is zero-dimensional. As a minimal case study, we consider spin chains with ${\mathbb{Z}}_3\times {\mathbb{Z}}_3$ symmetry, exhibiting two nontrivial symmetry-protected topological (SPT) phases. At the bulk 1+1D critical transition between these SPT phases, we find two stable 0+1D boundary phases, each spontaneously breaking one of the ${\mathbb{Z}}_3$ symmetries. Furthermore, we find that a single boundary parameter tunes a non-Landau boundary critical transition between these two phases. This constitutes a 0+1D version of an exotic phenomenon driven by charged vortex condensation known as deconfined quantum criticality. This work highlights the rich unexplored physics of criticality between nontrivial topological phases and provides insights into the burgeoning field of gapless topological phases.

We study the entanglement Hamiltonian for a spherical domain in the ground state of a nonrelativistic free-fermion gas in arbitrary dimensions. Decomposed into a set of radial entanglement Hamiltonians, we show that the entanglement spectrum in each sector is identical to that of a hopping chain in a linear potential, with the angular momentum playing the role of the subsystem boundary. Furthermore, the eigenfunctions follow from a commuting differential operator that has exactly the form predicted by conformal field theory. Rescaled by the radial Fermi velocity, this operator gives a perfect approximation of the entanglement Hamiltonian, except for large angular momenta that belong to the edge regime in the analogous gradient chain. One thus finds that the conformal field theory result becomes asymptotically exact only in one dimension.

The interplay between the spin-orbit interaction (SOI) and magnetism produces interesting phenomena in superconductors. When a two-dimensional (2D) system with a strong SOI is coupled to an $s$-wave superconductor, an in-plane magnetic field can drive the system into a gapless superconducting state and induce a mirage gap at finite energies for an Ising superconductor. In this Letter, we demonstrate that when an $s$-wave superconductor is proximitized to an altermagnet, the intrinsic anisotropic spin splitting of the altermagnet can result in a gapless superconducting state and a pair of mirage gaps at finite energy. The gapless superconductivity exhibits spin-polarized segmented Fermi surfaces, with coexisting spin-singlet and spin-triplet pairings that have a $d$-wave character. Importantly, the gapless superconducting and mirage gap features are quantified through quantum transport. Our results suggest that the altermagnet is an ideal platform for studying gapless superconducting states and mirage gap physics.

Photoelectronic devices that utilize ferroelectric polarization offer significant advantages in terms of dipole-modulated charge separation and energy band gap. In this paper, we investigate the unusual photoresponse characteristics of a two-dimensional ${\mathrm{CuInP}}_2{\mathrm{S}}_6$ crystal with cation order-disorder mediated phases, namely, paraelectricity, ferroelectricity, and dipolar glass. Notably, the photocurrent demonstrates a clear anisotropic photoresponse in the ferroelectric state, whereas it becomes isotropic with significantly reduced values in the dipolar glass state. This anisotropy-isotropy change can be attributed to ferroelectric frustration within the dipolar glass phase. In addition, the Cu cation ordering at low temperature results in a larger band gap and suppressed photocurrent compared with the paraelectric and ferroelectric phases. This discovery offers valuable insights into understanding the impact of order-disorder phase transitions on the photodetective performance of ferroelectric materials.

In this work, we investigate the localization properties of a paradigmatic model, coupled to a monitoring environment and possessing a many-body localized (MBL) phase. We focus on the postselected no-click limit with quench random rates, i.e., random gains and losses. In this limit, the system is modeled by adding an imaginary random potential, rendering non-Hermiticity in the system. Numerically, we provide evidence that the system is localized for any finite amount of disorder. To analytically understand our results, we extend the quantum random energy model (QREM) to the non-Hermitian scenario. The Hermitian QREM has been used previously as a benchmark model for MBL. The QREM exhibits a size-dependent MBL transition, where the critical value scales as $W_c\sim \sqrt{L}lnL$ with system size and presenting many-body mobility edges. We reveal that the non-Hermitian QREM with random gain-loss offers a significantly stronger form of localization, evident in the nature of the many-body mobility edges and the value for the transition, which scales as $W_c\sim {ln}^{1/2}L$ with the system size.

The hallmark of highly frustrated systems is the presence of many states close in energy to the ground state. Fluctuations between these states can preclude the emergence of any form of order and lead to the appearance of spin liquids. Even on the classical level, spin liquids are not all alike: they may have algebraic or exponential correlation decay, and various forms of long wavelength description, including vector or tensor gauge theories. Here, we introduce a classification scheme, allowing us to fit the diversity of classical spin liquids (CSLs) into a general framework as well as predict and construct new kinds. CSLs with either algebraic or exponential correlation-decay can be classified via the properties of the bottom flat band(s) in their soft-spin Hamiltonians. The classification of the former is based on the algebraic structures of gapless points in the spectra, which relate directly to the emergent generalized Gauss's laws that control the low-temperature physics. The second category of CSLs, meanwhile, are classified by the fragile topology of the gapped bottom band(s). Utilizing the classification scheme we construct new models realizing exotic CSLs, including one with anisotropic generalized Gauss's laws and charges with subdimensional mobility, one with a network of pinch-line singularities in its correlation functions and a series of fragile topological CSLs connected by zero-temperature transitions.

We explore the exchange bias coupling at the RE-RE interfaces (RE denotes rare earth) due to a plausible increase in the spin-imbalance induced by magnetic sublattice disorder around the temperature range where one of the REs exists in its conical phase while the other remains ferromagnetic (FM). In this regard, two highly textured multilayers with 29 monolayers (ML) of Ho are grown, which interface with 7 and 21 ML of Tb. For ${\mathrm{ML}}_{\mathrm{Tb}}=7$, the noncollinear spin configuration constituting a fraction of the whole stack regulates the effect of the surface-area-to-volume ratio as the helix usually remains truncated, while for ${\mathrm{ML}}_{\mathrm{Tb}}=21$, the helix can be sufficiently profound. Both samples exhibit at least two temperature-dependent phases of the spin configuration of Ho: conical and helical. For the ${\mathrm{ML}}_{\mathrm{Tb}}=7$ sample, significant exchange bias fields of up to $-0.57\pm 0.1\mathrm{kOe}$ are observed along with double hysteresis loops (DHLs) below 20 K. For ${\mathrm{ML}}_{\mathrm{Tb}}=21$, the coupling strength diminishes to $-0.055\pm 0.01\mathrm{kOe}$ as we also find shifts in the temperature behavior regimes related to the conical-to-helical and helical-to-paramagnetic phase fractions within Ho. This emblemizes the effect of helical phase formation in Tb on the Ho spin configuration. Instead of nanoclustering, regular FM behavior is seen around the temperature range of conical-to-helical phase evolution. As we replace 21 ML of Tb with 10 ML of a ferromagnet (CoFe), we find the usual DHLs and an exchange bias field up to $-0.02\pm 0.01\mathrm{kOe}$. The exchange bias phenomenon in Ho/Tb multilayer below 20 K is attributed to the small spin imbalance in the magnetic sublattice disorders in the conical phase of Ho.

The perovskite oxide heterointerface is a complex and fascinating region where charge transfer dramatically alters the coupling between charge, spin, orbital, and lattice order, resulting in novel phenomena absent in bulk materials. Understanding and controlling these interfacial effects is crucial for designing and optimizing oxide heterostructures for potential applications. Specifically, charge transfer can stabilize and enhance the ferromagnetic order at the interface, effectively improving the properties of magnetic materials. In this work, a detailed investigation of the $\mathrm{LaCo}{\mathrm{O}}_3/\mathrm{L}{\mathrm{a}}_{2/3}\mathrm{S}{\mathrm{r}}_{1/3}\mathrm{Mn}{\mathrm{O}}_3$ heterostructures revealed Mn-Co ferromagnetic coupling induced by charge transfer at the interface. Remarkably, this interfacial ferromagnetic coupling dramatically increased the Curie temperature of the $\mathrm{LaCo}{\mathrm{O}}_3$ film up to 190 K, which is significantly higher than the single $\mathrm{LaCo}{\mathrm{O}}_3$ film. Using surface-sensitive x-ray absorption spectra and x-ray magnetic circular dichroism, we find sizable $\mathrm{C}{\mathrm{o}}^{2+}$ forms from the charge transfer between Mn-Co sites at the interface. Combined with density functional theory calculations, it is clear that the $e_g{}^0\text{−}\mathrm{O}\text{−}{e}_g{}^2$ type $\mathrm{M}{\mathrm{n}}^{4+}\text{−}\mathrm{O}\text{−}\mathrm{C}{\mathrm{o}}^{2+}$ superexchange interaction is at the root of the strong ferromagnetic coupling behavior. This work demonstrates that interface modulation in perovskite heterostructures can be a powerful tool for manipulating overall magnetism. It also underscores that perovskite oxide interfaces provide an ideal platform for exploring intricate interactions between different order parameters and inducing novel interfacial effects.