We measured the complex Young modulus of ${\mathrm{BaTiO}}_{3-\delta }$ (BT), ${\mathrm{Ba}}_x{\mathrm{Sr}}_{1-x}{\mathrm{TiO}}_{3-\delta }$ (BST), and $\left({\mathrm{Ba}}_{0.85}{\mathrm{Ca}}_{0.15}\right)\left({\mathrm{Zr}}_{0.1}{\mathrm{Ti}}_{0.9}\right){\mathrm{O}}_{3-\delta }$ (BCTZ) during heating and cooling runs at various O deficiencies [which dope electrons rendering the samples semiconducting/conducting ferroelectrics (FEs)] and aging times. The elastic energy loss has peaks due to the jumps of isolated O vacancies (${\mathrm{V}}_{\text{O}}$'s) and reorientations of pairs of ${\mathrm{V}}_{\text{O}}$'s in the paraelectric phase, from which the respective rates and activation energies are measured. These rates control the mechanisms of domain clamping, pinning, fatigue, and anything related to the ${\mathrm{V}}_{\text{O}}$ mobility. In the FE phase, the drop of the losses due to the domain wall (DW) motion upon introduction of ${\mathrm{V}}_{\text{O}}$'s monitors the degree of pinning. In addition, large shifts of $T_{\text{C}}$ are observed at the same value of $\delta$ upon varying the permanence time in the FE state, up to $\mathrm{\Delta }{T}_{\text{C}}=$ 21 K in BST, while no aging effect is found in BCTZ. The phenomenology is explained by considering that $T_{\text{C}}$ is depressed mainly by the mobile electrons doped by ${\mathrm{V}}_{\text{O}}$'s. Each isolated ${\mathrm{V}}_{\text{O}}$ dopes two electrons as itinerant ${\mathrm{Ti}}^{3+}$ ions, but when it forms a stable linear ${\mathrm{V}}_{\text{O}}$–${\mathrm{Ti}}^{2+}$–${\mathrm{V}}_{\text{O}}$ pair, the two electrons of the ${\mathrm{Ti}}^{2+}$ are subtracted from the mobile ones, halving doping. The rise of $T_{\text{C}}$ during the initial aging is then explained in terms of the progressive aggregation of the ${\mathrm{V}}_{\text{O}}$'s. Prolonging aging for years leads to a decrease of $T_{\text{C}}$, explained assuming that the most stable position of ${\mathrm{V}}_{\text{O}}$ is at ${90}^{\circ }$ DWs, whose geometry is incompatible with the pairs. Then after enough time, the ${\mathrm{V}}_{\text{O}}$ initially aggregated within the domains dissociate to decorate the ${90}^{\circ }$ walls, increasing doping and lowering $T_{\text{C}}.$ The absence of such effects in BCTZ is due to larger activation energy for pair reorientation and pair binding energy. Then at room temperature, practically all ${\mathrm{V}}_{\text{O}}$'s are paired and static over a timescale of hundreds of years, explaining the superior resistance of BCTZ to fatigue.

In this paper, we explore the inverse design of ultrawideband spatial filters by temporal profiles. As opposed to previous works, here we employ a complete nonlinear inversion scheme, which leads to flexibility in the design and to practically reasonable profiles. We express the forward problem using the temporal local impedance and temporal reflection coefficient, akin to those used in the theory of time-harmonic and spatially inhomogeneous transmission lines. For the inversion, we use a straightforward gradient-descent scheme that is applied to a loss function calculated in terms of the temporal reflection coefficient. This calculation yields a piecewise discontinuous temporal profile of the required filter. We further demonstrate, using finite-difference-time-domain simulations, the applicability of the piecewise discontinuous design also for practical soft (gradual) temporal transitions. For the sake of simplification, we assume that the time-dependent medium is instantaneous (i.e., dispersion effects are neglected) and that the temporal transitions can be implemented synchronously over the entire transmission-line structure. While these assumptions are obviously restricting in the general case, structures respecting these constraints have been experimentally demonstrated in radio frequencies using slow-wave metamaterial transmission-line configurations. Since the approach is formulated in terms of transmission-line quantities, it is applicable not only in electromagnetics but also in acoustics.

The kagome intermetallic compound $R{\mathrm{V}}_6\mathrm{S}{\mathrm{n}}_6$ ($R=\mathrm{rare}$ earth) not only supports unique lattice geometries and nontrivial topological band structures but also exhibits long-range magnetic order at low temperatures, providing an ideal platform for studying interactions among electrons, phonons, and magnetism. Phonons play a crucial role in the coupling between magnetic order and topological fermions, whose dynamics are essential for understanding the complex multiple degrees of freedom interaction in $R{\mathrm{V}}_6\mathrm{S}{\mathrm{n}}_6$. In this work we systematically investigate the temperature-dependent coherent phonon dynamics of $\mathrm{Gd}{\mathrm{V}}_6\mathrm{S}{\mathrm{n}}_6$, and two characteristic temperature points have been identified (i.e., $T_{\mathrm{e}}$ at $\sim 100\mathrm{K}$ and $T_{\mathrm{m}}$ at $\sim 5\mathrm{K}$). Specifically, we have observed the anomalous softening and suppressed decaying of the $\mathrm{A}{{}_{\mathrm{g}}}^4$ phonon mode when approaching $T_{\mathrm{e}}$, which may result from the change of density of states near the Fermi surface, while around $T_{\mathrm{m}}$, the hardening and accelerated decaying of the $\mathrm{A}{{}_{\mathrm{g}}}^4$ phonon mode emerges since the buildup of magnetic order alters the phonon energy renormalization and opens an additional scattering channel.

Based on the nonequilibrium Green's function theory, we derived the spinor Boltzmann equation for the skyrmionium in the ferromagnetic layer of a heavy metal/ferromagnet bilayer structure, where a Rashba spin-orbit coupling arises from the structural asymmetry. Notably, the spatially varying magnetic texture introduces a forcelike term into the transport equation. By integrating over the momentum in the spinor Boltzmann equation, we obtained the charge continuity equation and the spin diffusion equation. From the spin diffusion equation, the spin torque was derived, including both spin-transfer torque and spin-orbit torque, Numerical calculations of spin accumulation and spin current were performed, and the spin accumulation distribution within the skyrmionium was visualized. Finally, using the Landau-Lifshitz-Gilbert-Levy equation and a linear stability analysis method, the critical electric field for the skyrmionium was determined.

Experimental and numerical spectroscopy have revealed rich physics in antiferromagnets, in particular in frustrated and doped systems. The Majumdar-Ghosh (MG) model has an analytically known spin-disordered ground state of dimerized singlets as a result of magnetic frustration. Here we study the single-hole angle-resolved photoemission spectrum (ARPES) of a doped MG model, where we introduce a spin-hole interaction that is experimentally accessible with ultracold molecules. We report a bound spinon-holon ground state and clear signatures of a spinon-holon molecule state and polarons in the ARPES spectrum at different magnetizations. Moreover, we find signatures of an emergent Feshbach resonance with tunable interactions associated with the unbinding of the spinon and the holon. Our results provide new insights into the physics of dopants in frustrated $t\text{−}J$ models and establish the latter as a new platform for studies of emergent few-body phenomena.

The discovery of unconventional superconductivity around 80 K in perovskite nickelates under high pressure has furnished a new platform to explore high-temperature unconventional superconductivity in addition to cuprates. Understanding the normal state of nickelate superconductors is crucial to uncovering the origin of this unconventional superconductivity and gaining further insight into its underlying mechanism. In this paper, we systemically study the transport properties of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ by tuning the pressure under high magnetic fields. Magnetoresistance (MR) consistently exhibits a quasiquadratic dependence on the magnetic field across all measured pressures and temperatures. Increased pressure enhances the metallicity of the system and leads to a monotonic increase in MR, which follows the extended Kohler's rule. These results suggest the normal state of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ to be of a multiband metallic nature.

We employ a systematic approach to construct superconducting order parameters based on the spin space group. Compared to magnetic space groups where spatial and spin rotation of elements are completely locked, the superconducting channels and the forms of basis functions in spin space groups can be different. Furthermore, we utilize the obtained basis functions to construct the Ginzburg-Landau free energy and discuss the possible superconducting ground states as well as the interplay between superconducting states and magnetic orders. By virtue of those results, we discuss the application of our theory to realistic systems. Our work provides a rigorous description of superconducting gap functions in the case of spin space group and enables further study of the interplay between superconductivity and magnetism.

Stress plays a crucial role in thin films and layered systems, and thus significantly influences the material's electrical, mechanical and (nonlinear) optical responses. Despite lithium niobate's wide applicability as a nonlinear optical material, the impact of mechanical stress on its nonlinear optical properties is not well characterized. In this work, we systematically study both experimentally and theoretically, the nonlinear optical responses of thin film lithium niobate (TFLN) single crystals. Compressive and tensile stress is applied in our experiment using a piezodriven strain cell. We then record the second-harmonic-generated (SHG) response in back-reflection geometry, and compare these results to theoretical modeling using density functional theory (DFT). Both methods consistently reveal that uniaxial stress induces changes of the nonlinear optical susceptibility of certain tensor elements on the order of up to 1 pm/(V GPa). The exact value depends on the tensor element that is addressed in our SHG analysis, on the crystal orientation, and also whether using compressive or tensile stresses. Furthermore, a lowering of the crystal symmetry when applying stress along the $x$ or $y$ crystallographic axes is observed by the appearance of new nonlinear optical tensor elements within the strained crystals.

As an important effect induced by the particle-lattice interaction, the Peierls transition, a hot topic in condensed matter physics, is usually believed to occur in one-dimensional fermionic systems. We here study a bosonic version of the one-dimensional Ising-Kondo lattice model, which describes two-species itinerant bosons, essentially acting as pseudospins, interacting with the localized magnetic moments via only longitudinal Kondo exchange. We show that, by means of perturbation analysis and numerical density-matrix renormalization group method, a bosonic analog of the Peierls state can occur in proper parameter regimes. The Peierls state here is characterized by the formation of a long-range spin-density-wave order, the periodicity of which is set by the density of the itinerant bosons. The ground-state phase diagram is mapped out by extrapolating the finite-size results to the thermodynamic limit. Apart from the bosonic Peierls state, we also reveal the presence of some other magnetic orders, including a paramagnetic phase and a ferromagnetic phase. We finally propose a possible experimental scheme with ultracold atoms in optical lattices. Our results broaden the frontiers of current understanding of the one-dimensional particle-lattice interaction system.

We develop a mesoscale transport theory for the charge and spin degrees of freedom of itinerant carriers in a $d$-wave altermagnet. Our effective Lagrangian description is built on the slave-boson formulation of the microscopic $t-J$ model. We obtain a spin-polarized diffusive contribution to the effective Hamiltonian, which has no counterpart in conventional antiferromagnetism and is parametrized by the spin splitting, responsible for the so-called spin-splitter effect in $d$-wave altermagnets. We also elucidate the spin-transfer response of the itinerant fluid as well as the spin pumping into the altermagnet, which exhibit previously unidentified combinations of the charge current and spatial partial derivatives (namely, {$j_x^e,{\partial }_y$} and {$j_y^e,{\partial }_x$}). The emergent spin-transfer physics in $d$-wave altermagnets opens up promising perspectives for the dynamics of spin textures, such as the domain-wall motion driven by transverse charge currents. Additionally, we consider the effect of elastic distortions on the aforementioned transport properties.

Low-energy spin dynamics is investigated by ${}^{35}\mathrm{Cl}$ NMR measurements in a frustrated antiferromagnet ${\mathrm{Ca}}_3{\mathrm{ReO}}_5{\mathrm{Cl}}_2$. The local spin susceptibility measured with the Knight shift behaves as a one-dimensional Heisenberg antiferromagnet and remains constant down to low temperatures, as expected in a gapless Tomonaga-Luttinger liquid. The nuclear spin-lattice relaxation rate $T_1^{-1}$ demonstrates a slowing down of atomic motions and a power-law evolution of spin correlation. The Luttinger parameter is enhanced in a site-selective manner depending on the form factor of dynamical spin susceptibility. The strong anisotropy of $T_1^{-1}$ reflects the strong spin-orbit coupling through Dzyaloshinskii-Moriya interaction. The ground state exhibits an incommensurate antiferromagnetic ordering with low-lying magnon excitations.

The semimetallic behavior of the perovskite iridate ${\mathrm{SrIrO}}_3$ shifts the end member of the strongly spin-orbit (SO) coupled Ruddlesden-Popper series ${\mathrm{Sr}}_{n+1}{\mathrm{Ir}}_n{\mathrm{O}}_{3n+1}$ away from the Mott insulating regime and the half-filled pseudospin $J_{\mathrm{eff}}=\frac{1}{2}$ ground state well established in the layered iridates ($n=1$ and 2). To investigate the robustness of the SO coupled ground state of ${\mathrm{SrIrO}}_3$, x-ray absorption spectroscopy was carried out at the Ir $L_{2,3}$ edges under hydrostatic pressure up to 50 GPa at room temperature. The effective SO coupling was deduced from the branching ratio (BR) of the Ir $L_2$ and $L_3$ white lines. With increasing pressure, the BR decreases, and the Ir $L_{2,3}$ peak positions shift to higher energies. The number of $5d$ holes remains constant, indicating that the spectral weight redistribution and peak shifts arise from orbital mixing between $t_{2g}$ and $e_g$ related states. The expectation value of the angular part of the SO operator $\langle \mathrm{LS}\rangle$ decreases by $\sim 15\%$ at 50 GPa. This reduction, which is very similar to that observed in the layered iridates, is well explained by an increase of the octahedral crystal field due to the shortening of the Ir-O bond length under compression. Consistent with theoretical predictions, the orbital mixing and $\langle \mathrm{LS}\rangle$ decrease as the crystal field increases. However, the effective SO coupling remains robust against pressure and does not indicate a covalency-driven breakdown within the investigated pressure range.

The single-molecule magnets $\left\{{\mathrm{Mn}}_{70}\right\}$ and $\left\{{\mathrm{Mn}}_{84}\right\}$ are characterized by a 14-site unit cell with $S=2$ spin sites arranged in a circular geometry. Experimentally, these systems exhibit a magnetic ground state with a notably low total spin $S_{\text{tot}}=5–7$. Up to now, this low-spin ground state has been up difficult to describe theoretically due to the complexity of the quantum Heisenberg model for such a large system. In this paper, we fill this gap and demonstrate that the ground state of {${\mathrm{Mn}}_{70}$} and {${\mathrm{Mn}}_{84}$} is in fact governed by a small, finite $S_{\text{tot}}$ in quantitative agreement with the experiment. We employ accurate, large-scale SU(2)-symmetric density-matrix renormalization group calculations for a quantum Heisenberg model with previously published exchange parameters obtained by density-functional theory. We do not find a low-spin state for the same parameters and $S=1$ and thus propose that frustrated systems with $S\ge 2$ are inherently prone to weak ferromagnetic interactions. This could account for the prevalence of similar low-spin Mn-based single-molecule magnets. Finally, we compute the full magnetization curve and find wide plateaus at 10/14, 11/14, 12/14, and 13/14 of the saturation, which can be traced back to nearly independent three-site clusters with broken intercluster bonds.

Topological semimetals in chiral crystals, which possess both structural handedness and band crossings (or nodes) with topological chiral charge, exhibit many exotic physical properties. Here we demonstrate that the structural and electronic chirality of these systems can endow them with another fascinating phenomenon—the intrinsic nonlinear planar Hall effect (INPHE), which is prominent around the nodes and reverses sign upon chirality reversal in opposite enantiomers. Taking chiral tellurium as an example, we reveal an intrinsic orbital mechanism, which manifests diverging orbital magnetic moments with hedgehoglike textures around nodes and, therefore, generates a dominant contribution to the INPHE that is proportional to the topological charge. Furthermore, we show that multifold fermions in topological chiral semimetals with B20 structures (e.g., CoSi and PtAl) induce a giant INPHE conductivity reaching the order of $1\sim 10\mathrm{A}{\mathrm{V}}^{-2}{\mathrm{T}}^{-1}$, which is detectable in experiments. Our study not only relates nonlinear transport to band topology and enantiomer recognition but also offers a new way to explore the exotic physical properties associated with unconventional chiral fermions.

Simulating strongly correlated quantum many-body systems at finite temperatures is a significant challenge in computational physics. In this work, we present a scalable finite-temperature tensor network algorithm for two-dimensional quantum many-body systems. We employ the (fermionic) projected entangled pair state to represent the vectorization of the quantum thermal state, and we utilize a stochastic reconfiguration method to cool down the quantum states from infinite temperature. We validate our method by benchmarking it against the two-dimensional antiferromagnetic Heisenberg model, the $J_1-J_2$ model, and the Fermi-Hubbard model, comparing physical properties such as internal energy, specific heat, and magnetic susceptibility with results obtained from stochastic series expansion, exact diagonalization, and determinant quantum Monte Carlo.

The kagome material ${\mathrm{CsTi}}_3{\mathrm{Bi}}_5$, which is isostructural to the extensively studied charge-density-wave (CDW) compound ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, exhibits intriguing electronic features within its two-dimensional kagome lattices of titanium atoms. Here, we perform optical spectroscopic measurements together with the first-principles calculations for single-crystalline ${\mathrm{CsTi}}_3{\mathrm{Bi}}_5$ to investigate its electronic properties comprehensively. It is found that the overall optical spectra exhibit surprising similarity to those of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, even in the CDW state. Nevertheless, the existence of CDW instability is ruled out in ${\mathrm{CsTi}}_3{\mathrm{Bi}}_5$. Via careful comparison to the optical responses of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, we attribute this difference to a significant reduction in the itinerant carrier density of ${\mathrm{CsTi}}_3{\mathrm{Bi}}_5$, which is associated with the absence of Van Hove singularity near the Fermi level at the $M$ point. These results support the scenario that the CDW in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ is driven by the nesting of Van Hove singularity. Additionally, we unveil some exotic low-lying absorption features which provide clear evidence of flat bands in ${\mathrm{CsTi}}_3{\mathrm{Bi}}_5$. Our findings contribute to a deeper understanding of exotic phenomena in ${\mathrm{CsTi}}_3{\mathrm{Bi}}_5$ and provide valuable insights into the role of Van Hove singularity in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$.

It has long been puzzling that fractional quantum Hall states in the first excited Landau level (1LL) often differ significantly from their counterparts in the lowest Landau level. We show that the dispersion of composite fermions (CFs) is a deterministic factor driving the distinction. We find that CFs with two quantized vortices in the 1LL have a non-quasiconvex dispersion. Consequently, in the filling fraction $7/3$, CFs occupy the second $\mathrm{\Lambda }$-level instead of the first. The corresponding ground state wave function, based on the CF wave function ansatz, is identified to be the fermionic Hafnian wave function rather than the Laughlin wave function. The conclusion is supported by numerical evidence from exact diagonalizations in both disk and spherical geometries. Furthermore, we show that the dispersion becomes quasiconvex in wide quantum wells or for CFs with four quantized vortices in the filling fraction $11/5$, coinciding with observations that the distinction between the Landau levels disappears under these circumstances.

We investigate the intrinsic linear and nonlinear ac orbital Hall (OH) conductivity in a two-dimensional system, arising from the transverse motion of electrons with finite orbital angular momentum in an applied electric field. Using the quantum kinetic approach, we show that the total OH conductivity comprises both interband and intraband contributions. However, the interband contribution dominates over the intraband in the high frequency regime. Our analysis predicts that the interband part of the linear OH conductivity is governed by the Fermi sea contribution. Meanwhile the nonlinear responses, including second harmonic and rectification effects, stem from the interplay between the Fermi sea and Fermi surface contributions. We find that the broken inversion symmetry in the system yields nonzero orbital angular momentum and consequently the orbital Hall response. In addition, the linear OH conductivity exhibits a resonant peak and a sign transition depending on the gap and Fermi energy values relative to the incident energy. Unlike the linear, the second harmonic OH conductivity shows two sign conversions as the incident energy approaches to the gap value and twice its value. These findings shed light on the modulation of field-driven orbital Hall conductivity with frequency, Fermi energy, and band gap.

We study tilted chains of spinless fermions in the presence of the nearest-neighbor density-density interaction for which the noninteracting counterpart displays Stark localization. We demonstrate that the latter two-body interaction can be decomposed into two (orthogonal) parts which, respectively, commute and do not commute with the single-particle Hamiltonian. We derive an explicit form of the noncommuting part that decreases with tilt and describes the nearest-neighbor correlated hopping and the pair-hopping interaction. When the density-density coupling is replaced by the pair-hopping interaction of the same magnitude then the charge dynamics may be faster by a few orders of magnitude than in the original model.