We present a comprehensive study of the thermoelectric (TE) properties of the layered rare-earth ($R$) tritelluride $R\mathrm{T}{\mathrm{e}}_3 (R=\mathrm{Gd},\mathrm{Tb},\mathrm{Dy},\mathrm{Ho},\text{and}\mathrm{Er})$ single crystals, which recently drew attention for the discovery of incommensurate charge density waves (CDWs) along two crystallographic directions of the Te layer. Pronounced anomalies observed in the electrical resistivity (ρ), Seebeck coefficient ($S$), thermal conductivity (κ), and specific heat ($C_{\mathrm{p}}$) measurements with temperature ($T$) highlight two CDW transitions for $R$ = Ho and Er and one CDW transition for $R=\mathrm{Gd},\mathrm{Tb},\text{and}\mathrm{Dy}$. The ρ($T$) and $S$($T$) data showed metallic conductions with less electron correlations, showing an increase in their values below the transitions. It suggests the opening of a gap in the electronic band structure, indicating a decrease with the size of $R$ ions. Analysis of κ($T$) data revealed that the observed variations in heat conduction at the CDW transitions are primarily electronic driven. Furthermore, the $C_{\mathrm{p}}$($T$) of $R\mathrm{T}{\mathrm{e}}_3$ displays broad anomalies at CDW transitions, and the associated entropy change for different $R$'s can be quantitatively explained by a weak coupling mean-field model. The obtained TE properties result in an enhancement in the figure of merit $\mathit{ZT}$ of $R\mathrm{T}{\mathrm{e}}_3$ due to the increase in the power factor below the CDW transition.

Many-body eigenstates that are neither thermal nor many-body localized (MBL) have been numerically found in certain interacting chains with moderate quasiperiodic potentials. The energy regime consisting of these nonergodic but extended (NEE) eigenstates has been extensively studied as a possible many-body mobility edge between the energy-resolved MBL and thermal phases. Recently, the NEE regime was proposed to be a prethermal phenomenon that generally occurs when different operators spread on sizably different timescales. Here, we numerically examine the mutual independence among the NEE, MBL, and thermal regimes through the lens of eigenstate entanglement spectra (ES). Given the complexity and rich information embedded in ES, we develop an unsupervised learning approach designed to quantify the mutual independence among general phases. Our method is first demonstrated on an illustrative toy example that uses RGB color data to represent phases, and then applied to the ES of an interacting generalized Aubry-Andre model from weak to strong potential strength. We find that while the MBL and thermal regimes are mutually independent, the NEE regime is dependent on the former two and smoothly emerges as the potential strength decreases. We attribute this numerical finding to the fact that the ES data in the NEE regime exhibit both an MBL-like fast decay and a thermal-like long tail.

Elucidating the emergence of long-range magnetic ordering from its precursor short-range magnetic ordering (SRMO) in two-dimensional van der Waals materials holds profound implications for fundamental research and technological advancements. However, directly observing the intricate stages of this magnetic dimensional crossover (MDC) remains a significant experimental challenge. While magnetoelastic coupling offers a promising avenue, detecting the minute lattice response to SRMO proves challenging. To meet this goal, we have executed an alternative approach by employing picosecond acoustic strain pulses generated by femtosecond lasers to probe the various stages of MDC through the magnetoelastic coupling. By analyzing the shape of the strain pulse in both the time and frequency domains as a function of temperature, we clearly demonstrate the detection of the subtle influence of spin fluctuations on the lattice. Additionally, the ultrafast carrier dynamics also show signatures of MDC. Our measurements pave the way toward characterizing magnetic materials in time-resolved experiments that are crucial in designing a new generation of spin-based optoelectronic devices.

Spin current flowing between femtosecond laser pulse (fsLP) driven ferromagnetic metal and adjacent normal metal (NM) hosting strong spin-orbit coupling is invariably invoked to explain terahertz (THz) radiation believed to be emitted solely by the NM layer. Despite being such a central concept, the microscopic origin of interlayer spin current remains vague. It is also unclear if it directly imprints its time dependence onto emitted THz radiation because far-field radiation can only be emitted by time-dependent charge current, while a potentially large number of complex spin-to-charge conversion mechanisms can obscure direct relation between interlayer spin current and converted charge current within the NM layer. Here, we employ a recently developed [A. Kefayati et al., Phys. Rev. Lett. 133, 136704 (2024)] time-dependent density functional theory plus Jefimenko equations approach to extract spin current between Co and a NM = Pt or NM = W layer, where Co is driven by fsLP responsible for its demagnetization, i.e., shrinking of its magnetization vector, $M^y\left(t\right)/M^y(t=0)<1$. By comparing time dependence of spin current with those of other relevant quantities, we find that ($i$) spin current is generated by demagnetization dynamics because it follows closely $d{M}^y/dt$, thus it is an example of a quantum pumping phenomenon that cannot be captured by phenomenological notions (such as “spin voltage”) and related semiclassical transport theories; ($\mathit{ii}$) time dependence of pumped spin current does not follow closely that of charge current emerging within the NM layer via spin-to-charge conversion mechanisms; (iii) THz emission can be governed by charge currents (i.e., its time derivative entering the Jefimenko equations) within both the Co layer and NM layer, but in different times frames. We also unravel a special case of NM = W where spin-to-charge conversion by the inverse spin Hall effect and its contribution to THz emission is suppressed, despite large spin Hall angle of W, because of localization of excited electrons onto the outer unfilled $d$ orbitals of W.

We report the thermal and electrical conductivity data for the magnetic Weyl semimetal SmAlSi measured in a magnetic field ($B$) with two different orientations. In one case, $B$ was applied perpendicular to the heat or charge current; in the other they were parallel. For both configurations, the magnetic field affects the magnetic structure identically as $B$ is always parallel to the equivalent tetragonal axis. Our results indicate that phonon heat transport in response to the magnetic field exhibits strong anisotropy at low temperature: it appears to be independent of $B$ in the perpendicular configuration but is strongly suppressed in the parallel configuration. Understanding this unusual behavior can lead to designing better materials for thermoelectricity or directional heat switches.

We introduce an extension of the nonequilibrium dynamical mean-field theory to incorporate the effects of static random disorder in the dynamics of a many-particle system by integrating out different disorder configurations resulting in an effective time-dependent density-density interaction. We use this method to study the nonequilibrium transient dynamics of a system described by the Fermi Anderson-Hubbard model following an interaction and disorder quench. The method recovers the solution of the disorder-free case for which the system exhibits qualitatively distinct dynamical behaviors in the weak-coupling (prethermalization) and strong-coupling regimes (collapse-and-revival oscillations). However, we find that weak random disorder promotes thermalization. In the weak-coupling regime, the jump in the quasiparticle weight in the prethermal regime is suppressed by random disorder, while in the strong-coupling regime, random disorder reduces the amplitude of the quasiparticle weight oscillations. These results highlight the importance of disorder in the dynamics of realistic many-particle systems.

Motivated by the abundance of symmetry breaking states in magic-angle twisted bilayer graphene and other two-dimensional materials, we study superconducting (SC) and charge orders in two-dimensional topological flat bands in the strong correlation regime. By relating the half-filled two-dimensional (2D) topological flat bands to the surface states of 3D topological insulators in symmetry class AIII, we reveal the topological obstruction to the formation of gapped SC and intervalley charge orders without intrinsic topological orders, in the presence of the antiunitary particle-hole symmetry at half filling. This is a generalization of the Li-Haldane arguments for nodal superconductivity to strongly interacting electrons. In contrast to the $\mathbb{Z}$-valued obstruction derived from the noninteracting band topology, the topological obstruction of interacting electrons in half-filled flat bands has a ${\mathbb{Z}}_8$ classification, depending on the charge (valley) Chern number of the superconducting (intervalley charge) orders. This is demonstrated by an interacting Hamiltonian for half-filled flat bands with a net Chern number $C=4$, where superconductivity and ${\mathbb{Z}}_2$ topological order coexist in a gapped ground state with particle-hole symmetry.

We propose two geometries to realize a significant optomechanical-type coupling (XZ coupling) between magnons and a two-dimensionl microwave cavity mode. In both setups the cavity is analogous to the mechanical oscillator in a conventional optomechanical setup. The backaction effects are calculated with realistic experimental parameters. The analytical results show that we can not only make the backaction damping (antidamping) rate larger than the bare microwave resonator damping rate, but that we can also achieve quantum squeezing of the resonator where the uncertainty in one quadruture (charge or current) is smaller than its zero-point fluctuation.

We study a magnetic domain wall in the ferromagnetic phase in chiral magnets in two dimensions with an in-plane easy-axis anisotropy and an out-of-plane Zeeman magnetic field, and find a chiral soliton lattice (spiral) phase beside a ferromagnetic phase inside the domain line, where the former represents a domain-wall skyrmion crystal from the bulk point of view. We first determine the phase diagram on the domain wall by numerically constructing domain-wall solutions. We then analytically reproduce the phase diagram in a domain-wall theory (a chiral double sine-Gordon model) that we construct within the moduli approximation by treating the Zeeman magnetic field perturbatively. While we find good agreements between the phase diagrams of the numerical and effective theory methods, the numerical solution exhibits a decomposition of the topological charge into a bimeron which cannot be captured by the effective theory.

We consider the spin dynamics of a normal metal–ferromagnet heterostructure, with emphasis on spin-nutation terms arising from a dynamical Ruderman-Kittel-Kasuya-Yosida interaction. We find that the spin-nutation term is anisotropic in spin space due to the broken time-reversal symmetry of the ferromagnet. This contrasts with what one obtains in the paramagnetic state, where the nutation term is isotropic in spin space. We compute the effects this has on the magnetization dynamics derived from a Landau-Lifshitz-Gilbert equation. In particular, due to broken time-reversal symmetry, we predict a qualitative change in the zero-field ferromagnetic resonance spectrum which is present up to the Curie temperature. We propose that this is a strong indicator of the existence of nutation in ferromagnetically ordered spin systems.

Kagome materials, which are composed of hexagons tiled with a shared triangle, have inspired enormous interest due to their unique structures and rich physical properties; exploring superconducting material systems with new kagome structures is still an important research direction. Here, we predict a type of kagome superconductor, ${M\mathrm{Pd}}_5$ (M is a group-IIA metal element), and identify that it exhibits coexistence of superconductivity and nontrivial topological properties. We uncover its phonon-mediated superconductivity by the density functional theory for superconductors, predicting the superconducting transition temperatures $\left(T_{\mathrm{c}}\right)$ of 2.64, 2.03, and 1.50 K for ${\mathrm{CaPd}}_5$, ${\mathrm{SrPd}}_5$, and ${\mathrm{BaPd}}_5$, respectively. These $T_{\mathrm{c}}$ can be effectively tuned through the application of external pressure and electron doping. The present results also demonstrate that ${M\mathrm{Pd}}_5$ have topological properties; e.g., ${\mathrm{CaPd}}_5$ shows topological nontrivial intersection near the Fermi level $\left(E_{\mathrm{F}}\right)$. Our results indicate that ${M\mathrm{Pd}}_5$ materials can be an emerging material platform with rich exotic physics in their kagome structures, and render themselves excellent candidates for superconducting and advanced functional materials that could be utilized in topological quantum computing and information technology.

Finding and designing ferromagnets that operate above room temperature is crucial in advancing high-performance spintronic devices. The pioneering van der Waals (vdW) ferromagnet ${\mathrm{Fe}}_3{\mathrm{GaTe}}_2$ has extended the way for spintronic applications by achieving a record-high Curie temperature among its analogs. However, the physical mechanism of increasing Curie temperature in this material still needs to be explored. Here, we systematically investigate the electronic structures and magnetic properties of ${\mathrm{Fe}}_3{\mathrm{GaTe}}_2$ as a function of temperature using strongly correlated calculations, reconciling the dual nature of $d$ electrons with both localization and itinerant characters. Significantly, our paper reveals the emergence of quasiparticle flat bands driven by many-body interactions, which enhance magnetic stability through a positive feedback mechanism. Furthermore, our results demonstrate the hybridization of these flat bands at low temperatures, indicating the possible presence of heavy fermion behavior in this system. Our findings suggest that tunable flat bands near the Fermi level may serve as a key factor in realizing materials with high magnetic transition temperatures and strong magnetic anisotropy. This paper provides a promising pathway for exploring next-generation spintronic devices utilizing vdW flat band systems.

The transfer of quantum information between many-qubit states is a subject of fundamental importance in quantum science and technology. We consider entanglement swapping in critical quantum spin chains, where the entanglement between the two chains is induced solely by the Bell-state measurements. We employ a boundary conformal field theory (CFT) approach and describe the measurements as conformal boundary conditions in the replicated field theory. We show that the swapped entanglement exhibits a logarithmic scaling, whose coefficient takes a universal value determined by the scaling dimension of the boundary condition changing operator. We apply our framework to the critical spin-$\frac{1}{2}$ XXZ chain and determine the universal coefficient by the boundary CFT analysis. We also numerically verify these results by the tensor-network calculations. Possible experimental relevance to Rydberg atom arrays is briefly discussed.

Together with ${\mathrm{EuGa}}_4$ and ${\mathrm{EuAl}}_4, {\mathrm{EuAl}}_2{\mathrm{Ga}}_2$ belongs to the ${\mathrm{BaAl}}_4$ structure type with space group $I4$/mmm. ${\mathrm{EuAl}}_2{\mathrm{Ga}}_2$ develops an incommensurate charge density wave (CDW) at temperatures below $T_{\mathrm{CDW}}=51\mathrm{K}$. On the basis of temperature-dependent single-crystal x-ray diffraction data, the incommensurately modulated CDW crystal structure of ${\mathrm{EuAl}}_2{\mathrm{Ga}}_2$ is determined to possess orthorhombic symmetry Immm(0000γ)$s0000$. This symmetry is different from the orthorhombic Fmmm-based symmetry of the CDW state of ${\mathrm{EuAl}}_4$. Nevertheless, both symmetries, Immm(00γ)$s00$ and Fmmm(00γ)$s00$, lead to the same conclusion, that the CDW is supported by the layers of Al1 type atoms, while the Eu and Al2 or Ga atoms are not directly involved in CDW formation. The different symmetries of the CDW states of ${\mathrm{EuAl}}_4$ and ${\mathrm{EuAl}}_2{\mathrm{Ga}}_2$, as well as the observation of negative thermal expansion in the CDW state of ${\mathrm{EuAl}}_2{\mathrm{Ga}}_2$, might be explained by the effects of Ga substitution in the latter compound.

In twisted moiré superlattices, the inherent periodic potential fields can form flat bands, causing many novel physical phenomena with strong correlation effects. In existing research findings, moiré flat bands with strong charge localization can be achieved by reducing the twist angle to increase the moiré period or selecting materials with large band edge energy differences that correspond to deep potential wells. Here, we propose a design approach for realizing flat bands in moiré superlattices at large twist angles even under shallow potential wells. We find that charges with greater effective mass are more susceptible to localization in the superlattice in spite of small potential well depth. We have confirmed this idea in twisted ${\mathrm{MoSe}}_2\_\mathrm{TeMoS}$ bilayers, achieving an ultraflat energy band with a bandwidth of 0.8 meV (1.3 meV) at a twist angle of $7.34{}^{\circ }$ based on $AB$ ($AA$) stacking configuration with the band edge energy difference of only 13.5 meV (22.6 meV), due to the large hole effective mass of $11.8m_0$ ($11.6m_0$). Our discovery provides an approach for achieving ultraflat energy bands at large angles, further enriching the flat-band mechanism.

Oxide heterostructures based on $\mathrm{SrTi}{\mathrm{O}}_3$ have emerged as a rich platform for exploring physical phenomena, most notably conductivity at interfaces between insulators. In this study, we investigate the electronic properties of an oxide-semiconductor heterostructure—$\mathrm{SrTi}{\mathrm{O}}_3$ films grown epitaxially on Si(001). The lattice mismatch induces epitaxial strain, breaking the cubic symmetry of $\mathrm{SrTi}{\mathrm{O}}_3$ and resulting in tetragonal distortion. Magnetotransport measurements reveal that the temperature and magnetic field dependence of the conductivity are dominated by two-dimensional quantum effects, weak localization, and electron-electron interactions. The low-temperature electronic properties indicate quantum confinement, strong electron correlations, exchange interactions, and Zeeman spin splitting. These findings underscore the potential of the $\mathrm{SrTi}{\mathrm{O}}_3$/Si heterostructure for designing oxide-based quantum devices.