We study the possible signatures of prethermal strong Hilbert space fragmentation (HSF) for one-dimensional (1D) fermions subjected to a periodic drive. We extend the results of Ghosh et al. [Phys. Rev. Lett. 130, 120401 (2023)] to show the possibility of such fragmentation for a large class of experimentally relevant drive protocols. Moreover, we demonstrate the persistence of HSF when the fermion chain is taken away from half filling. Both analyses indicate the robustness of the fragmentation phenomenon reported earlier. We also provide an alternate derivation of the Floquet Hamiltonian of the driven chain which yields insight into the generic nested commutator structure of its higher order terms. Finally, we study the density-density out-of-time-correlators (OTOC) of the driven chain both away and near the special drive frequencies at which its first-order Floquet Hamiltonian exhibits fragmentation. We show that these OTOCs, for a chain with open boundary conditions, exhibit a distinct periodic unscrambling of information at special drive frequencies; such unscrambling can therefore serve as a marker of prethermal HSF. We provide an approximate analytic explanation of the role of HSF behind such periodic unscrambling and discuss experiments which can detect signatures of strong HSF in such driven chains.

We investigate the coherent enhancement of inherently weak magnetic interactions in rare-earth orthoferrite ${\mathrm{SmFeO}}_3$ as a functional material for spintronic applications using a realistic model of dissipative spin dynamics that are linearly and quadratically coupled to laser-driven infrared-active phonons. When linear coupling dominates, we discover a magnetophononic dynamical first-order phase transition in the nonequilibrium steady state which can inhibit strong enhancement of magnetic interactions. By contrast, when quadratic spin-phonon coupling dominates, no phase transition exists at experimentally relevant parameters. By utilizing a chirp protocol, the phase transition can be engineered, enabling stronger magnetic interactions. We also discuss the route for experimental observation of our results.

Infinite-layer nickelates show high-temperature superconductivity, and the experimental phase diagram agrees well with the one simulated within the dynamical vertex approximation ($\mathrm{D}\mathrm{\Gamma }\mathrm{A}$). Here, we compare the spin-fluctuation spectrum behind these calculations to resonant inelastic x-ray scattering experiments. The overall agreement is good. This independent cross validation of the strength of spin fluctuations strongly supports the scenario, advanced by $\mathrm{D}\mathrm{\Gamma }\mathrm{A}$, that spin fluctuations are the mediator of the superconductivity observed in nickelates.

Using an ultrahigh resolution ($\mathrm{\Delta }E\sim 0.1\mathrm{eV}$) setup to measure electronic features in x-ray Thomson scattering (XRTS) experiments at the European XFEL in Germany, we have studied the collective plasmon excitation in aluminium at ambient conditions, which we can measure very accurately even at low momentum transfers. As a result, we can resolve previously reported discrepancies between ab initio time-dependent density functional theory simulations and experimental observations. The demonstrated capability for high-resolution XRTS measurements will be a game changer for the diagnosis of experiments with matter under extreme densities, temperatures, and pressures, and unlock the full potential of state-of-the-art x-ray free electron laser (XFEL) facilities to study planetary interior conditions, to understand inertial confinement fusion applications, and for material science and discovery.

We introduce stochastic techniques that enable the simulations of polaritons resulting from placing giant two-dimensional molecular aggregate crystals with ${10}^8$ interacting excitonic dyes in realistic multimode cavities. We show that the intermolecular coupling protects the formation of polariton states in the face of strong molecular disorder due to persistent delocalization of the dark molecular states. This demonstrates the nontrivial role of internal aggregate Hamiltonian in polariton properties, and the new computational method opens horizons for stochastic simulations of related systems.

Rashba spin-orbit coupling is a quintessential spin interaction appearing in virtually any electronic heterostructure. Its paradigmatic spin texture in the momentum space forms a tangential vector field. Using first-principles investigations, we demonstrate that in twisted homobilayers and heteromultilayers, the Rashba spin texture can be predominantly radial, parallel to the momentum. Specifically, we study four experimentally relevant structures: twisted bilayer graphene (Gr), twisted bilayer ${\mathrm{WSe}}_2$, and twisted multilayers ${\mathrm{WSe}}_2/\mathrm{Gr}/{\mathrm{WSe}}_2$ and ${\mathrm{WSe}}_2/\mathrm{Gr}/\mathrm{Gr}/{\mathrm{WSe}}_2$. We show that the Rashba spin texture in such structures can be controlled by an electric field, allowing to tune it from radial to tangential. Such spin-orbit engineering should be useful for designing spin-charge conversion and spin-orbit torque schemes, as well as for controlling correlated phases and superconductivity in van der Waals materials.

For a better understanding of the outstanding real-time photorefractive medium ${\mathrm{LiNbO}}_3$:(Bi,Mg) and excitonic processes in similar systems in general, stoichiometric ${\mathrm{LiNbO}}_3$ (SLN) crystals grown by two different methods and doped by Bi, Fe, or (Bi,Mg) have been investigated using low-intensity near-UV irradiation and absorption spectroscopy. Tracking down the incorporation of dopants and impurities including Fe and H by chemical and IR-UV spectroscopic analyses we assign the various spectroscopic features to specific defect complex types. Absorption bands near 4 eV overlapping the UV band edge and polarized along Nb–O bonds are ascribed to the generation of self-trapped excitons (STEs) pinned to dipolar defects consisting of $\mathrm{B}{\mathrm{i}}^{3+}$ or $\mathrm{F}{\mathrm{e}}^{3+}$ ions and their charge compensators, becoming exceptionally long-lived in the presence of lone pairs on ${\mathrm{Bi}}^{3+}$ ions. Near-UV illumination induces persistent additional absorption bands at ≈2.7 and ≈3.4 eV in Bi-single-doped crystals which can be eliminated by a short annealing above $\approx 150{}^{\circ }\mathrm{C}$ or fade within a few months in the dark. These and similar photochromic bands in SLN:(Bi,Mg) are attributed to further excitations of pinned STEs, resulting in charge release. Shortening of the buildup time of the photochromic bands in (Bi,Mg)-codoped crystals is ascribed to the absence of ${\mathrm{Nb}}_{\mathrm{Li}}$ antisite complexes serving as exciton sinks in under-threshold LN. Due to its markedly different properties an additional stable narrow band at 3.24 eV always present in SLN:(Bi,Mg) is attributed to fast reversible charge transfer processes from ${\mathrm{O}}^{2–}$ to $\mathrm{B}{\mathrm{i}}^{5+}$ ions on the Nb site. Processes on widely differing timescales are predicted for one- and two-photon excitations involving different excited states, relevant for further optimization of the system.

Here we report on a comprehensive investigation of transverse magnetothermoelectric properties of the equiatomic quaternary Heusler alloys $\mathrm{CrRu}X\mathrm{Ge}$ ($X$ = Co and Mn). Magnetic measurements reveal the presence of a glassy magnetic ground state owing to the energetically competing ferromagnetic and antiferromagnetic phases in CrRuCoGe at low temperatures, whereas CrRuMnGe exhibits soft ferromagnetic behavior with a weak martensitic transformation close to room temperature. The temperature-dependent anomalous Nernst coefficient $\left(S_{\mathrm{ANE}}\right)$ of CrRuMnGe shows noticeable changes around the martensitic transformation. While CrRuCoGe exhibits positive $S_{\mathrm{ANE}}$, CrRuMnGe exhibits negative $S_{\mathrm{ANE}}$ throughout the measured temperature range. We demonstrate that the contribution of the anomalous transverse thermoelectric conduction dominates that of the anomalous Hall effect acting on the thermally generated carrier flow induced by the longitudinal Seebeck effect, which gives rise to the opposite polarity of $S_{\mathrm{ANE}}$ in these two alloys. Our detailed analysis indicates that the origin of the observed anomalous Nernst effect (ANE) in both of these alloys is dominated by the asymmetric skew scattering of charge carriers in the measured temperature regime. The sign change and tunability of ANE presented in this study provide a step forward toward the development of ANE-based efficient thermopile devices operating at room temperature utilizing the equiatomic quaternary Heusler alloys.

We study the electronic excitation spectra in solid molecular hydrogen (phase I) at ambient temperature and 5- to 90-GPa pressures using quantum Monte Carlo methods and many-body perturbation theory. In this range, the system changes from a wide-gap molecular insulator to a semiconductor, altering the nature of the excitations from localized to delocalized. Computed gaps and spectra agree with experiments, proving the ability to predict accurately band gaps of many-body systems in the presence of nuclear quantum and thermal effects.

Solving the time-dependent quantum many-body Schrödinger equation is a challenging task, especially for states at a finite temperature, where the environment affects the dynamics. Most existing approximating methods are designed to represent static thermal density matrices, 1D systems, and/or zero-temperature states. In this work, we propose a method to study the real-time dynamics of thermal states in two dimensions, based on thermofield dynamics, variational Monte Carlo, and neural-network quantum states. To this aim, we introduce two novel tools: (i) a procedure to accurately simulate the cooling down of arbitrary quantum variational states from infinite temperature, and (ii) a generic thermal (autoregressive) recurrent neural-network (ARNNO) Ansatz that allows for direct sampling from the density matrix using thermofield basis rotations. We apply our technique to the transverse-field Ising model subject to an additional longitudinal field and demonstrate that the time-dependent observables, including correlation operators, can be accurately reproduced for a $4\times 4$ spin lattice. We provide predictions of the real-time dynamics on a $6\times 6$ lattice that lies outside the reach of exact simulations.

Manipulating topological states is a topic of vigorous research. However, the impact of such topological phase transitions on the quasiparticle dynamics remains elusive. In this work, we present the effects of a transition from a strong to weak topological insulator in ${\mathrm{HfTe}}_5$ as a function of Te vacancy concentration. We observed a significant transition from distinct sharp surface states and Dirac crossing to a Fermi-liquid-like quasiparticle state in which these surface-localized features are heavily suppressed. Additionally, by inducing the same effect through applied uniaxial stress, we demonstrate that changes in the lattice constants play the foremost role in determining the electronic structure, self-energy, and topological states of ${\mathrm{HfTe}}_5$. Our results demonstrate the possibility of using both defect chemistry and strain as control parameters for topological phase transitions and associated many-body physics.

We report an investigation of the effect of substitution of Y for Tm in ${\mathrm{Tm}}_{1-x}{\mathrm{Y}}_x{\mathrm{VO}}_4$ via low-temperature heat capacity measurements, with the yttrium content $x$ varying from 0 to 0.997. Because the Tm ions support a local quadrupolar (nematic) moment, they act as reporters of the local strain state in the material, with the splitting of the ion's non-Kramers crystal field ground state proportional to the quadrature sum of the in-plane tetragonal symmetry-breaking transverse and longitudinal strains experienced by each ion individually. Analysis of the heat capacity, therefore, provides detailed insights into the distribution of local strains that arise as a consequence of the chemical substitution. These local strains suppress long-range quadrupole order for $x>0.22$, and result in a broad Schottky-like feature for higher concentrations. Heat capacity data are compared to expectations for a distribution of uncorrelated (random) strains. For dilute Tm concentrations, the heat capacity cannot be accounted for by randomly distributed strains, demonstrating the presence of significant strain correlations between sites. For intermediate Tm concentrations, these correlations must still exist, but the data cannot be distinguished from that which would be obtained from a two-dimensional Gaussian distribution. The crossover between these limits is discussed in terms of the interplay of key lengthscales in the substituted material. The central result of this work, namely that local strains arising from chemical substitution are not uncorrelated, has implications for the range of validity of theoretical models based on random effective fields that are used to describe such chemically substituted materials, particularly when electronic nematic correlations are present.

Alkali superoxides ${A\mathrm{O}}_2$ $(A=\text{Na}, \mathrm{K}, \mathrm{Rb}, \mathrm{Cs})$, due to an open $p$ shell of the oxygen ion ${\mathrm{O}}_2^{-}$ with degenerate $\pi$ orbitals, have spin and orbital degrees of freedom. The complex magnetic, orbital, and structural phase transitions observed experimentally in this family of materials are only partially understood. Based on density functional theory, we derive a strong-coupling effective model for the isostructural compounds ${A\mathrm{O}}_2$ $(A=\text{K}, \mathrm{Rb}, \mathrm{Cs})$ from a two-orbital Hubbard model. We find that ${\mathrm{CsO}}_2$ has highly frustrated exchange interactions in the $a\text{−}b$ plane, while the frustration is weaker for ${\mathrm{RbO}}_2$ and ${\mathrm{KO}}_2$. We solve the resulting Kugel-Khomskii model in the mean-field approximation. We show that ${\mathrm{CsO}}_2$ exhibits an antiferro-orbital (AFO) order with the ordering vector $\mathit{q}=(1,0,0)$ and a stripe antiferromagnetic order with $\mathit{q}=(1/2,0,0)$, which is consistent with recent neutron scattering experiments. We discuss the role of the $\pi$-orbital degrees of freedom for the experimentally observed magnetic transitions and interpret the as-yet-unidentified $T_{\mathrm{s}2}=70\mathrm{K}$ transition in ${\mathrm{CsO}}_2$ as an orbital ordering transition.

The electronic structure of the topmost layer in ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ in the close vicinity of the Fermi level is investigated by angle-resolved photoemission spectroscopy with a 7-eV laser. We find that the spin-orbit coupling (SOC) predicted as 100 meV by the density functional theory calculations is enormously enhanced in a real material up to 250 meV, even more than that of bulk state (200 meV), by the electron-correlation effect increased by the octahedral rotation in the crystal structure. This causes the formation of highly orbital-mixing small Fermi pockets and reasonably explains why the orbital-selective Mott transition is not realized in perovskite oxides with crystal distortion. Interestingly, Hund's metal feature allows the quasiparticle generation only near $E_{\mathrm{F}}$, restricting the spectral gap opening derived by band hybridization within an extremely small binding energy ($<$ 10 meV). Furthermore, it causes coherent-incoherent crossover, making the Fermi pockets disappear at elevated temperatures. The anomalous Fermi pockets are characterized by the dichotomy of the orbital-isolating Hund's coupling and the orbital-mixing SOC, which is key to understanding the nature of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$.

We present an approach to tame the growth of entanglement during time evolution by tensor network methods. It combines time evolution in the complex plane with a perturbative and controlled reconstruction of correlation functions on the real time axis. We benchmark our approach on the single impurity Anderson model. Compared to purely real time evolution, the complex time evolution significantly reduces the required bond dimension to obtain the spectral function. Notably, our approach yields self-energy results with high precision at low frequencies, comparable to numerical renormalization group results, and it successfully captures the exponentially small Kondo energy scale.

Forming a semiconductor alloy is a common practice to extend material properties for specific applications. While empirical continuous rules have been proposed and extensively validated to predict property changes in conventional alloys, there are certain isovalent alloys that exhibit discontinuous variations in electronic structures, defying the application of established rules. However, the underlying cause of this phenomenon has not been clearly stated. Through rigorous first-principles calculations on a prototypical α-${\left({\mathrm{Rh}}_x{\mathrm{Ga}}_{1\text{–}x}\right)}_2{\mathrm{O}}_3$ alloy, we find a steplike, discontinuous variation in the band gap. A thorough examination reveals that this is correlated with the unconventional evolution of wavefunction characters at the band edges and the associated wavefunction localization on the alloying atomic site, so the band gap deviates strongly from the alloy-averaged properties. These results offer insights into the unique optoelectronic properties of semiconductor alloys with dissimilar band-edge wavefunction characters and emphasize the need to account for the specific band-edge wavefunction character differences in the two endpoint materials for more dependable predictions of property trends in alloys.

Gauging a finite subgroup of a global symmetry can map conventional phases and phase transitions to unconventional ones. In this work, we study, as a concrete example, an emergent ${\mathbb{Z}}_2$-gauged system with global symmetry $\text{U}\left(1\right)$, namely, the ${\mathbb{Z}}_2$-gauged Bose-Hubbard model both in 1D and in 2D. In certain limits, there is an emergent mixed 't Hooft anomaly between the quotient $\tilde{\mathrm{U}}\left(1\right)$ symmetry and the dual ${\widehat{\mathbb{Z}}}_2$ symmetry. In 1D, the superfluid phase is mapped to an intrinsically gapless symmetry-protected topological (SPT) phase, as supported by density-matrix renormalization group (DMRG) calculations. In 2D, the original superfluid-insulator transition becomes a generalized deconfined quantum critical point (DQCP) between a gapless SPT phase, where an SPT order coexists with Goldstone modes, and a $\tilde{\mathrm{U}}\left(1\right)$-symmetry-enriched topological (SET) phase. We also discuss the stability of these phases and the critical points to small perturbations and their potential experimental realizations. Our work demonstrates that partial gauging is a simple and yet powerful approach in constructing novel phases and quantum criticalities.

Broken of translational symmetry plays a vital role in the stabilization of three-dimensional magnetic skyrmions. The absence of exchange neighbours at truncated surfaces leads to surface twist effect, resulting in twisted helicity angle of the skyrmions. Recently, it was reported in Zhang et al. [Proc. Natl. Acad. Sci. USA 115, 6386 (2018)] that the observed surface twist effect is over an order of magnitude more pronounced than the theoretical predictions. Nevertheless, the underlying mechanism that leads to such discrepancy has not been resolved yet. In order to address this long-standing issue, we performed depth-resolved circular dichroic resonant elastic x-ray scattering (CD-REXS) measurements on the skyrmion lattice phase in ${\mathrm{Cu}}_2{\mathrm{OSeO}}_3$ over a wide temperature range. It is found that the measured skyrmion helicity angle profile is highly temperature-dependent, which cannot be quantitatively explained by the temperature-varying micromagnetic parameters alone. By systematically ruling out other possible effects, we conclude that a giant surface-type Dzyaloshinskii-Moriya interaction emerges due to the ferroelectric polarization at the surface of ${\mathrm{Cu}}_2{\mathrm{OSeO}}_3$. Our results provide insights into the complex interplay between surface and bulk interactions in the formation of magnetic skyrmions and offer new possibilities for designing skyrmionic devices.

Topoelectrical circuits are metamaterial realizations of topological features of condensed matter systems. In this work, we discuss experimental methods that allow a fast and straightforward detection of the spectral features of these systems from the two-point impedance of the circuit. This allows us to deduce the full spectrum of a topoelectrical circuit consisting of $N$ sites from a single two-point measurement of the frequency-resolved impedance. In contrast, the standard methods rely on $N^2$ measurements of admittance matrix elements with a subsequent diagonalization on a computer. We experimentally test our approach by constructing a Fibonacci topoelectrical circuit. Although the spectrum of an infinite Fibonacci chain is fractal, i.e., more complex than the spectra of periodic systems, our approach is successful in recovering its eigenvalues. Our work promotes the topoelectrical circuits as an ideal platform to measure spectral properties of various (quasi)crystalline systems.

We report the single-crystal growth and characterization of ${\mathrm{EuIn}}_2$, a magnetic topological semimetal candidate, according to our density functional theory (DFT) calculations. We present results from electrical resistance, magnetization, Mössbauer spectroscopy, and x-ray resonant magnetic scattering (XRMS) measurements. We observe three magnetic transitions at $T_{\text{N}1}\sim 14.2\mathrm{K}, T_{\text{N}2}\sim 12.8\mathrm{K},$ and $T_{\text{N}3}\sim 11\mathrm{K}$, signatures of which are consistently seen in anisotropic temperature-dependent magnetic susceptibility and electrical resistance data. Mössbauer spectroscopy measurements on ground crystals are consistent with an incommensurate sinusoidally modulated magnetic structure below the transition at $T_{\text{N}1}\sim 14\mathrm{K}$, followed by the appearance of higher harmonics in the modulation on further cooling roughly below $T_{\text{N}2}\sim 13\mathrm{K}$ before the moment distribution squaring up below the lowest transition around $T_{\text{N}3}\sim 11\mathrm{K}$. XRMS measurements showed the appearance of magnetic Bragg peaks below $T_{\text{N}1}\sim 14\mathrm{K}$, with a propagation vector of $\mathit{\tau }=({\tau }_h,{\overline{\tau }}_h,0)$, with ${\tau }_h\mathrm{varying}$ with temperature, and showing a jump at $T_{\text{N}3}\sim 11\mathrm{K}$. The temperature dependence of ${\tau }_h$ between $\sim 11$ and 14 K shows incommensurate values consistent with the Mössbauer data. XRMS data indicate that ${\tau }_h$ remains incommensurate at low temperatures and locks into ${\tau }_h=0.3443\left(1\right)$.