The ground state of metamagnetic materials can be controlled by magnetic field, promising new functionalities for spintronics applications. Yet, a microscopic understanding of the interplay of the electronic structure with the susceptibility to emergent orders is often missing, but would greatly facilitate optimization of the properties of metamagnetic materials. Here, we use low-temperature scanning tunneling microscopy (STM) and spectroscopy to study the metamagnetism in the trilayer ruthenate ${\mathrm{Sr}}_4{\mathrm{Ru}}_3{\mathrm{O}}_{10}$, combining STM-based magnetostriction measurements with quasiparticle-interference imaging (QPI) to elucidate the role of the microscopic electronic structure in the macroscopic metamagnetic properties. Our results highlight the importance of the orthorhombicity of the material for its metamagnetic properties, confirmed by magnetization measurements. Our QPI results show clear signatures of the minority spin bands crossing the Fermi energy and provide a link among the ferromagnetic properties, spin-orbit coupling, and the orthorhombicity of the crystal structure.

The recently discovered layered kagome metals $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ ($A=\mathrm{K}$, Rb, Cs) have attracted much attention because of their unique combination of superconductivity, charge density wave (CDW) order, and nontrivial band topology. The CDW order with an in-plane $2\times 2$ reconstruction is found to exhibit exotic properties, such as time-reversal symmetry breaking and rotational symmetry breaking. However, the nature of the CDW, including its dimensionality, structural pattern, and effect on electronic structure, remains elusive despite intense research efforts. Here, we present a comprehensive study on the electronic structure of $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ by combining polarization- and temperature-dependent angle-resolved photoemission spectroscopy with density-functional theory calculations. Apart from the energy shift of van Hove singularities, we observe double-band splittings for V $d$-orbital bands in the CDW phase, which provide essential information for revealing the dimensionality and pattern of the CDW order. Our calculations show that three-dimensional CDW orders containing stacking of star-of-David and trihexagonal patterns along the $c$ axis can quantitatively reproduce the experimental features. The characteristic splittings from the two patterns can be experimentally extracted and they are quantitatively consistent with calculations, clearly demonstrating intrinsic coexistence of the two patterns in the CDW order. These results provide crucial insights into the nature and distortion pattern of the CDW order, and its signature in the electronic structure, thereby laying down the basis for a substantiated understanding of the exotic properties in the family of $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ kagome metals.

We report gate-induced enhancement of intrinsic charge rectification without p-n junctions in chiral semiconductor Te under magnetic field $B$. As gating shifts the chemical potential to the valence band maximum of Te, the charge rectification efficiency is enhanced hundredfold. By integrating model calculations, we attribute the charge rectification to the $B$-induced asymmetry of the chiral band structure. We also show that the carrier density subject to this asymmetry is augmented by a saddle-point structure near the valence band maximum, which further enhances the gate-tunable charge rectification together with its improved switchability and thermal robustness.

The charge character of Andreev bound states (ABSs) in a three-terminal semiconductor-superconductor hybrid nanowire was measured using local and nonlocal tunneling spectroscopy. The device is fabricated using an epitaxial InAs/Al two-dimensional heterostructure with several gate-defined side probes. ABSs give rise to distinct local and nonlocal conductance signatures which evolve as a function of magnetic field and gate voltage. At high magnetic fields, ABSs are found to oscillate around zero as a function of gate voltage, with modifications of their charge consistent with expectations for the total Bardeen-Cooper-Schrieffer charge of ABSs.

We develop solvable models of large-$N$ hybrid quantum circuits on qubits and fermions with tunable long-range power-law interactions and continuous local monitoring. These models provide analytical access to the entanglement phase diagram and error-correcting properties of many-body entangled nonequilibrium states generated by such dynamics. In one dimension, the long-range couplings are irrelevant for $\alpha >3/2$, where $\alpha$ is the power-law exponent, and the models exhibit a conventional measurement-induced phase transition between volume- and area-law entangled phases. For $1/2<\alpha <3/2$, the long-range couplings become relevant, leading to a nontrivial dynamical exponent at the measurement-induced phase transition. More interestingly, for $\alpha <1$, the entanglement pattern receives a subvolume correction for both area-law and volume-law phases, indicating that the phase realizes a quantum error correcting code whose code distance scales as $L^{2-2\alpha }$. While the entanglement phase diagram is the same for both the interacting qubit and fermionic hybrid Brownian circuits, we find that long-range free-fermionic circuits exhibit a distinct phase diagram with two different fractal entangled phases.

The orbital occupancy, as the origin of Hund's rule coupling, provides critical information in understanding the multiorbital iron-based superconductors. The one-unit-cell (1UC) FeSe thin film on a ${\mathrm{SrTiO}}_3$ substrate with superconductive $T_{\mathrm{c}}$ above 60 K has been reported with unique electronic structures as well as orbital occupancy. In this paper, we present the x-ray absorption spectroscopy and resonant inelastic x-ray scattering (RIXS) study of the FeSe/STO thin films of different thicknesses. Together with the atomic multiplet simulation analysis, the FeSe/STO thin films (from 1UC to 10UC) are shown with the pure $3d6$ electronic configuration which is identical to the bulk FeSe. Moreover, 1UC FeSe/STO is found to be distinctively more persistent in hosting the $3d6$ configuration other than the thicker films under the oxidization process. The robustness of the $3d6$ in 1UC FeSe/STO is discussed as a result of charge transfer from the substrate, as well as a mechanism to maintain the high-$T_{\mathrm{c}}$ superconductivity. Finally, our research calls for a further high-resolution RIXS study of the pristine superconductive 1UC FeSe/STO thin film.

We theoretically study photocurrents in metals that break both inversion $\mathcal{P}$ and time reversal $\mathcal{T}$ symmetries within the transparent region. We find that the system under the ac electric fields is well described with an effective Hamiltonian and the photocurrent is of the order of $O({\omega }_J/\gamma )$ if the frequency of the induced current ${\omega }_J$ and the scattering rate $\gamma$ satisfy ${\omega }_J/\gamma \ll 1$, and vanishes in the limit of ${\omega }_J/\gamma \to 0$. On the other hand, the effective Hamiltonian description indicates that nonvanishing photocurrent can appear even in the transparent region if the system is thin enough compared to the mean-free path in the direction of the induced current (where $\gamma$ can be effectively regarded as 0). Candidate materials for the such photovoltaic effect within the transparent region include conducting multiferroics breaking both $\mathcal{P}$ and $\mathcal{T}$ symmetries.

It was demonstrated recently that on ultrashort timescales magnetization dynamics not only exhibits precession but also nutation. Here, we investigate how nutation can contribute to spin switching, leading towards ultrafast data writing. We use analytic theory and numerical spin simulations to discuss the behavior of ferromagnets and antiferromagnets in high-frequency magnetic fields. In ferromagnets, linearly polarized fields align the magnetization perpendicular to the external field, enabling ${90}^{\circ }$ switching. For circularly polarized fields in the $xy$ plane, the magnetization tilts to the $z$ direction. During this tilting it rotates around the $z$ axis, allowing ${180}^{\circ }$ switching. In antiferromagnets, external fields with frequencies higher than the nutation frequency align the order parameter parallel to the field direction, while for lower frequencies it is oriented perpendicular to the field. The switching frequency increases with the magnetic field strength, and it deviates from the Larmor frequency, making it possible to outpace precessional switching in high magnetic fields.

We present algorithmic and implementation details for the fully self-consistent finite-temperature $GW$ method in Gaussian Bloch orbitals for solids. Our implementation is based on the finite-temperature Green's function formalism in which all equations are solved on the imaginary axis, without resorting to analytical continuation during the self-consistency. No quasiparticle approximation is employed and all matrix elements of the self-energy are explicitly evaluated. The method is tested by evaluating the band gaps of selected semiconductors and insulators. We show agreement with other, differently formulated, finite-temperature $\mathrm{sc}GW$ implementations when finite-size corrections and basis-set errors are taken into account. By migrating computationally intensive calculations to graphics processing units, we obtain scalable results on large supercomputers with nearly optimal performance. Our work demonstrates the applicability of Gaussian orbital based $\mathrm{sc}GW$ for ab initio correlated material simulations and provides a sound starting point for embedding methods built on top of $GW$.

We report on the theoretical and experimental investigation of valley-selective optical Stark and Bloch-Siegert shifts of exciton resonances in monolayers ${\mathrm{WSe}}_2$ and ${\mathrm{MoS}}_2$ induced by strong circularly polarized nonresonant optical fields. We predict and observe transient shifts of both 1sA and 1sB exciton transitions in the linear interaction regime. The theoretical description is based on semiconductor Bloch equations. The solutions of the equations are obtained with a modified perturbation technique, which takes into account many-body Coulomb interaction effects. These solutions allow to explain the polarization dependence of the shifts and calculate their values analytically. We found experimentally the limits of the applicability of the theoretical description by observing the transient exciton spectra change at high field amplitudes of the driving wave.

High-field charge transport in semiconductors is of fundamental interest and practical importance. While the ab initio treatment of low-field transport is well developed, the treatment of high-field transport is much less so, particularly for multiphonon processes that are reported to be relevant in GaAs. Here, we report a calculation of the high-field transport properties and current power spectral density (PSD) of hot electrons in GaAs from first principles including on-shell two-phonon (2ph) scattering. The on-shell 2ph scattering rates are found to qualitatively alter the high-field distribution function by increasing both the momentum and energy relaxation rates as well as contributing markedly to intervalley scattering. This finding reconciles a long-standing discrepancy regarding the strength of intervalley scattering in GaAs as inferred from transport and optical studies. The characteristic nonmonotonic trend of PSD with electric field is not predicted at this level of theory. Our work shows how ab initio calculations of high-field transport and noise may be used as a stringent test of the electron-phonon interaction in semiconductors.

We investigate the computational power of the recently introduced class of isometric tensor network states (isoTNSs), which generalizes the isometric conditions of the canonical form of one-dimensional matrix-product states to tensor networks in higher dimensions. We discuss several technical details regarding the implementation of isoTNSs-based algorithms and compare different disentanglers—which are essential for an efficient handling of isoTNSs. We then revisit the time evolving block decimation for isoTNSs $\left({\text{TEBD}}^2\right)$ and explore its power for real-time evolution of two-dimensional (2D) lattice systems. Moreover, we introduce a density matrix renormalization group algorithm for isoTNSs $\left({\text{DMRG}}^2\right)$ that allows to variationally find ground states of 2D lattice systems. As a demonstration and benchmark, we compute the dynamical spin structure factor of 2D quantum spin systems for two paradigmatic models: First, we compare our results for the transverse field Ising model on a square lattice with the prediction of the spin-wave theory. Second, we consider the Kitaev model on the honeycomb lattice and compare it to the result from the exact solution.

Argon is the most abundant noble gas on Earth and its noble, atomic fluid nature makes it an excellent candidate for comparison of experiment and theory at extreme conditions. We performed a combined computational and experimental study on shock compressed cryogenic liquid argon. Using Sandia's Z machine, we shock compressed liquid argon to 600 GPa and reshock states up to 950 GPa. Laser shock experiments at the Omega Laser facility extend the principal Hugoniot to 1000 GPa and provided temperature data along the principal Hugoniot. The plate impact experiments and laser shock experiments used well-characterized impedance matching standards and demonstrate consistent results between the two platforms over a common range. Density functional theory based molecular dynamics simulations provided additional data on the Hugoniot to 600 GPa. The combined experimental data and simulation results provide constraints on the development of new equation of state models at extreme conditions.

${\text{Fe}}_{3-x}{\text{GeTe}}_2$ is a layered magnetic van der Waals material of interest for both fundamental and applied research. Despite the observation of intriguing physical properties, open questions exist even on the basic features related to magnetism: is it a simple ferromagnet or are there antiferromagnetic regimes, and are the moments local or itinerant. Here, we demonstrate that antiferromagnetic spin fluctuations coexist with the ferromagnetism through comprehensive elastic and inelastic neutron scattering and thermodynamic measurements. Our realistic dynamical mean-field theory calculations reveal that the competing magnetic fluctuations are driven by an orbital selective Mott transition (OSMT), where only the plane-perpendicular $a_{1g}$ orbital of the $\mathrm{Fe}\left(3d\right)$ manifold remains itinerant. Our results highlight the multi-orbital character in ${\text{Fe}}_{3-x}{\text{GeTe}}_2$ that supports a rare coexistence of local and itinerant physics within this material.

With the evidence of intervalley attraction-mediated by phonon or topological fluctuations, we assume the intervalley attraction and aim at identifying universal properties of moiré flat bands that shall emerge. We show that by matching the interaction strength of intervalley attraction with intravalley repulsion, the flat-band limit becomes exactly solvable. Away from the flat-band limit, the system can be simulated via quantum Monte Carlo (QMC) methods without sign problem for any fillings. Combining analytic solutions with large-scale numerical simulations, we show that upon increasing temperature, the superconducting phase melts into a bosonic fluid of Cooper pairs with large/diverging compressibility. In contrast to flat-band attractive Hubbard models, where similar effects arise only for on-site interactions, our study indicates this physics is a universal property of moiré flat bands, regardless of microscopic details such as the range of interactions and/or spin-orbit couplings. At higher temperature, the boson fluid phase gives its way to a pseudogap phase, where some Cooper pairs are torn apart by thermal fluctuations, resulting in fermion density of states inside the gap. Unlike the superconducting transition temperature, which is very sensitive to doping and twisting angles, the gap and the temperature scale of the boson fluid phase and the pseudogap phase are found to be nearly independent of doping level and/or flat-band bandwidth. The relevance of these phases with experimental discoveries in the flat-band quantum moiré materials is discussed.

In conventional Bardeen-Cooper-Schrieffer superconductors, Cooper pairs of electrons of opposite spin (i.e., singlet structure) form the ground state. Equal-spin triplet pairs (ESTPs), as in superfluid ${}^3\mathrm{He}$, are of great interest for superconducting spintronics and topological superconductivity, yet remain elusive. Recently, odd-parity ESTPs were predicted to arise in (few-)monolayer superconducting ${\mathrm{NbSe}}_2$, from the noncollinearity between the out-of-plane Ising spin-orbit field (due to the lack of inversion symmetry in monolayer ${\mathrm{NbSe}}_2$) and an applied in-plane magnetic field. These ESTPs couple to the singlet order parameter at finite field. Using van der Waals tunnel junctions, we perform spectroscopy of superconducting ${\mathrm{NbSe}}_2$ flakes, of 2–25 monolayer thickness, measuring the quasiparticle density of states (DOS) as a function of applied in-plane magnetic field up to 33 T. In flakes $\lesssim 15$ monolayers thick the DOS has a single superconducting gap. In these thin samples, the magnetic field acts primarily on the spin (vs orbital) degree of freedom of the electrons, and superconductivity is further protected by the Ising field. The superconducting energy gap, extracted from our tunneling spectra, decreases as a function of the applied magnetic field. However, in bilayer ${\mathrm{NbSe}}_2$, close to the critical field (up to 30 T, much larger than the Pauli limit), superconductivity appears to be more robust than expected from Ising protection alone. Our data can be explained by the above-mentioned ESTPs.

It is well known that many topological phase transitions of intrinsic Abelian topological phases are accompanied by condensation and confinement of anyons. However, for non-Abelian topological phases, more intricate phenomena can occur at their phase transitions, because the multiple degenerate degrees of freedom of a non-Abelian anyon can change in different ways after phase transitions. In this paper, we study these new phenomena, including partial condensation, partial deconfinement, and especially anyon splitting (a non-Abelian anyon splits into different kinds of the new anyon species) using projected entangled pair states (PEPS). First, we show that anyon splitting can be observed from the topologically degenerate ground states. Next, we construct a set of PEPS describing all possible degrees of freedom of the same non-Abelian anyon. From the overlaps of this set of PEPS of a given non-Abelian anyon with the ground state, we can extract the information of partial condensation. Then, we construct a central object, a matrix defined by the norms and overlaps among the PEPS in that set. The information of partial deconfinement can be extracted from this matrix. In particular, we use it to construct an order parameter which can directly detect anyon splitting. We demonstrate the power of our approach by applying it to a range of non-Abelian topological phase transitions: From $D\left(S_3\right)$ quantum double to toric code, from $D\left(S_3\right)$ quantum double to $D\left(Z_3\right)$ quantum double, from $\mathrm{Rep}\left(S_3\right)$ string-net to toric code, and finally from double Ising string-net to toric code.

We theoretically investigate the dynamics of two spin qubits interacting with a magnetic medium. A systematic formal framework for this qubit-magnet hybrid system is developed in terms of the steady-state properties of the magnetic medium. Focusing on the induced dissipative coupling between the spin qubits, we show how a sizable long-lived entanglement can be established via the magnetic environment, in the absence of any coherent coupling. Moreover, we demonstrate that maximally entangled two-qubit states (Bell states) can be achieved in this scheme when complemented by proper postselection. In this situation, the time evolution of the entanglement is governed by a non-Hermitian Hamiltonian, where dynamical phases are separated by an exceptional point. The resultant Bell state is robust against weak random perturbations and does not require the preparation of a particular initial state. Our study may find applications in quantum information science, quantum spintronics, and for sensing of nonlocal quantum correlations.

We study the high-energy phase diagram of a two-dimensional spin-$\frac{1}{2}$ Heisenberg model on a square lattice in the presence of either quenched or quasiperiodic disorder. The use of large-scale tensor network numerics allows us to compute the bipartite entanglement entropy for systems of up to $60\times 7$ lattice sites. We provide evidence for the existence of a many-body localized regime for large disorder strength that features an area law in excited states and that violates the eigenstate thermalization hypothesis. From a finite-size analysis, we determine an estimate for the critical disorder strength where the transition to the ergodic regime occurs in the quenched case.

We present a unified framework to construct and classify topological crystalline superconductors (TCSCs). The building blocks are one-dimensional topological superconductors (TSCs) protected solely by on-site symmetries, which are arranged and glued by crystalline symmetries in real space. We call this real-space scheme “wire construction”, and we show its procedure can be formulated mathematically. For illustration, we treat TCSCs of Altland-Zirnbauer (AZ) class DIII protected by wallpaper group as well as layer group symmetries, with the resulting states by wire construction being TCSCs in two dimension. We also discuss how these real-space TCSCs by wire construction are characterized by anomalous boundary states. Our method provides a real-space picture for TCSCs versus momentum-space pictures.