We report a comprehensive study of the uniaxial stress response of charge density wave (CDW) correlations in detwinned single crystals of the high-temperature superconductor ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+x}$ (${\mathrm{YBCO}}_{6+x}$) with $0.40\le x\le 0.93$ (hole-doping levels $0.072\le p\le 0.168$) by means of Cu $L_3$-edge resonant energy-integrated x-ray scattering (REXS). We show that the influence of uniaxial stress is strongly doping dependent: the quasi-two-dimensional CDW is enhanced by in-plane uniaxial stress in a wide hole-doping range ($0.45\le x\le 0.80$), but only barely affected in the most underdoped and optimally doped samples ($x=0.40$ and 0.93), where the CDW correlation length is minimal. A stress-induced three-dimensionally long-range-ordered (3D) CDW was observed only in ${\mathrm{YBCO}}_{6.50}$ and ${\mathrm{YBCO}}_{6.67}$. The temperature dependence of the 3D CDW clearly indicates a strong competition with superconductivity. Based on the systematic strain-, doping-, and temperature-dependent REXS measurements reported here, we discuss the relationship between charge order and superconductivity in ${\mathrm{YBCO}}_{6+x}$ and other cuprates.

High-resolution angle- and spin-resolved photoemission spectroscopy (ARPES) of the triple-layered ruthenate ${\mathrm{Sr}}_4{\mathrm{Ru}}_3{\mathrm{O}}_{10}$ reveals features of the electronic structure that extend our understanding of the layered strontium ruthenates. The spectra near the Fermi energy are very different from the nonmagnetic analogues ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ and ${\mathrm{Sr}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ with distinct Fermi surfaces for wide electronlike minority spin bands around the zone center and narrow holelike majority spin Fermi surface contours around the zone corners. The most dramatic results are two narrow spectral peaks $\sim 30$ meV below the Fermi level, a spin-minority holelike band at the Brillouin zone center, and a spin-majority saddle-band van Hove singularity at the zone edge, which exhibits almost 100% spin polarization at low temperature, and a strong temperature dependent coherence-incoherence crossover attributed to Hund metal correlations. Quantitative comparison of the ARPES to spin-polarized density functional theory (DFT) calculations identify the specific antibonding and nonbonding orbital origins of the narrow bands, with a prediction of different spatial localization in the central and outer layers. This is shown to be consistent with experimental ARPES multizone matrix element intensity variations, and implicates outer-layer-specific control of the in-plane metamagnetism. The renormalization of the bands relative to the mean-field DFT, the demonstration of spin-polarized oxygen bands, and of spin-minority and spin-majority band-crossing hybridization provide a more complete picture of the magnetism which displays aspects of both delocalized and local moment behavior.

We uncover a high-field magnetic phase in $i$-MAX compounds exhibiting a canted antiferromagnetic order with unprecedented properties, revealed through NMR and AC susceptibility. Intriguingly, as the atomic number of rare earth increases, the transition field of this canted antiferromagnetic phase grows at the expense of the lower-field antiferromagnetic state. Our findings point to the complexity of the magnetic structure in $i$-MAX compounds, demonstrating a nontrivial evolution of their phase diagram while increasing both the atomic number of the rare-earth element and the external field.

The precise manipulation of the coercive field in ferroelectric materials is essential for understanding their intrinsic characteristics and broadening their practical applications. In most displacement-type ferroelectrics, the coercive field typically decreases monotonically with increasing electronic doping levels. However, the modulation of coercive fields in sliding ferroelectrics, due to their unique ferroelectric origins, remains an intriguing and unexplored territory. Here, we demonstrate that the coercive field of sliding ferroelectrics increases with higher levels of electronic doping. Using $1T^{\prime }\text{-Re}{\mathrm{S}}_2$ multilayers as a model, we show that the density of sulfur vacancies, which can be adjusted through annealing in different atmospheres, governs the extent of charge doping. Piezoresponse force microscopy measurement results reveal that an increase in sulfur vacancy density leads to a higher ferroelectric switching barrier, resulting in a coercive-field enhancement of up to 870 kV/cm. These experimental findings are corroborated by theoretical calculations. Our findings highlight the distinct features of sliding ferroelectrics compared to conventional ones, opening up avenues for innovative applications of sliding ferroelectrics.

An out-of-plane magnetic field can always suppress superconductivity. In Bernal-stacked bilayer graphene (BBG), recently observed activation of superconductivity (SC) through either in-plane magnetic fields or proximate spin-orbit coupling (SOC) offers a rare instance of switching superconductivity $\mathit{on}$. To understand this, we must first examine the nonsuperconducting state. We propose an incommensurate current density wave (CrDW) driven by Van Hove singularities away from the zone corners as a competing order. We note that the two switches, the in-plane field and the SOC, both break spin degeneracy. Our parquet renormalization group analysis reveals that breaking spin degeneracy shifts the balance from CrDW, favored under spin degeneracy, to SC when degeneracy is lifted. Driven by purely repulsive interactions, the pairing symmetry of the resulting SC is a $p/d$ wave. The presence of CrDW accounts for the nonlinear $I\text{−}V$ behavior in the normal state and suggests potential anomalous Hall effects due to time-reversal symmetry breaking. We further predict that reducing screening could enhance SC.

In the presence of an applied magnetic field, the viscosity tensor of electron flows exhibits an off-diagonal component. This Hall or odd viscosity has recently been measured in high-mobility devices. It is known that use of the hydrodynamic theory to extract the Hall viscosity from Hall resistivity measurements strongly overestimates its value. We develop a general transport theory, using a matched asymptotic expansion of the kinetic equation in the near-hydrodynamic regime, and thereby investigate the origin of this discrepancy. This reveals that bulk, near-boundary and boundary condition corrections compete with the classical Hall (odd) viscosity. This finding reconciles the above-mentioned disparity and the transport theory we report provides a basis for future measurements.

Free electrons hopping on hyperbolic lattices embedded on a negatively curved space can foster (a) Dirac liquids, (b) Fermi liquids, and (c) flat bands, respectively characterized by a vanishing, constant, and divergent density of states near the half filling. From numerical self-consistent mean-field Hartree analyses, we show that nearest-neighbor Coulomb and on-site Hubbard repulsions respectively give rise to charge-density-wave and antiferromagnetic orders featuring staggered patterns of average electronic density and magnetization in all these systems, when the hyperbolic tessellation is accomplished by periodic arrangements of even $p$-gons. Both quantum orders dynamically open mass gaps near the charge neutrality point via spontaneous symmetry breaking. Only on hyperbolic Dirac materials these orderings take place via quantum phase transitions (QPTs) beyond critical interactions, which however decrease with increasing curvature, showcasing curvature-induced weak-coupling QPTs. We present scaling of these masses with the corresponding interaction strengths.

The detection of ultrastrong coherent light-matter interaction by photocurrent measurements was realized recently, which provides new ways for investigating polariton physics and quantum transport in cavity fields. The physical processes underlying this electrical detection method, however, have not yet been fully understood. In particular, the properties and origins of the photocurrent in the ultrastrong coupling regime remain elusive. In this work, we have investigated the terahertz-induced photocurrent in a coupled system of the quantum Hall edge electrons and terahertz photons in a split ring resonator. The energy dispersion of the coupled system was measured by conducting terahertz-induced photocurrent spectroscopy through a quantum point contact (QPC). The dependence of the terahertz photocurrent on the polarities of a source-drain bias voltage and a magnetic field was systematically measured. We have found that the observed photocurrent is chiral in nature, showing that the behavior of the photocurrent is consistent with nonequilibrium edge channel transport due to the generation and relaxation of Landau polaritons in multiple Landau levels. Furthermore, we point out that the QPC serves as an enhancer for the photocurrent signals.

Inspired by twisted bilayer graphene, artificial moiré superlattices of classical waves have been attracting tremendous interest. Here, we report experimental observation of ultraflat bands in acoustic moiré metamaterials with frequency-momentum spectra, accompanying a real-space visualization of the hallmark localized states. Strikingly different from the established magic angle mechanism for twisted bilayer graphene, the ultraflat bands are formed by weakly coupled moiré potential-well states inside a wide band gap, and can be realized over a broad range of twist angles. Our findings, applicable to all artificial crystals, enable new possibilities for manipulating classical waves with moiré structures.

Certain pure-state symmetry-protected topological orders (SPT) can be used as a resource for transmitting quantum information. Here we investigate the ability to transmit quantum information using decohered SPT states and relate this property to the “strange correlation functions” which diagnose quantum many-body orders in these mixed states. This perspective leads to the identification of a class of quantum channels—termed symmetry-decoupling channels—which do not necessarily preserve any weak or strong symmetries of the SPT state but nevertheless protect quantum many-body order in the decohered mixed state. We quantify the ability to transmit quantum information in decohered SPT states through the coherent quantum information, whose behavior is generally related to a decoding problem, whereby local measurements in the system are used to attempt to “learn” the symmetry charge of the SPT state before decoherence.

Temperature-dependent harmonic approximations generalize the ground-state phonon picture, and have found widespread use in computing the thermal properties of materials. However, applying these approaches to access the thermal conductivity still lacks a formal justification, in particular due to the use of perturbation theory. In this work, we derive a theory of heat transport in anharmonic crystals, using the mode-coupling theory of anharmonic lattice dynamics. Starting from the Green-Kubo formula, we develop the thermal conductivity tensor based on the system's dynamical susceptibility, or spectral function. Our results account for both the diagonal and off-diagonal contributions of the heat current, with and without collective effects. We implement our theory in the temperature-dependent effective potential (tdep) package, and have notably introduced a Monte Carlo scheme to compute phonon scattering due to third- and fourth-order interactions, achieving a substantial reduction in computational cost which enables full convergence of such calculations. We apply our methodology to systems with varying regimes of anharmonicity and thermal conductivity to demonstrate its universality. These applications highlight the importance of the phonon renormalizations, and their interactions beyond the harmonic order. Overall, our work advances the understanding of thermal conductivity in anharmonic crystals and provides a theoretically robust framework for predicting heat transport in complex materials.

We present the results of muon-spin relaxation (${\mu }^{+}\mathrm{SR}$) measurements of the van der Waals magnet ${\mathrm{NiI}}_2$, which probe magnetic phase transitions at $T_{\mathrm{N}1}=73\mathrm{K}$ and $T_{\mathrm{N}2}=62\mathrm{K}$. Supporting density functional theory (DFT) calculations allow the determination of a single muon stopping site whose magnetic environment is consistent with the proposed ground-state magnetic structure. ${\mu }^{+}\mathrm{SR}$ measurements of the dynamics reveal behavior consistent with spin-wave excitations below $T_{\mathrm{N}2}$. In the region $T_{\mathrm{N}2}<T<T_{\mathrm{N}1}$ the character of the dynamics changes qualitatively, resulting in an unusual region of temperature-independent fluctuations.

One of the key elements in spintronics research is the spin Hall effect, allowing to generate spin currents from charge currents. A large spin Hall effect is observed in materials with strong spin-orbit coupling, e.g., Pt. Recent research suggests the existence of an orbital Hall effect, the orbital analog to the spin Hall effect, which also arises in weakly spin-orbit-coupled materials like Ti, Mn, or Cr. In Pt both effects are predicted to coexist. In any of these materials, a magnetic field perpendicular to the spin or orbital accumulation leads to additional Hanle dephasing and thereby the Hanle magnetoresistance (MR). To reveal the MR behavior of a material with both spin and orbital Hall effect, we first study the MR of Pt thin films over a wide range of thicknesses. Careful evaluation shows that the MR of our textured samples is dominated by the ordinary MR rather than by the Hanle effect. We analyze the intrinsic properties of Pt films deposited by different groups and show that next to the resistivity also the structural properties of the film influence which MR dominates. We further show that this correlation can be found in both spin Hall active materials like Pt and orbital Hall active materials, like Ti. For both materials, we find a large Hanle MR for the samples without apparent structural order, whereas the ordinary MR dominates in the crystalline samples. We then provide a set of rules to distinguish between the ordinary and the Hanle MR. We suggest that in all materials with a spin or orbital Hall effect the Hanle MR and the ordinary MR coexist and the purity, crystallinity, and electronic structure of the thin film determine the dominating effect.

As topological solitons in real space, magnetic (M)/electric (E) skyrmions have attracted enduring attention due to their significant roles in both fundamental science and potential information-related applications. However, it remains challenging to effectively track/manipulate M skyrmions via energy-saving routes. Besides, the stability of E skyrmions usually require harsher conditions than their M counterparts. Here, a strategy so-called magnetoelectric imprint is proposed to overcome these obstacles. Through proximate interactions, an isoperiodic bijection is established between the local dipoles and spin moments. Thus, M skyrmions can be mapped into E skyrmions, which provides an alternative strategy to detect/manipulate M skyrmions by recognizing/controlling their E fingerprints. More interestingly, these magnetism induced E skyrmions come from the distortions of electron clouds instead of lattice, which provides an inborn superior for ultra-high-speed dynamics. Our work goes beyond the conventional separating territories of M/E skyrmions by demonstrating an emerging quasiparticle, i.e., the ME skyrmions, thus opens one more route to realize magnetoelectric functions in low-dimensional materials.

Unusual successive order in ${\mathrm{NdB}}_4$ with the frustrated Shastry-Sutherland lattice was investigated by means of inelastic neutron scattering. We found that the pseudoquartet with $|\pm 5/2\rangle$ and $|\pm 7/2\rangle$ in the paramagnetic state splits into four levels in the magnetically ordered states. The observed spectra are in good agreement with the $f$-electron states obtained from the on-site Hamiltonian with the magnetic interaction $\langle J_x\rangle J_x$, the coupling of $J_x$ with quadrupole $O_{zx}$, and the crystalline electric field potential. The $f$-electron states reproduce the temperature dependences of the in-plane moment $m_{\perp }=\langle J_x\rangle$, which is the primary order parameter, and a weakly induced $m_c=\langle J_z\rangle$ as the secondary order parameter. The magnetic-quadrupole coupling emerges and plays an essential role under the geometrical frustration, where the Heisenberg interactions are canceled out.

We develop a Green's function approach for the nonequilibrium dynamics of multilevel quantum dots coupled to multiple fermionic reservoirs in the presence of a bosonic environment. Our theory is simpler than the Keldysh approach and goes beyond scattering state constructions. In concrete terms, we study Josephson junctions containing a quantum dot and coupled to an electromagnetic environment. In the dot region, spin-orbit interactions, a Zeeman field, and in principle Coulomb interactions can also be included. We then study quantum Mpemba effects, assuming that the average phase difference across the Josephson junction is subject to a rapid quench. For a short single-channel junction, we show that both types of quantum Mpemba effects allowed in open quantum systems can occur. We also study an intermediate-length junction, where spin-orbit interactions and a Zeeman field are included. Again quantum Mpemba effects are predicted.

The experimental measurement of collective charge fluctuations in metals and superconductors is a preferential tool to benchmark fundamental interactions in solids. Recent experiments in multicomponent systems, from superconducting layered cuprates to multiband metals, highlighted striking effects due to the interplay between different degrees of freedom. In this paper we provide a physical explanation for the existence of a “ghost” Josephson plasmon in bilayer superconductors, layered systems with two layers per unit cells that interact with two different Josephson couplings. We show that one of the two plasmons that emerge after the breaking of the translational symmetry along the out-of-plane direction is connected to counterflowing current fluctuations polarized perpendicularly to the planes. This effect makes it a staggered mode that is virtually transverse at small out-of-plane momenta $q_c$, explaining why it is hidden in the density response at small $q_c$. Our work offers an additional perspective on the understanding of collective excitations in systems with multiple intertwined degrees of freedom.

We theoretically derive the sum rule for the negative first moment of the absorptive optical conductivity with excitonic effects and establish its connection to the quantum weight $K$ and Chern number $C$ of the ground state. Applying this framework, we investigate the excitonic optical response of the Chern insulator at a hole filling factor $\nu =1$ in twisted bilayer ${\mathrm{MoTe}}_2$. A single chiral exciton state, which selectively absorbs circularly polarized light of a specific handedness, dominates the optical sum rule. The chiral exciton state comprises two types of interlayer electron-hole transitions, which cancel out the total out-of-plane dipole moment. The absorption spectrum shows nearly perfect magnetic circular dichroism, which can be attributed to the nearly saturated bound $K\ge \left|C\right|$ of the Chern insulator under study. Our work illustrates the potential of using excitonic optical responses to probe quantum geometry encoded by $K$ and $C$ of Chern insulators in moiré superlattices.

Electron shuttling is one of the current avenues being pursued to scale semiconductor quantum dot-based spin qubits. Adiabatic spin qubit transfer along a chain of tunnel-coupled quantum dots is one of the possible schemes. In this scheme, we theoretically analyze the dephasing of a spin qubit that is adiabatically transferred between two tunnel-coupled quantum dots. We focus on the regime where the Zeeman splitting is lower than the tunnel coupling, such that interdot tunneling with spin flip is absent. We analyze the sources of errors in spin-coherent electron transfer for Si- and GaAs-based quantum dots. In addition to the obvious effect of fluctuations in spin splitting within each dot, leading to finite $T_2^{*}$ for the stationary spin qubit, we consider the effects activated by detuning sweeps: failure of charge transfer due to charge noise and phonons, spin relaxation due to the enhancement of spin-orbit mixing at the tunnel-induced anticrossing of states localized in the two dots, and spin dephasing caused by low- and high-frequency noise coupling to the electron's charge. We show that the latter effect is activated by differences in Zeeman splittings between the two dots. Importantly, all the error mechanisms are more dangerous at low tunnel couplings. Our results indicate that away from micromagnets, maximizing the fidelity of coherent transfer aligns with minimizing charge transfer error that was previously considered in Krzywda and Cywiński [Phys. Rev. B 104, 075439 (2021)]. For silicon, we suggest having tunnel coupling fulfilling $2t_c\gtrsim 60\mu \mathrm{eV}$ when one aims to coherently transfer a spin qubit across a $\sim 10\mu \mathrm{m}$ long array of $\sim 100$ quantum dots with error less than ${10}^{-3}$.

Understanding the interplay between the thermodynamics and kinetics of phase transition under high pressure is a current challenge in material and physical sciences. Here, we present the structural response of anatase ${\mathrm{TiO}}_2$ up to 20 GPa and over compression rates ranging from 0.03 to 3.61 GPa/s, using a piezo-driven dynamic diamond anvil cell coupled with time-resolved Raman spectroscopy. It is found that the phase evolution of anatase ${\mathrm{TiO}}_2$ follows the expected thermodynamics path (i.e., $\mathrm{anatase}\to \alpha \text{−}{\mathrm{PbO}}_2\to \text{baddeleyite}$) regardless of the applied compression rate, however, the formation conditions of high pressure phases are kinetically controlled. Both phase boundaries increase approximately linearly with the logarithm of compression rate, that seems to resolve apparent contradictions between previous high pressure results. We ascribe these to the sluggish transition kinetics of a typical reconstructive transition mechanism, and highlight that the compression rate behaves as the third dimension within a high pressure phase diagram.