Electronic ordering is prevalent in correlated systems, which commonly exhibit competing interactions. Here, we use x-ray diffraction to demonstrate a cascade of pressure-induced order-disorder transformations, with propagation vectors ${\mathbf{q}}_{\mathrm{CDW}}=\left(\frac{1}{2}0\frac{1}{2}\right), {\mathbf{q}}^{*}=\left(\frac{1}{3}\frac{1}{3}\frac{1}{2}\right)$, and ${\mathbf{q}}^{†}=\left(\frac{1}{3}\frac{1}{3}\frac{1}{3}\right)$, in the kagome metal FeGe. In the pressure interval between $4<p<10$ GPa, ${\mathbf{q}}_{\mathrm{CDW}}$ and ${\mathbf{q}}^{*}$ coexist and the spatial extent of the $\sqrt{3}\times \sqrt{3}$ order is nearly long range at $\sim 15$ GPa, $\sim 30$ unit cells. Above $\sim 25$ GPa, the periodic lattice distortion has a propagation wave vector of ${\mathbf{q}}^{†}=\left(\frac{1}{3}\frac{1}{3}\frac{1}{3}\right)$ at room temperature. The cascade of phase transitions is captured by the Ising model of frustrated triangular lattices and modeled by Monte Carlo simulations based on the dimerization of trigonal ${\mathrm{Ge}}_1$. The pressure dependence of the integrated intensities and correlation lengths of ${\mathbf{q}}_{\mathrm{CDW}}, {\mathbf{q}}^{*}$, and ${\mathbf{q}}^{†}$ demonstrating a competition between the $2\times 2$ and $\sqrt{3}\times \sqrt{3}$ phases prove the tunability of order-disorder phase transitions under pressure and the rich landscape of metastable/fragile phases of FeGe.

We report the synthesis of single crystals of the $R_3{\mathrm{Ni}}_{30}{\mathrm{B}}_{10}$ $(R=\mathrm{La},\mathrm{Ce})$ system which realizes the tetragonal $P4/nmm$ (No. 129) space group. We performed single crystal, transmission x-ray diffraction measurements to determine the crystal structure. Additionally, we characterized the samples through magnetization, resistivity, and heat capacity measurements. The $R=\mathrm{Ce}$ system exhibits mixed-valence states and we observe maxima in the heat capacity at $T_1^{*}=6\text{K}$ and $T_2^{*}=2\text{K}$ (both absent for $R=\mathrm{La}$) with no corresponding features in the resistivity or magnetization. We discuss the potential roles of multipolar and short-ranged/partial order in connection to the $T_1^{*}$ anomalous order.

We investigate the electrical transport properties of a magnetic kagome metal ${\mathrm{EuTi}}_3{\mathrm{Bi}}_4$, which undergoes magnetic ordering below $T_{\mathrm{C}}=10.5$ K. Unlike typical magnets showing intriguing magnetotransport in their ordered states, ${\mathrm{EuTi}}_3{\mathrm{Bi}}_4$ exhibits unusual magnetotransport behaviors in its paramagnetic phase. Specifically, the magnetoconductivity shows a linear dependence on the magnetic field at low fields below $\sim 1\mathrm{T}$, and the Hall conductivity undergoes a sign change below about 2 T. These complex magnetotransport behaviors resemble those observed in the charge density wave (CDW) phase of kagome metals $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ $(A=\mathrm{K},\mathrm{Rb},\mathrm{Cs})$. The complex magnetotransport in $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ has commonly been attributed to the possible emergence of a time-reversal symmetry-breaking chiral CDW order. However, given the absence of CDW in ${\mathrm{EuTi}}_3{\mathrm{Bi}}_4$ and its manifestation exclusively in the paramagnetic state, the complex magnetotransport observed in ${\mathrm{EuTi}}_3{\mathrm{Bi}}_4$ is likely associated with multiband transport and/or the van Hove singularities near the Fermi level.

A diluted non-Kramers doublet system ${\mathrm{Y}}_{1-x}{\mathrm{Pr}}_x{\mathrm{Ir}}_2{\mathrm{Zn}}_{20}$ is a promising candidate for exhibiting a single-site quadrupolar (two-channel) Kondo effect. We have measured the temperature-dependent magnetization of a sample for $x=0.028$ down to 0.1 K at various constant magnetic fields to extract the characteristic behaviors due to the quadrupolar Kondo effect. The Curie-Weiss fit to the magnetic susceptibility between 50 and 300 K yields a negative paramagnetic Curie temperature of $-7.0$ K, indicative of on-site antiferromagnetic interaction. The magnetization divided by the magnetic field, $M\left(T\right)/B$, at $B=0.5$ T is saturated to a constant value below 3 K. On the contrary, in higher magnetic fields of $B=1$ and 2 T, $M\left(T\right)/B$ exhibits $-\ln T$ dependence from 1 to 0.1 K, which temperature dependence is consistent with that of the quadrupolar susceptibility detected from ultrasonic measurements. The $-\ln T$ form of $M\left(T\right)/B$ appears to reflect the behavior of quadrupolar susceptibility, through the magnetic-field-induced magnetic moment due to the mixing of the non-Kramers doublet and crystalline-electric-field excited states of ${\mathrm{Pr}}^{3+}$. In $B=4$ T, $M\left(T\right)/B$ approaches a constant on cooling below 0.3 K because of the quenching of the quadrupoles in the field-induced singlet ground state.

This study presents a comprehensive and innovative exploration of how the surface potential energy landscape influences meander formation. Using the vicinal cellular automaton model, which distinguishes surface diffusion from adatom incorporation into the crystal, the research delves into various factors affecting surface pattern dynamics. By isolating the diffusion process within a defined energy potential, the study provides a detailed analysis of how changes in the potential energy well and the barrier at the top of the step contribute to meander formation. Remarkably, the results reveal that the mere presence of a potential well at the step's bottom is sufficient to induce meandering. The role of the Ehrlich-Schwoebel barrier on formed meanders is further investigated, and a mechanism for meander formation is proposed to clarify this process. The derived relation successfully reflects the wavelength of the meandered patterns observed in the simulations, emphasizing its reliability. Overall, the results highlight the essential role of the surface energy potential's landscape in governing surface pattern formation.

The shift current responses of two-dimensional systems in the gapless limit are investigated. As the energy gap becomes smaller, the interband transition probability becomes larger at the band edges. We find the divergence of the shift current response in a manner proportional to the inverse of the gap size when the system becomes a two-dimensional Weyl semimetal in the gapless limit. This behavior is different from that for electric polarization, which remains finite and has a jump across the gapless limit. It means that the quantitative relationship between electric polarizations and shift currents is broken in this gapless limit.

We examine the bulk electronic structure of ${\mathrm{Nd}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ using Ni $2p$ core-level hard x-ray photoemission spectroscopy combined with density functional theory $+$ dynamical mean-field theory. Our results reveal a large deviation of the Ni $3d$ occupation from the formal ${\mathrm{Ni}}^{2.5+}$ valency, highlighting the importance of the charge transfer from oxygen ligands. We find that the dominant $d^8$ configuration is accompanied by nearly equal contributions from $d^7$ and $d^9$ states, exhibiting an unusual valence state among Ni-based oxides. Finally, we discuss the Ni $d_{x^2-y^2}$ and $d_{z^2}$ orbital-dependent hybridization, correlation and local spin dynamics.

We quantitatively identify the multiple distinct microscopic mechanisms contributing to effective interlayer couplings (EICs) by performing first-principle calculations for two prototype superconducting cuprate families, pristine and doped ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCuO}}_2{\mathrm{O}}_{8+x}$ and ${\mathrm{Pr}}_x{\mathrm{Y}}_{1-x}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$. The major mechanisms are mediated by interlayer oxygen $p_{\sigma }\text{−}{p}_{\sigma }$ and $p_z\text{−}{p}_z$ hoppings as well as interlayer copper $d_{3z^2-r^2}$-oxygen $p_{\sigma }$ hoppings. Furthermore, we show how EICs are closely related to structural distortions such as layer bucklings and bond length changes. This allows us to provide analytical formulas that permit direct estimation of the key interatomic hoppings and the EICs based only on the crystal structure. Finally, we benchmark our method on ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ to estimate the strength and anisotropy of the EIC.

Hall field induced resistance oscillations (HIROs) are studied in two-dimensional electron gases with resistivities dominated by scattering at identical but randomly distributed circular obstacles with hard walls. For sufficiently high number densities, these obstacles dominate the HIROs, even though they remain sparse in comparison to the intrinsic scatterers. With increasing obstacle density, we observe a monotonous increase of the HIRO period up to a factor of 2. The results are interpreted in terms of a substantial localization of the Hall field around the designed obstacles, providing an alternative explanation for the HIRO scaling factor $\gamma$ in pristine two-dimensional electron gases in terms of spatially varying Hall fields.

Interaction of femtosecond optical pulses with solids is accompanied by inhomogeneous electron heating and interband transitions. In the general case it should lead to the excitation of bulk eddy currents due to the misalignment between the gradients of free electrons’ pressure and density, similarly to the Biermann battery effect. We consider typical conditions for laser ablation of metals and show that these currents significantly heat electrons and provide convective heat transfer on subpicosecond timescales. Estimated heating depth reaches several hundred nanometers, which coincides with the ablation depth of metals at optical fluences of several $\mathrm{J}/\mathrm{c}{\mathrm{m}}^2$.

Two-dimensional (2D) van der Waals magnets present a promising platform for spintronic applications due to their unique structural and electronic properties. The ability to electrostatically control their interlayer magnetic coupling between ferromagnetic and antiferromagnetic phases is particularly advantageous for the development of energy-efficient spintronic components. While effective in bilayer $\mathrm{Cr}{\mathrm{I}}_3$, achieving this control in other 2D magnets remains a challenge. In this work, we demonstrate that bilayer $\mathrm{C}{\mathrm{r}}_2\mathrm{G}{\mathrm{e}}_2\mathrm{T}{\mathrm{e}}_6$ can achieve efficient electrostatic control through interlayer hopping modulation. We show that an external electric field can effectively manipulate the FM ↔ AFM phase transition when interlayer hopping is enhanced by pressure or sliding. We further develop a four-site interlayer hopping model, revealing that the phase transition is driven by a combined effect of on-site energy splitting and interlayer electronic hopping. Extending our findings, we confirm the model's applicability to other 2D magnets such as $\mathrm{Y}{\mathrm{I}}_2$. These findings pave the way for designing novel, electrically tunable spintronic devices, offering substantial potential for energy-efficient information processing and storage.

Hybrid superconductor-semiconductor materials are fueling research in mesoscopic physics and quantum technology. Recently demonstrated smooth $\beta$-Sn superconductor shells, due to the increased induced gap, are expanding the available parameter space to new regimes. Fabricated on quasiballistic InSb nanowires, with careful control over the hybrid interface, Sn shells yield measurable switching currents even when nanowire resistance is of order $10\mathrm{k}\mathrm{\Omega }$. In this regime Cooper pairs travel through a purely one-dimensional quantum wire for at least part of their trajectory. Here, we focus on the evolution of proximity-induced supercurrent in magnetic field parallel to the nanowire. Long decay up to fields of 1T is observed. At the same time, the decay for higher occupied subbands is notably faster in some devices but not in others. We analyze this using a tight-binding numerical model that includes the Zeeman, orbital, and spin-orbit effects. When the first subband is spin polarized, we observe a dramatic suppression of supercurrent, which is also confirmed by the model and suggests an absence of significant triplet supercurrent generation.

We study operator dynamics in many-body quantum systems, focusing on generic features of systems that are ergodic, spatially extended, and lack conserved densities. Quantum circuits of various types provide simple models for such systems. We focus on Floquet quantum circuits, comparing their behavior with what has been found previously for circuits that are random in time. Floquet circuits, which have discrete time-translation symmetry, represent an intermediate case between circuits that are random in time and lack any symmetry, and systems with a time-independent Hamiltonian and continuous time-translation invariance. By making this comparison, one of our aims is to identify signatures of time-translation symmetry in Floquet operator dynamics. To characterize behavior we examine a variety of quantities in solvable models and numerically: operator autocorrelation functions; the partial spectral form factor; the out-of-time-order correlator (OTOC); and the paths in operator space that make the dominant contributions to the ensemble-averaged autocorrelation functions. Our most striking result is that ensemble-averaged autocorrelation functions show behavior that is distinctively different in Floquet systems compared to systems in which successive time-steps are independent. Specifically, while average autocorrelation functions decay on a microscopic timescale for circuits that are random in time, in Floquet systems they have a late-time tail with a duration that grows parametrically with the size of the operator support. In the simplest models this tail is separated from the initial decay by a minimum, so that the average autocorrelation function has an intermediate-time peak. The existence of these tails provides a way to understand deviations of the spectral form factor from random matrix behavior at times shorter than the Thouless time. In contrast to this feature in autocorrelation functions, we find no new aspects to the behavior of OTOCs for Floquet models compared to random-in-time circuits. We show that this difference between averaged autocorrelation functions and OTOCs can be understood in terms of the paths in operator space that contribute to the two quantities: paths for the former retain a limited support at late times, while paths for the latter are dominated by operator spreading.

Flexomagnetism refers to the interplay of strain gradient and magnetization, but intrinsic flexomagnetic effect is usually weak due to the symmetry breaking inconsistency between ferromagnetism related time reversal and strain gradient related space reversal. Herein we demonstrate a large flexomagnetic response in monolayer CrN by applying a constant strain gradient, and thus achieve a macroscopic flexomagnetic coefficient around $250{\mu }_{\text{B}}\AA$ that is two orders of magnitude higher than the previously reported intrinsic value (in the order of $1{\mu }_{\text{B}}\AA$). The large flexomagnetic response is found to be enabled by the strain gradient manipulation of Dzyaloshinskii-Moriya interaction (DMI), and thus the associated topological magnetic textures. It is revealed that a shear-strain gradient can effectively regulate DMI strength and modulate the topological magnetic textures including Néel-type skyrmion size/shape, domain walls, and magnetic domains in monolayer CrN. Our results could inspire the exploration of flexomagnetism using the strain-gradient engineering of topological magnetic textures in monolayers instead of multilayers.

Magnetotransport measurements of $\mathrm{P}{\mathrm{r}}_4\mathrm{N}{\mathrm{i}}_3{\mathrm{O}}_{10}$ single crystals performed under externally applied pressures up to 73 GPa in diamond anvil cells with either KBr or Nujol oil as pressure media yield signatures of superconductivity with a maximum onset temperature of approximately 31 K. True zero resistance was not observed, consistent with a nonpercolating superconducting volume fraction. Magnetization measurements provided corroborating evidence of superconductivity, with a pressure-dependent diamagnetic signal occurring below the onset temperature, and an estimate from the absolute value of the susceptibility suggests a superconducting volume fraction on the order of 10%. We observe sample to sample variations in the magnitude and pressure dependence of $T_c$ as well as a dependence on the configuration of electrical contacts on a given sample. Possible causes of this behavior may be significant inhomogeneities in the pressure and/or damage to the samples induced by the pressure media as well as inhomogeneities in the crystals themselves. The results imply that our as-grown $\mathrm{P}{\mathrm{r}}_4\mathrm{N}{\mathrm{i}}_3{\mathrm{O}}_{10}$ single crystals are not bulk superconductors but that there is a minority structure present within the crystals that is indeed superconducting.

Strong coupling between light and matter generates hybrid polariton modes. We present a continuum formalism that expresses the polariton modes in terms of light and matter densities of states (DOS). We derive exact expressions for the light and matter DOS for a planar cavity containing a strongly dispersive dielectric. We show that these DOS depend exclusively on the linear response of the cavity components, i.e., the reflectance of the mirrors and the susceptibility of the dielectric. We further show that, within the strong coupling regime, the light and matter DOS are well approximated by coupled mode theory. Altogether, our continuum formalism offers a unified treatment of polaritons that connects the framework of light-matter coupling with that of linear dispersion.

Motivated by intense research on two-dimensional spin-$\frac{1}{2}$ Kitaev materials, Kitaev spin chains and ladders, though geometrically limited, have been studied for their numerical simplicity and insights into extended Kitaev models. The phase diagrams under the magnetic field were also explored for these quasi-one-dimensional models. For an isotropic Kitaev chain, it was found that a magnetic field polarizes the ground state except along the symmetric field angle, where the chain is found to remain gapless up to a critical field strength where it enters an intriguing soliton phase before reaching the polarized state at higher field strengths. Here we study an anisotropic Kitaev chain under a magnetic field using the density matrix renormalization group technique, where the ground state has a macroscopic degeneracy with a finite gap in the absence of the magnetic field. When the field is mainly aligned parallel to the strong bond, four-site and large unit-cell ordered phases arise. In a certain angle of the field, another ordered phase characterized by a uniform chirality with six-site periodicity emerges. We employ a perturbation theory to understand such field-induced ordered phases. The effective model uncovers the presence of transverse Ising and Dzyaloshinskii-Moriya interactions between unit cells, as well as further-neighbor Ising interaction induced by the magnetic field, which collectively explain the mechanisms behind these ordered states. Open questions and challenges are also discussed.

X-ray and neutron diffraction studies were performed to investigate structural and magnetic phase transitions of the Remeika phase compound ${\mathrm{Eu}}_3{\mathrm{Ir}}_4{\mathrm{Sn}}_{13}$. The crystal structure, which belongs to the cubic space group $Pm\overline{3}n$ above $T_{\mathrm{D}}=$ 59.2 K, transforms to the tetragonal space group $P{4}_2/mnm$ below $T_{\mathrm{D}}$. Below $T_{\mathrm{N}}=$ 10.2 K, the material undergoes an antiferromagnetic ordering phase transition, with the magnetic unit cell mirroring the tetragonal crystal structure. The magnetic moments along the unique crystallographic axis exhibit full saturation, consistent with the $4f^7$ electron configuration of the ${\mathrm{Eu}}^{2+}$ ion. However, even in the magnetically ordered phase, the magnetic moments linked by the nearest-neighbor bonds in the tetragonal basal plane exhibit considerable fluctuations because the magnitude of ordered magnetic moments is less than half of the $4f^7$ state. The breaking of local inversion symmetry between Eu ion connections induces antisymmetric magnetic exchange interactions. These interactions and the conventional symmetric interactions are expected to compete with each other, leading to the observed magnetic anomalies.