4Hb-${\mathrm{TaS}}_2$ has been proposed to possess unconventional superconductivity with broken time-reversal symmetry due to distinctive layered structure, featuring a heterojunction between a 2D triangular Mott insulator and a charge-density wave metal. However, since a frustrated spin state in the correlated insulating layer is susceptible to charge ordering with carrier doping, it is required to investigate the charge distribution driven by interlayer charge transfer to understand its superconductivity. Here, we use scanning-tunneling microscopy and spectroscopy (STM/S) to investigate the charge-ordered phases of $1T\text{−}{\mathrm{TaS}}_2$ layers within 4Hb-${\mathrm{TaS}}_2$, explicitly focusing on the non-half-filled regime. Our STS results show an energy gap which exhibits an out-of-phase relation with the charge density. We ascribe the competition between onsite and nonlocal Coulomb repulsion as the driving force for the charge-ordered insulating phase of a doped triangular Mott insulator. In addition, we discuss the role of the insulating layer in the enhanced superconductivity of 4Hb-${\mathrm{TaS}}_2$.

The performance of time-resolved photoelectron spectroscopy for the study of subpicosecond dynamics of laser-heated solids is often limited by space charge effects. The consequent shift and distortion of the photoelectron spectrum induced by electrons emitted by the ultrashort pump pulse is studied here using a fully coherent approach based on experimental measurements and space charge calculations. The temporal dynamics of the valence band of a copper sample is recorded before and after an 800 nm laser pump excitation at a fluence of $750{\mathrm{mJ}/\mathrm{cm}}^2$. The probe pulse is produced using a laboratory-based high-harmonics source delivering 25 fs pulses up to 100 eV photon energy. We extract the laser-heating contribution by comparing these measurements with space charge calculations based on particle-in-cell simulations of the pump and probe electron clouds mutual interaction on their way to the detector. The deduced picosecond dynamics associated to the electronic density of states shift is attributed to lattice changes with the help of hydrodynamic simulations including the two-temperature model.

Controlling the structure and properties of perovskite materials through various handles has always been an important research direction. In this present study, constrained density functional theory calculations are performed to systematically investigate the impact of illumination on the so-called $R$ and the $T$ phases of strained $\mathrm{BiFe}{\mathrm{O}}_3$ film under different epitaxial biaxial strains. We find that the phase transition strain boundary between the two phases is barely affected by illumination. However, it is discovered that light can induce a noticeable change in the two phases population, and that both the $R$ and the $T$ phases are strongly photostrictive near the phase transition boundary, with such photostriction being mainly accounted for by a converse piezoelectric model. The results of our calculations reveal the exciting prospect of using strained phases of $\mathrm{BiFe}{\mathrm{O}}_3$ for photostrictive applications. This combined with their known functional behavior could lead to devices with exotic cross functionality.

Among the $3d$ transition metal ions doped polar $\mathrm{N}{\mathrm{i}}_3\mathrm{Te}{\mathrm{O}}_6$, Mn-doped $\mathrm{N}{\mathrm{i}}_3\mathrm{Te}{\mathrm{O}}_6$ has stimulated great interest due to its high magnetic ordering temperature and complex magnetic phases, but the mechanism of magnetoelectric (ME) coupling is far from understood. Herein we report our systematic investigation of the chemical control of magnetism, metamagnetic transition, and ME properties of $\mathrm{N}{\mathrm{i}}_{3-x}\mathrm{M}{\mathrm{n}}_x\mathrm{Te}{\mathrm{O}}_6$ single crystals in high magnetic field ($H$) up to 52 T. We present a previously unreported weak ferromagnetic behavior appeared in the $ab$ plane below 9.5 K in addition to the incommensurate helical and commensurate collinear antiferromagnetic states. In the low-field region, a spin-flop-type metamagnetic transition without any hysteresis occurs at $H_{c1}$ for $H//c$, while another metamagnetic transition accompanied with a change in electric polarization is observed at $H_{c2}$ in the high-field region both for $H//c$ and $H//ab$ above 30 K, which can be attributed to the sudden rotation of magnetic moments at Ni2 sites. The ME measurements reveal that a first-order ME effect is observed in the low-$T$ and low-$H$ regions, while a second-order ME coupling term appears above 30 K in the magnetic field range of $H_{c1}<H<H_{c2}$ for $H//c$ and $H<H_{c2}$ for $H//ab$, both becoming significant with increasing temperature. Eventually, they are dominated by the second-order ME effect near the antiferromagnetic transition temperature. The present work demonstrates that $\mathrm{N}{\mathrm{i}}_{3-x}\mathrm{M}{\mathrm{n}}_x\mathrm{Te}{\mathrm{O}}_6$ is an exotic magnetoelectric material compared with $\mathrm{N}{\mathrm{i}}_3\mathrm{Te}{\mathrm{O}}_6$ and its derivatives, thereby providing insights to better understand the magnetism and ME coupling in $\mathrm{N}{\mathrm{i}}_3\mathrm{Te}{\mathrm{O}}_6$ and its derivatives.

Conserved-charge densities are very special observables in quantum many-body systems as, by construction, they encode information about the dynamics. Therefore, their evolution is expected to be of much simpler interpretation than that of generic observables and to return universal information on the state of the system at any given time. Here, we study the dynamics of the fluctuations of conserved $U\left(1\right)$ charges in systems that are prepared in charge-asymmetric initial states. We characterize the charge fluctuations in a given subsystem using the full-counting statistics of the truncated charge and the quantum entanglement between the subsystem and the rest resolved to the symmetry sectors of the charge. We show that, even though the initial states considered are homogeneous in space, the charge fluctuations generate an effective inhomogeneity due to the charge-asymmetric nature of the initial states. We use this observation to map the problem into that of charge fluctuations on inhomogeneous, charge-symmetric states and treat it using a recently developed space-time duality approach. Specializing the treatment to interacting integrable systems we combine the space-time duality approach with generalized hydrodynamics to find explicit predictions.

The concept of Hilbert space fragmentation (HSF) has recently been put forward as a routine to break quantum ergodicity. Although HSF exists widely in models with dynamical constraints, it is still challenging to tune it. Here, we propose a scheme to tune the HSF in a one-dimensional tilted lattice of interacting spinless fermions with periodically driven tunneling. For weak tunneling strength, the dynamics for a long range of time is governed by effective Hamiltonians with kinetic constraints, which appear as density-dependent tunneling. Through a Floquet time-dependent perturbation theory, we analytically derive two different resonance frequencies, at which some particular tunneling processes are resonant. At the nonresonance frequencies, the system is strongly constrained and exhibits a strong HSF. At the two different resonance frequencies, the kinetic constraints are partly released and the system exhibits another two different strong HSFs. We can tune the HSF by changing the driving frequency. We support the perturbation analysis with exact numerical simulation of the entanglement entropy, the density correlation functions, and the saturated local density profiles. Our result provides a promising way to control HSF through Floquet engineering.

We map out the ground-state phase diagram of a one-dimensional $\mathrm{SU}\left(N\right)$ Kondo-Heisenberg lattice model at half-filling and in the fully antisymmetric self-adjoint representation as a function of $\frac{1}{N}$ and Kondo coupling $J_k/t$. On the basis of auxiliary field quantum Monte Carlo (QMC) simulations with even $N$ up to 8, we show that the enlarged $\mathrm{SU}(N\ge 4$) symmetry realizes a quantum phase transition separating a valence bond solid (VBS) phase occupying a weak-coupling part of the phase diagram and the Kondo insulator (KI) state dominating in the strong $J_k/t$ limit. Along the phase boundary, we always observe critical exponents that belong to a two-dimensional classical Ising universality class. We next trace the evolution of the composite fermion and spin spectral functions across the phase boundary and conclude that VBS order triggers a bond order wave state of conduction electrons, both coexisting with Kondo screening. Upon further reducing $J_k/t$, we observe that composite quasiparticles lose their spectral weight indicating that VBS order gradually liberates localized $f$ spins from forming Kondo singlets with conduction electron spins. We contrast the QMC results with a static large-$N$ approximation, and we show that in the limit of infinite degeneracy $N\to \infty$ the order-disorder transition becomes of first order and is accompanied by a full decoupling of conduction electrons and localized $f$ spins. We complete our analysis by considering the limit of a vanishing Heisenberg coupling $J_h=0$, and we provide evidence that the enlarged $\mathrm{SU}\left(N\right)$ symmetry and low dimensionality of the Ruderman-Kittel-Kasuya-Yosida exchange interaction are not sufficient to induce VBS order in the conventional $\mathrm{SU}\left(N\right)$ Kondo chain, which hosts solely a KI phase. Finally, we quantify the role of increasing $N$ in reducing the separation of charge and spin timescales specific to the KI state, and we show that the latter is adiabatically connected to a trivial band insulator captured by the large-$N$ approximation.

Rhombohedral (ABC) stacked multilayer graphene hosts low-energy flat bands, which have proven to be an ideal platform toward achieving interaction-driven physics including superconductivity and ferromagnetism. However, of the two common multilayer graphene configurations, ABC stacked graphene is less energy favorable than the Bernal (ABA), as a result, experimental realization of large-area ABC stacked graphene is still big challenge up till now. Here we report a facile method to controllably realize a sub-micrometer-scale ABC stacked trilayer graphene (ABC-TG). By rotating graphene monolayer relative to a bilayer with a tiny angle, we observe a large-area and periodic ABC-TG region after atomic reconstruction. Our experiment indicates that the obtained ABC-TG region is rather stable under thermal annealing and pulse voltages. Using scanning tunneling microcopy (STM), we demonstrate that the flat bands of the ABC-TG region exhibit a pronounced size-dependent characteristic when the size of ABC-TG is smaller than about 100 nm, whereas, the bandwidth of the flat bands becomes a constant when the size is larger than about 100 nm, implying a minimal size for exploring emergent correlated physics in the ABC stacked graphene.

The recent synthesis of ruthenium trihalides $\mathrm{Ru}{X}_3$ ($X$ = Cl, Br, I) has enlarged the set of material candidates for Kitaev spin liquids. The realization of the Kitaev model necessitates the formation of $J=1/2$ pseudospins in the octahedral crystal field. We use Ru $L_3$-edge resonant inelastic x-ray scattering to investigate the evolution of multiplet structures in $\mathrm{Ru}{X}_3$. We identified quasielastic magnetic correlations and spin-orbit transitions to the $J=3/2$ states without discernible trigonal splitting, thereby validating the $J=1/2$ description of magnetism in the $\mathrm{Ru}{X}_3$ family. Lineshape broadening in ${\mathrm{RuI}}_3$ provides evidence for its bulk metallicity in the vicinity of a bandwidth-controlled metal-insulator transition. Our results highlight the pivotal role of halogen $p$ orbitals in controlling the electronic properties of $\mathrm{Ru}{X}_3$.

We investigate topological superconductivity in the Rashba-Hubbard model, describing heavy-atom superlattice and van der Waals materials with broken inversion. We focus in particular on fillings close to the van Hove singularities, where a large density of states enhances the superconducting transition temperature. To determine the topology of the superconducting gaps and to analyze the stability of their surface states in the presence of disorder and residual interactions, we employ an $\mathrm{fRG}+\mathrm{MFT}$ approach, which combines the unbiased functional renormalization group (fRG) with a real-space mean-field theory (MFT). Our approach uncovers a cascade of topological superconducting states, including $A_1$ and $B_1$ pairings, whose wave functions are of dominant $p$- and $d$-wave character, respectively, as well as a time-reversal breaking $A_1+i{B}_1$ pairing. While the $A_1$ and $B_1$ states have first-order topology with helical and flat-band Majorana edge states, respectively, the $A_1+i{B}_1$ pairing exhibits second-order topology with Majorana corner modes. We investigate the disorder stability of the bulk superconducting states, analyze interaction-induced instabilities of the edge states, and discuss implications for experimental systems.

Starting from the centrosymmetric ${\mathrm{MnRMnSbO}}_6$ compound, we explore the realm of magnetic polar double-double perovskite oxides characterized by significant ferroelectric polarization. Employing symmetry operations, first-principles methodologies, and Monte Carlo simulations, our investigation delves into the structural, magnetic, ferroelectric, and electronic attributes of the polar ${\mathrm{LaFeMnNiO}}_6$ and ${\mathrm{LaTiMnNiO}}_6$ compounds. Structural analysis uncovers that the paraelectric-ferroelectric phase transition is intricately linked to the Fe/Ti displacement of square-planar $\mathrm{Fe}/{\mathrm{TiO}}_4$. Notably, the magnetic ${\mathrm{LaFeMnNiO}}_6$ and ${\mathrm{LaTiMnNiO}}_6$ compounds demonstrate robust ferroelectric polarizations, measuring 20.0 and $21.8\text{µ}\mathrm{C}/{\mathrm{cm}}^2$, respectively, accompanied by minimalist forbidden energy gaps of 1.40 and 1.18 eV using the generalized gradient approximation $+U$ method. Furthermore, we pinpoint elevated magnetic transition temperatures for these compounds. Additionally, our study scrutinizes the energies associated with diverse spin configurations and identifies potential minimum decomposition pathways into stable oxides. This comprehensive analysis ensures the meticulous formation of the ${\mathrm{LaFeMnNiO}}_6$ and ${\mathrm{LaTiMnNiO}}_6$ compounds.

Recent interest in two-dimensional dichalcogenide materials is compounded by an anisotropic spin-orbit coupling (SOC) and proximity to competing orders like charge density wave (CDW), spin density wave, and superconductivity. In monolayer $2H\text{−}{\mathrm{NbSe}}_2$, the low-energy electronic structure is influenced by the presence of an Ising SOC, the formation of a 3Q CDW order $(Q=2/3\mathrm{\Gamma }M)$, and a nontrivial topology that includes the electronic environment near impurities and edges. Scanning tunneling microscopy (STM) experiments have observed a transition from a 3Q CDW order on the surface to a 1Q charge stripe order near its edges, and the presence of impurities leads to a nontrivial dependence of superconducting transition temperature on impurity concentration. First-principle calculations also predict that the material will have strong paramagnetic fluctuations and lie close to a magnetic instability. In this work, we use a realistic multiorbital model derived from density functional theory (DFT) calculations, and we implement it on a real-space Hamiltonian to study the interplay between Ising SOC, charge density wave, and a proximate magnetic order. We find that near inhomogeneities like impurities and edges, such an interplay can lead to interesting local charge and magnetic signatures that are in agreement with experimental observations such as 1Q CDW order near the material edge. We also find that due to an interplay with the underlying CDW state, the local electronic order near certain impurity sites in monolayer $2H\text{−}{\mathrm{NbSe}}_2$ can show a twofold-symmetric pattern. Finally, we propose that strong spin fluctuations can lead to the formation of local magnetic order near disorder and influence the electronic properties of this material.

We explore the critical properties of a topological transition in a two-dimensional, amorphous lattice with randomly distributed points. The model intrinsically breaks the time-reversal symmetry without an external magnetic field, akin to a Chern insulator. Here, the topological transition is induced by varying the density of lattice points or adjusting the mass parameter. Using the two-terminal conductance and multifractality of the wave function, we found that the topological transition belongs to the same universality class as the integer quantum Hall transition. Regardless of the approach to the critical point across the phase boundary, the localization length exponent remains within $\nu \approx 2.55–2.61$. The irrelevant scaling exponent for both the observables is $y\approx 0.3\left(1\right)$, comparable to the values obtained using transfer matrix analysis in the Chalker-Coddigton network. Additionally, the investigation of the entire distribution function of the inverse participation ratio at the critical point shows possible deviations from the parabolic multifractal spectrum at the anomalous quantum Hall transition.

Localized control of magnetism is one of the fundamental aspects in the development of spintronic applications. In this article, we report the observation of electrically controllable layer-dependent unique magnetization reversal in the ferromagnetic Janus van der Waals material CrSTe with robust perpendicular magnetic anisotropy. We propose an electrical shielding mechanism based on charge and spin redistribution in the system that modulates the localized spin flipping restricted to a single magnetic layer. These observations demonstrate the possibility of a purely electrically controllable, compact, low-power-consuming spintronic device consisting of a few atomic layers of a single material.

We report field-dependent high-resolution inelastic neutron scattering (INS) measurements on the honeycomb lattice magnet, ${\mathrm{CoTiO}}_3$, to study the evolution of its magnon excitations across a spin reorientation transition driven by an in-plane magnetic field. By carrying out elastic neutron scattering in a magnetic field, we show that the sample transitions from a collinear antiferromagnetic state with multiple magnetic domains at a low field to a monodomain state with a canted magnetic structure at a high field. Concurrent with this transition, we observed significant changes in both the energy and the width of the zone center magnon peak. The observed width change was argued to be consistent with an unusual zero-field state with extended domain walls. On the other hand, the magnon spectra near the $\mathbf{K}$ point of the Brillouin zone boundary were found to be largely insensitive to the changes in the ordered moment directions and the domain configuration. We argue that this observation is difficult to explain within the framework of the bond-dependent model proposed in a recent INS study [M. Elliot et al., Nat. Commun. 12, 3936 (2021)]. Our paper therefore calls for alternative explanations for the observed $\mathbf{K}$-point gap in ${\mathrm{CoTiO}}_3$.

Temperature variation of the lower critical field $H_{c1}\left(T\right)$ in the structurally disordered superconductor ${\mathrm{Y}}_5{\mathrm{Rh}}_6{\mathrm{Sn}}_{18}$ with a transition temperature $T_c\simeq 3.2$ K was investigated using micro-Hall-probe magnetometry for local magnetization measurements. Down to about $0.45T_c$, an $H_{c1}\left(T\right)$ dependence typical for a single-band $s$-wave BCS superconductor was observed. However, deep within the superconducting state, a sudden increase of $H_{c1}\left(T\right)$ was found, indicating the presence of a two-band effect. By applying the two-gap $\gamma$ model to ${\mathrm{Y}}_5{\mathrm{Rh}}_6{\mathrm{Sn}}_{18}$, we revealed a very weak interband coupling in this skutterudite-related material. We speculate that the two-band superconductivity in ${\mathrm{Y}}_5{\mathrm{Rh}}_6{\mathrm{Sn}}_{18}$ is a base for the boosted $T_c$ in slightly doped samples, which likely reflects a mechanism for enhancing superconductivity by disorder.

Interest in the superconducting proximity effect has been ignited for its crucial role in various superconducting quantum devices, together with the potential to construct topological superconductivity. In this work, monolayer Fe (Te, Se) as a high-critical temperature ($T_c$) superconductor is epitaxially grown on semiconducting $\mathrm{SrTi}{\mathrm{O}}_3$ (STO) substrates with a nominal coverage less than 1, to generate coplanar heterostructures of monolayer Fe (Te, Se) and STO. A proximity-induced full superconducting gap is detected on STO with an intriguingly extended decay length when the boundary is formed by a Fe (Te, Se) submonolayer terrace. The $T_c$, gap anisotropy, and possible causes of such proximity-induced superconductivity are discussed in detail, which provides insights into the interfacial superconductivity in the heterostructure of a low-dimensional superconductor and a semiconductor, and might pave the way for fabricating better high-$T_c$ superconductor-semiconductor devices.

When the perpendicular magnetic flux per unit cell in a crystal is equal to the quantum of the magnetic flux, ${\mathrm{\Phi }}_0=h/e$, we enter the “Hofstadter regime.” The large unit cell of moiré materials such as magic-angle twisted bilayer graphene (MATBG) allows the experimental study of this regime at feasible values of the field around 20 to 30 T. In this work, we report the numerical analysis of a tight-binding model for MATBG at one quantum of external magnetic flux, including the long-range Coulomb and on-site Hubbard interaction. We study the correlated states for dopings of $-2,0$, and 2 electrons per unit cell at the mean-field level. We find competing insulators with Chern numbers 2 and 0 at positive doping, the stability of which is determined by the dielectric screening, which opens up the possibility of observing a topological phase transition in this system.

${\mathrm{CuTeO}}_4$ has been proposed as a crystallographically distinct, yet electronic structure analog, of the superconducting cuprates. Here, we present a detailed characterization of the physical properties of ${\mathrm{CuTeO}}_4$ to address this proposal. Fitting of magnetic susceptibility data indicates unexpected quasi-one-dimensional, antiferromagnetic correlations at high temperature, with a nearest-neighbor Heisenberg exchange of $J_1=164\left(5\right)$ K. Low-temperature heat capacity measurements reveal a sizable $T$-linear contribution of $\gamma =9.58\left(8\right)$ mJ ${\text{mol}}^{-1}{\text{K}}^{-2}$, qualitatively consistent with expectations for a $S=1/2$, uniform, Heisenberg spin chain. Below $T\approx 40$ K, the susceptibility shows an upturn inconsistent with quasi-one-dimensional behavior. While heat capacity measurements show no signs of magnetic order down to low-temperature, the upturn in the magnetic susceptibility coincides with the emergence of a diffuse peak (centered at $|\vec{\mathit{Q}}|\approx 0.7$ Å) in the neutron diffraction data, indicative of persistent, short-range, antiferromagnetic order with a correlation length of $\xi =10.1\left(9\right)$ Å at $T=10$ K. The onset of nonlinearity and hysteresis in the isothermal magnetization curves suggests the presence of a small ferromagnetic component. This persistent, short-range order is understood in the context of structural modeling of the x-ray and neutron diffraction data that show the presence of a significant density of stacking faults. No evidence for substantive dopability is observed and ${\mathrm{CuTeO}}_4$ appears, qualitatively, to have a larger band gap than predicted by density functional theory. We ascribe this finding to the inductive withdrawal effect from high-valence Te and suggest that superconductivity in copper tellurates is more likely to be found in compounds with a decreased reductive withdrawal effect from Te.