Estimating many-body effects that deviate from an independent particle approach has long been a key research interest in condensed matter physics. Layered cuprates are prototypical systems, where electron-electron interactions are found to strongly affect the dynamics of single-particle excitations. It is, however, still unclear how the electron correlations influence charge excitations, such as plasmons, which have been variously treated with either weak or strong correlation models. In this work, we demonstrate the hybridized nature of collective valence charge fluctuations leading to dispersing acoustic-like plasmons in hole-doped ${\mathrm{La}}_{1.84}{\mathrm{Sr}}_{0.16}{\mathrm{CuO}}_4$ and electron-doped ${\mathrm{La}}_{1.84}{\mathrm{Ce}}_{0.16}{\mathrm{CuO}}_4$ using the two-particle probe, resonant inelastic x-ray scattering. We then describe the plasmon dispersions in both systems, within both the weak-coupling mean-field random phase approximation (RPA) and strong-coupling $t\text{−}J\text{−}V$ model in a large-$N$ scheme. The $t\text{−}J\text{−}V$ model, which includes the correlation effects implicitly, accurately describes the plasmon dispersions as resonant excitations outside the single-particle intraband continuum. In comparison, a quantitative description of the plasmon dispersion in the RPA approach is obtained only upon explicit consideration of renormalized electronic band parameters. Our comparative analysis shows that electron correlations significantly impact the low-energy plasmon excitations across the cuprate doping phase diagram, even at long wavelengths. Thus, complementary information on the evolution of electron correlations, influenced by the rich electronic phases in condensed matter systems, can be extracted through the study of two-particle charge response.

Understanding the dynamics of open quantum many-body systems is a major problem in quantum matter. Specifically, efficiently solving the spectrum of the Liouvillian superoperator governing such dynamics remains a critical open challenge. Here, we put forward a method for solving the many-body Liouvillian spectrum and dynamics based on the non-Hermitian kernel polynomial method and tensor-network techniques. We demonstrate the faithfulness of our method by computing the dynamics of the dephasing quantum compass model with a gradient magnetic field and comparing it with exact results. In particular, we show that our method allows us to characterize the quantum Zeno crossover and the reduction of relaxation rate due to Stark localization in this model. We further demonstrate the ability of our method to go beyond exact results by exploring nearest-neighbor interaction effects on the Liouvillian dynamics, elucidating the interplay between Stark localization and many-body interactions. Our method provides an efficient solution to many-body Liouvillian spectrum and dynamics, establishing a methodology to explore large open quantum many-body systems.

Hall anomaly related to deviations in Hall carrier concentrations have always been recognized as signs of charge incoherence in organic semiconductors, which lack ordered lattices. In this paper, we show that the Hall carrier concentration anomaly in doped polymers might be a result of semimetallization. Based on the observation of semimetal-like states, a dual-channel model, in which electrons and holes compensate the Hall voltages of each other, is employed to account for the anomaly. Observations of possible nonlinear Hall effect and temperature dependent Hall signs further support the origin of Hall anomaly from semimetal states.

We analyze the effects on the structural and electronic properties of vanadium dioxide (${\mathrm{VO}}_2$) due to adding an empirical interatomic potential within the density-functional $\mathrm{theory}+V$ ($\mathrm{DFT}+V$) framework. We use the $\mathrm{DFT}+V$ machinery founded on the extended Hubbard model to apply an empirical self-energy correction between nearest-neighbor vanadium atoms in both rutile and monoclinic phases, and for a set of structures interpolating between these two cases. We observe that imposing an explicit intersite interaction $V$ along the vanadium–vanadium chains enhances the characteristic bonding-antibonding splitting of the relevant bands in the monoclinic phase, thus favoring electronic dimerization and the formation of a bandgap. We then explore the effect of $V$ on the structural properties and the relative energies of the two phases, finding an insulating global energy minimum for the monoclinic phase, consistent with experimental observations. With increasing $V$, this minimum becomes deeper relative to the rutile structure, and the transition from the metallic to the insulating state becomes sharper. We also analyze the effect of applying the $+V$ correction either to all or only to selected vanadium–vanadium pairs and both in the monoclinic as well as the metallic rutile phase. Our results suggest that $\mathrm{DFT}+V$ can indeed serve as a computationally inexpensive unbiased way of modeling ${\mathrm{VO}}_2$ which is well suited for studies that, e.g., require large system sizes.

We consider optical response in multiband, multilayer two-dimensional superconductors. Within a simple model, we show that linear response to AC gating can detect collective modes of the condensate, such as Leggett and clapping modes. We show how trigonal warping of the superconducting order parameter can help facilitate detection of clapping modes. Taking rhombohedral trilayer graphene as an example, we consider several possible pairing mechanisms and show that all-electronic mechanisms may produce in-gap clapping modes. These modes, if present, should be detectable in the absorption of microwaves applied via the gate electrodes, which are necessary to enable superconductivity in this and many other settings; their detection would constitute strong evidence for unconventional pairing. Last, we show that absorption at frequencies above the superconducting gap $2\left|\mathrm{\Delta }\right|$ also contains a wealth of information about the gap structure. Our results suggest that linear spectroscopy can be a powerful tool for the characterization of unconventional two-dimensional superconductors.

Ultrafast optical excitations allow creating new metastable and hidden states in quantum materials. However, the fundamental material properties required to support new emergent order are largely unknown. Here, we show for two colossal magnetoresistive (CMR) manganites that electronic phase separation (EPS) strongly favors nonthermal behavior and exploit this to stabilize an optically induced conducting state. Our results shed light on the role of EPS in the optical control of CMR manganites and provide guidance for the design of materials that can exhibit nonequilibrium states of matter.

We propose a network-model realization of magnetic higher-order topological phases (HOTPs) in the presence of the combined space-time symmetry $C_4\mathcal{T}$—the product of a fourfold rotation and time-reversal symmetry. We show that the system possesses two types of HOTPs. The first type, analogous to Floquet topology, generates a total of eight corner modes at 0 or $\pi$ eigenphase, while the second type, hidden behind a weak topological phase, yields a unique phase with eight corner modes at $\pm \pi /2$ eigenphase (after gapping out the counterpropagating edge states), arising from the product of particle-hole and phase-rotation symmetry. By using a bulk ${\mathbb{Z}}_4$ topological index $\left(Q\right)$, we found both HOTPs have $Q=2$, whereas $Q=0$ for the trivial and the conventional weak topological phase. Together with a ${\mathbb{Z}}_2$ topological index associated with the reflection matrix, we are able to fully distinguish all phases. Our work motivates further studies on magnetic topological phases and symmetry-protected $2\pi /n$ boundary modes, as well as suggesting that such phases may find their experimental realization in coupled-ring-resonator networks.

The magnetic skyrmion is described by one control parameter and one length scale. We study the two extreme limits of the control parameter, infinitely large and vanishing, and find that the magnetic skyrmion becomes a “restricted” magnetic skyrmion and an $\mathrm{O}\left(3\right)$ sigma model lump, respectively. Depending on the potential under consideration, the restricted limit manifests differently. In the case of the Zeeman term, the restricted magnetic skyrmion becomes a “supercompacton” that develops a discontinuity, whereas for the Zeeman term to the power $\frac{3}{2}$ it becomes a normal compacton. In both the lump and the restricted limit the solution is given in exact explicit form. We observe that the case of the Zeeman term squared, which can also be understood as a special combination of the Zeeman term and the easy-plane potential (realizable in the laboratory), the analytically exact solution for all values of the coupling, including the Bogomol'nyi-Prasad-Sommerfield case, is also of the lump type. Finally, we notice that certain materials (e.g., ${\mathrm{Fe}}_{1\text{−}x}{\mathrm{Co}}_x\mathrm{Si}$ or ${\mathrm{Mn}}_{1\text{−}x}{\mathrm{Fe}}_x\mathrm{Ge}$) have a rather large control parameter $\epsilon$ of order 100, making the restricted limit a suitable rough approximation.

We introduce a diagrammatic multi-scale approach to the Hubbard model based on the interaction-irreducible (multi-boson) vertex of a small cluster embedded in a self-consistent medium. The vertex captures short-range correlations up to the length scale of the cluster, while long-range correlations are recovered from a set of diagrammatic equations for the Hedin three-leg vertex. By virtue of the crossing symmetry, the Fierz decoupling ambiguity of the Hubbard interaction is resolved exactly. Our benchmarks for the half-filled Hubbard model on the square lattice are in very good agreement with numerically exact diagrammatic Monte Carlo simulations.

We determine the Dzyaloshinskii-Moriya interaction within and between two magnetic cobalt layers separated by a nonmagnetic spacer through ab initio calculations. We investigate different materials for the nonmagnetic layer, focusing on the experimentally realized Co/Ag/Co system. We laterally shift the atoms in the nonmagnetic layer to achieve the symmetry breaking required for the interlayer Dzyaloshinskii-Moriya interaction. We compare the resulting interactions with the Levy-Fert model and observe a good overall agreement between the model and the ab initio calculations for the dependence on the atomic positions. Additionally, we derive a formula for the strength of the interlayer isotropic exchange interaction depending on the position of the atoms in the nonmagnetic layer and compare it to the first-principles results. We investigate the limitations of the Levy-Fert model by turning off the spin-orbit coupling separately on the nonmagnetic and magnetic atoms and by studying the effect of band filling. Our work advances the understanding of the microscopic mechanisms of the interlayer Dzyaloshinskii-Moriya interaction and gives insight into possible new material combinations with strong interlayer Dzyaloshinskii-Moriya interaction.

We show that hematite, $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$, below its Morin transition, has a ferroic ordering of rank-5 magnetic triakontadipoles on the Fe ions. In the absence of spin-orbit coupling, these are the lowest-order ferroically aligned magnetic multipoles, and they give rise to the $g$-wave nonrelativistic spin splitting in hematite. We find that the ferroically ordered magnetic triakontadipoles result from the simultaneous antiferroic ordering of the charge hexadecapoles and the magnetic dipoles, providing a route to manipulating the magnitude and the sign of the magnetic triakontadipoles as well as the spin splitting. Furthermore, we find that both the ferroic ordering of the magnetic triakontadipoles and many of the spin-split features persist in the weak ferromagnetic phase above the Morin transition temperature.

We calculated the structural, electronic, and magnetic properties of FeSe within density-functional theory at the generalized gradient approximation level. First, we studied how the bandwidth of the $d$-bands at the Fermi energy is renormalized by adding simple corrections: Hubbard $U$, Hund's $J$, and by introducing long-range magnetic orders. We found that introducing either a striped or a staggered dimer antiferromagnetic order brings the bandwidths—which are starkly overestimated at the generalized gradient approximation level—closer to those experimentally observed. Second, for the ferromagnetic, the striped, checkerboard, and staggered dimer antiferromagnetic order, we investigate the change in magnetic formation energy with local magnetic moment of Fe at a pressure up to 6 GPa. The bilinear and biquadratic exchange energies are derived from the Heisenberg model and noncollinear first-principles calculations, respectively. We found a nontrivial behavior of the spin-exchange parameters on the magnetization, and we put forward a field-theory model that rationalizes these results in terms of two-dimensional spin and orbital fluctuations. The character of these fluctuations can be either that of a standard density wave or a topological vortex. Topological vortices can result in mesoscopic magnetization structures.

A Gaussian quantum theory of bosonic modes has been widely used to describe quantum optical systems, including coherent Ising machines (CIMs) that consist of ${\chi }^{\left(2\right)}$ degenerate optical parametric oscillators (DOPOs) as nonlinear elements. However, Gaussian models have been thought to be invalid in the extremely strong-gain-saturation limit. Here, we develop an extended Gaussian model including two third-order fluctuation products, $\langle \delta {\widehat{X}}^3\rangle$ and $\langle \delta \widehat{X}\delta {\widehat{P}}^2\rangle$, which we call self-skewness and cross-skewness, respectively. This new model which we call the skew-Gaussian model more precisely replicates the success probability predicted by the quantum master equation (QME), relative to Gaussian models. We also discuss the impact of skew variables on the performance of CIMs.

Experimental indications have been reported suggesting that laser pulses shining on materials with relativistic dispersion can produce currents that survive long after the illumination has died out. Such residual currents, i.e., remnant currents, have applications in petahertz logical gates. The remnant currents' strength strongly depends on the pulse shape. We develop an analytical formula that allows one to optimize the pulse shape for remnant current production; we predict remnant currents exceeding the values observed so far by up to five orders of magnitude. This can be achieved by using single-cycle pulses instead of the previously employed multicycle pulses. In fact, remnant currents can be almost as strong as the peak current under irradiation.

In the search of quantum spin liquid (QSL), spin-1/2 triangular-lattice Heisenberg antiferromagnets have always been viewed as fertile soils. Despite the true magnetically ordered ground state, anisotropy has been considered to play a significant role in stabilizing a QSL state. However, the nature and ground state of the most anisotropic case, the triangular-lattice Ising antiferromagnet (TLIAF), remain elusive and controversial. Here, we report specific-heat and thermal-conductivity measurements on a newly discovered Ising-type QSL candidate ${\mathrm{PrMgAl}}_{11}{\mathrm{O}}_{19}$. At zero field, the magnetic specific heat shows a quadratic temperature dependence. On the contrary, no direct positive magnetic contribution to thermal conductivity is detected, ruling out the presence of mobile gapless fermionic excitations. Further analysis of phonon thermal conductivity reveals that the phonons are strongly scattered by thermally activated magnetic excitations out of a gap, which exhibits a linear dependence with magnetic field. These results demonstrate that the spin-1/2 TLIAF ${\mathrm{PrMgAl}}_{11}{\mathrm{O}}_{19}$ has a gapped $Z_2$ QSL ground state.

We study the bulk-boundary correspondences for zigzag ribbons (ZRs) of massless Dirac fermion in the two-dimensional $\alpha \text{−}{T}_3$ lattice. By tuning the hopping parameter $\alpha \in [0,1]$, the $\alpha \text{−}{T}_3$ lattice interpolates between pseudospin $S=1/2$ (graphene) and $S=1$ ($T_3$ or dice lattice), for $\alpha =0$ and 1, respectively, which is followed by a continuous change of the Berry phase from $\pi$ to 0. The range of existence for edge states in the momentum space is determined by solving tight-binding equations at the boundaries of the ZRs. We find that the transitions of in-gap bands from bulk to edge states in the momentum space do not only occur at the positions of the Dirac cones but also at additional points depending on $\alpha \in (0,1)$. The $\alpha \text{−}{T}_3$ ZRs are mapped onto stub Su-Schrieffer-Heeger chains by performing unitary transformations of the bulk Hamiltonian. The nontrivial topology of the bulk bands is revealed by the Majorana representation of the eigenstates, where the topological invariant is manifested by winding numbers on the complex plane and the Bloch sphere.

We investigate the role of electric toroidal dipoles in the prototypical ferroaxial materials ${\mathrm{NiTiO}}_3$ and ${\mathrm{K}}_2\mathrm{Zr}{\left({\mathrm{PO}}_4\right)}_2$, which undergo ferroaxial structural phase transitions of order-disorder and displacive type, respectively. Using first-principles electronic structure theory, we compute the evolution across the ferroaxial transitions of the local electric toroidal dipole moments, defined in terms of both the vortices formed by local dipoles as well as the cross product of orbital and spin angular momenta. Our calculations confirm that the electric toroidal dipole acts as the order parameter for these ferroaxial transitions and highlight the importance of spin-orbit coupling in generating a nonzero atomic-site electric toroidal dipole moment. We find that, while the ferroaxial phases of ${\mathrm{NiTiO}}_3$ and ${\mathrm{K}}_2\mathrm{Zr}{\left({\mathrm{PO}}_4\right)}_2$ preserve global inversion symmetry, they contain inversion-symmetry-broken subunits that generate vortices of local electric dipole moments. In addition to causing the net electric toroidal dipole moment, these vortices induce a hidden spin polarization in the band structure.

In this paper, we present a promising method for modulating the frequency of magnetic droplets using strain induced by an adjacent piezoelectric layer. This strain results in significant changes in droplet frequency ($\sim 6$ GHz) and variations in diameter or mode, while maintaining a fixed current density of $1.4\times {10}^{12}\mathrm{A}/{\mathrm{m}}^2$ under both high and low fields. By applying strain pulses, we successfully modulate the magnetic droplet frequency, paving the way for potential implementation of digital binary frequency shift-keying modulation technique with magnetic droplets. Moreover, the effects of Oersted field and the Zhang-Li torque induced by lateral current have also been discussed, showing a minimal impact on the oscillation frequencies, especially at high fields.