We theoretically analyze the phase diagram of a quantum gas of bosons that interact via repulsive dipolar interactions. The bosons are tightly confined by an optical lattice in a quasi-one-dimensional geometry. In the single-band approximation, their dynamics is described by an extended Bose-Hubbard model where the relevant contributions of the dipolar interactions consist of density-density repulsion and correlated tunneling terms. We evaluate the phase diagram for unit density using numerical techniques based on the density-matrix renormalization group algorithm. Our results predict that correlated tunneling can significantly modify the parameter range of the topological insulator phase. At vanishing values of the onsite interactions, moreover, correlated tunneling promotes the onset of a phase with a large number of low-energy metastable configurations.

We study the weak-coupling limit of the $t-t^{\prime }-U$ Hubbard model on a two-dimensional square lattice using a direct perturbative approach. Aided by symbolic computational tools, we compute the longitudinal density-density correlation functions in the ${\chi }_{\uparrow \uparrow }$ and ${\chi }_{\uparrow \downarrow }$ basis from which we can obtain the dynamical spin and charge susceptibilities at arbitrary doping and temperature. We find that for nonzero $t^{\prime }$, the zero-frequency commensurate $\mathbf{q}=(\pi ,\pi )$ spin and charge excitations are each strongest at different densities and we observe a clear behavioral change that appears tied to the van Hove singularity of the noninteracting dispersion upon which the perturbative expansion is built. We find a strongly reduced compressibility in the vicinity of the van Hove singularity as well as a behavioral change in the double occupancy. For finite $t^{\prime }$, the observed van Hove singularity occurs away from half filling, leading us to conclude that this reduction in compressibility is distinct from the Mott insulating physics that one expects in the strong-coupling regime. We compute the full dynamical spin and charge excitations and observe distinct structure for electron- and hole-doped scenarios, in agreement with experiments on cuprate materials. Finally, we observe a peculiar splitting in spin and charge excitations in the vicinity of the van Hove singularity, the origin of which is traced to a splitting near the bottom of the band.

We report on the stability and magnetic state of ion implanted ${}^8\mathrm{Li}$ in single crystals of the semiconductor ZnO using $\beta$-detected nuclear magnetic resonance. At ultradilute concentrations, the spectra reveal distinct Li sites from 7.6 to 400 K. Ionized shallow donor interstitial Li is stable across the entire temperature range, confirming its ability to self-compensate the acceptor character of its (Zn) substitutional counterpart. Above 300 K, spin-lattice relaxation indicates the onset of correlated local motion of interacting defects, and the spectra show a site change transition from disordered configurations to substitutional. Like the interstitial, the substitutional shows no resolved hyperfine splitting, indicating it is also fully ionized above 210 K. The electric field gradient at the interstitial ${}^8\mathrm{Li}$ exhibits substantial temperature dependence with a power law typical of noncubic metals.

Recent studies have shown that there are two types of topological quadrupolar semimetals. One is the quadrupolar bulk semimetal, which is a conventional semimetal with gapless nodes in the bulk spectrum. The other type is named the quadrupolar surface semimetal, possessing a gapped bulk but gapless nodes on the surface spectrum. There have been many experiments on the implementation of quadrupolar bulk semimetals. Here we report on the experimental realization of the quadrupolar surface semimetal in the circuit system. To highlight the properties of the quadrupolar surface semimetal, we also prepare a quadrupolar bulk semimetal in the circuit as a contrast. It has been demonstrated that the quadrupolar surface semimetal has a bulk band gap, but two gapless nodes appear on the surfaces. Also, the electrons not only concentrate on the hinges but also on the corresponding surfaces. Our studies provide novel ways to control electrical signals and may have potential applications in the field of intergraded circuit design.

We explore the possibility of the existence of plasmonically generated electronic Floquet bands at metal surfaces by studying the gauge transformed electron-surface plasmon interaction in the prepumped plasmonic coherent state environment. These bands may promote non-Einsteinian electron emission from metal surfaces exposed to primary interactions with strong electromagnetic fields. Resonant behavior and scaling of emission yield with the parent electronic structure and plasmonic state parameters are estimated for Ag(111) surface. The obtained relative yield intensities from non-Einsteinian emission channels in photoelectron spectra offer the means to calibrate the mediating plasmonic fields and the therefrom ensuing surface Floquet bands.

The $A$-site spinel ${\mathrm{NiRh}}_2{\mathrm{O}}_4$ is the only known realization of a spin-1 diamond lattice magnet and is predicted to host unconventional magnetic phenomena driven by frustrated nearest and next-nearest neighbor exchange as well as orbital degeneracy. Previous works found no sign of magnetic order but found a gapped dispersive magnetic excitation indicating a possible valence bond magnetic ground state. However, the presence of many competing low energy degrees of freedom and limited empirical microscopic constraints complicates further analysis. Here we carry out resonant inelastic x-ray scattering (RIXS), x-ray absorption spectroscopy (XAS), and inelastic neutron scattering (INS) to characterize the local electronic structure and lattice dynamics of ${\mathrm{NiRh}}_2{\mathrm{O}}_4$. The RIXS data can be partly described by a single-ion model for tetrahedrally coordinated ${\mathrm{Ni}}^{2+}$ and indicates a tetragonal distortion $\mathrm{\Delta }{t}_2=70$ meV that splits the $t_2$ orbitals into a high energy orbital singlet and lower energy orbital doublet. We identify features of the RIXS spectra that are consistent with a Rh-Ni two-site excitation indicating strong metal-metal hybridization mediated by oxygen in ${\mathrm{NiRh}}_2{\mathrm{O}}_4$. We also identify signatures of electron-phonon coupling through the appearance of phonon sidebands that dress crystal field excitations. These results establish the key energy scales relevant to the magnetism in ${\mathrm{NiRh}}_2{\mathrm{O}}_4$ and further demonstrate that covalency and lattice dynamics play essential roles in controlling the magnetic ground states of $A$-site spinels.

The $\text{LDA}+U$ method is widely used to study the properties of realistic solids with strong electron correlations. One of its main shortcomings is that it does not provide direct access to the temperature dependence of material properties such as the magnetization, the magnetic anisotropy energy, the Dzyaloshinskii-Moriya interaction, the anomalous Hall conductivity, and the spin-orbit torque. While the method of spectral moments allows us in principle to compute these quantities directly at finite temperatures, the standard two-pole approximation can be applied only to Hamiltonians that are effectively of single-band type. We do a first step to explore if the method of spectral moments may replace the $\text{LDA}+U$ method in first-principles calculations of correlated solids with many bands in cases where the direct assessment of the temperature dependence of equilibrium and response functions is desired: The spectral moments of many-band Hamiltonians of correlated electrons do not commute and therefore they do not possess a system of common eigenvectors. We show that nevertheless the spectral function may be constructed from the spectral moments by solving a system of coupled nonlinear equations. Additionally, we show how to compute the anomalous Hall conductivity of correlated electrons from this spectral function. We demonstrate the method for the Hubbard-Rashba model, where the standard two-pole approximation cannot be applied because spin-orbit interaction (SOI) couples the spin-up and the -down bands. In the quest for new quantum states that arise from the combination of SOI and correlation effects, the Hartree-Fock approximation is frequently used to obtain a first approximation for the phase diagram. We propose that using the many-band generalization of the self-consistent moment method instead of Hartree-Fock in such exploratory model calculations may improve the accuracy significantly, while keeping the computational burden low.

Using the three-orbital Hubbard model, we investigate the low-energy excitation spectra in the antiferromagnetic phase of ${\mathrm{Ca}}_2{\mathrm{RuO}}_4$. We calculate the dynamical susceptibilities in the low-energy region by the random phase approximation and find that the anisotropic dispersion of the transverse mode is in good agreement with the spectra recently reported by inelastic neutron scattering experiments. By the fast-collision approximation, we simulate the resonant inelastic x-ray scattering (RIXS) spectra of the Ru $L_3$ edge from the dynamical susceptibilities. We show that the dispersion of the transverse mode is clearly observed in the calculated RIXS spectra and that the polarization dependence of the incident x rays enables one to distinguish between the excitations of the in-plane transverse mode and out-of-plane transverse mode.

${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$ is a van der Waals (vdW)-coupled unconventional ferromagnetic metal with a high Curie temperature ($T_{\mathrm{C}}$) exceeding 300 K. The formation of an anomalous ground state significantly below $T_{\mathrm{C}}$ has received considerable attention, resulting in increased interest in understanding the spin-polarized electronic state evolution near the Fermi energy ($E_{\mathrm{F}}$) as a function of temperature. Despite recent extensive studies, a microscopic understanding of the spin-polarized electronic structure around $E_{\mathrm{F}}$ has not yet been established owing to the intrinsic complexity of both the crystal and band structures. In this study, we investigate the temperature dependence of element-specific soft x-ray magnetic circular dichroism (XMCD). A systematic temperature evolution in the XMCD signal from both magnetic Fe and its ligand Te is clearly observed. More importantly, the enhancement in the hybridization between the Fe $3d$ and Te $5p$ states at low temperature in the zero-magnetic field limit is revealed. We discuss the implications of our observation in line with possible emergence of an exotic magnetic ground state in ${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$.

Theoretical study is performed of a single-mode polariton system with linear coupling of spin components. When combined with an ordinary two-particle interaction, the spin coupling involves a spontaneous symmetry breaking accompanied by a switch from linear to circular polarization under resonant driving. The asymmetric steady states can also lose stability, giving way to oscillatory and chaotic dynamics. Here, we explore a continuous transformation between the multistable regime, where the system is steady and locked in phase to the pump but has a broken spin symmetry, and full-span oscillations of the circular-polarization degree, owing to which the symmetry is effectively reestablished. Such oscillations are analogous to the intrinsic Josephson effect and prove to be robust against arbitrarily strong perturbations. Transitional phenomena include the Hopf bifurcation, spin bistability of limit cycles, and continuous transitions to and from dynamical chaos through series of period doubling and halving events.

Donors in silicon can now be positioned with an accuracy of about one lattice constant, making it possible to form donor arrays for quantum computation or quantum simulation applications. However, the multivalley character of the silicon conduction band combines with central cell corrections to the donor states to convert small atomic scale imperfections in donor placement into strong interdonor hybridization disorder. We present a simple model that is able to account for central cell corrections accurately, and use it to assess the impact of donor positional disorder on donor array properties in both itinerant and localized limits. Our results show that donor arrays in silicon simulate strongly disordered one-dimensional electrons.

The interaction between an exciton and acoustic phonons via the deformation potential in PbS nanocrystals is calculated in the $\mathbf{k}·\mathbf{p}$ model. It is shown that the anisotropy of the deformation potential leads to nonzero interaction of an exciton with spheroidal phonons with the total angular momentum $j=2$. The size dependence of the Huang-Rhys factors for the fundamental breathing mode and its overtones as well as for spheroidal vibrations with the total angular momentum $j=2$ is evaluated.

The photoluminescence (PL) properties of metallic single-walled carbon nanotubes were investigated. Steady-state measurements showed interband excitonic PL in the first hyperbolic dispersion region. The decay kinetics of this interband excitonic PL was observed by femtosecond time-resolved measurements, which also showed the occurrence of intraband PL in the linear dispersion region. The decay time constant of interband excitonic PL is approximately 40 fs, while that of intraband PL is slower at the lower photon energy. This study demonstrates the role of interband and intraband transitions in the PL of a one-dimensional metal.

In easy-plane ferromagnets, we show that the interplay between a domain wall and a spin wave packet can be formulated as the collision of two massive particles with a gravitylike attraction. In the presence of magnetic dissipation, the domain wall mimics a particle subject to viscous friction, while the spin wave packet resembles a particle of variable mass. Due to the attractive nature of the interaction, the domain wall acquires a backward displacement as a spin wave packet penetrating the domain wall, even though there is no change in momentum of the wave packet before and after penetration.

We have studied the electronic properties of ScS, a transition-metal monochalcogenide with a rocksalt crystal structure, using magnetization, specific heat, transport, and muon spin rotation/relaxation ($\mu \mathrm{SR}$) measurements. All measurements confirm the bulk superconductivity in ScS with a transition temperature of $T_C=5.1\left(5\right)$ K. Specific heat together with transverse-field $\mu \mathrm{SR}$ measurements indicate a full gap, while our zero-field $\mu \mathrm{SR}$ study reveals the presence of spontaneous static or quasistatic magnetic fields emerging when entering the superconducting state. We discuss various possible microscopic origins of the observed time-reversal symmetry breaking. As none of them can be readily reconciled with a conventional pairing mechanism, this introduces ScS as a candidate material for unconventional superconductivity.

We report a metal-insulator transition (MIT) in the half-filled multiorbital antiferromagnet (AFM) ${\mathrm{BaMn}}_2{\mathrm{Bi}}_2$ that is tunable by a magnetic field perpendicular to the AFM sublattices. Instead of an Anderson-Mott mechanism usually expected in strongly correlated systems, we find by scaling analyses that the MIT is driven by an Anderson localization. Electrical and thermoelectrical transport measurements in combination with electronic band calculations reveal a strong orbital-dependent correlation effect, where both weakly and strongly correlated $3d$-derived bands coexist with decoupled charge excitations. Weakly correlated holelike carriers in the $d_{xy}$-derived band dominate the transport properties and exhibit the Anderson localization, whereas other $3d$ bands show clear Mott-like behaviors with their spins ordered into AFM sublattices. The tuning role played by the perpendicular magnetic field supports a strong spin-spin coupling between itinerant holelike carriers and the AFM fluctuations, which is in sharp contrast to their weak charge coupling.

Unraveling the liquid structure of multicomponent molten salts is challenging due to the difficulty in conducting and interpreting high-temperature diffraction experiments. Motivated by this challenge, we developed composition-transferable Gaussian approximation potential (GAP) for molten LiCl-KCl. A DFT-SCAN accurate GAP is active-learned from only $\sim$1100 training configurations drawn from 10 unique mixture compositions enriched with metadynamics. The GAP-computed structures show strong agreement across high-energy x-ray diffraction experiments, including for a eutectic not explicitly included in model training, thereby opening the possibility of composition discovery.

Recent reports have shown that thulium iron garnet (TmIG) based bilayers are promising material platforms for realizing small, room-temperature skyrmions. For potential applications, it is imperative to accurately evaluate electrical readout signals of skyrmions. In this context, the topological Hall effect has been considered as a characteristic signature of skyrmion formation. Unlike previous studies that have modeled the anomalous Hall effect in ultrathin TmIG/Pt bilayers, we isolate its contribution to the electrical readout signal by directly measuring the magnetic hysteresis loops using a sensitive Sagnac magneto-optical Kerr effect technique. Our combined optical and electrical measurements reveal that the spin Hall topological Hall resistivity is considerably larger than previously estimated values. Our finding further indicates that skyrmions can exist at room-temperature and near-zero applied magnetic fields.

We theoretically examine behavior of superconductivity at parallel interfaces separating the domains of another dominant collective excitation, such as charge density waves or spin density waves. Due to their competitive coupling in a two-component Ginzburg-Landau model, suppression of the dominant order parameter at the interfacial planes allows for nucleation of the (hidden) superconducting order parameter at those planes. In such a case, we demonstrate how the number of the parallel interfacial planes and the distance between them are linked to the number and the size of the emerging superconducting gaps in the system, as well as the versatility and temperature evolution of the possible superconducting phases. These findings bear relevance to a broad selection of known layered superconducting materials, as well as to further design of artificial (e.g., oxide) superlattices, where the interplay between competing order parameters paves the way towards otherwise unattainable superconducting states, some with enhanced superconducting critical temperature.