We report magnetic susceptibility, isothermal magnetization, and specific-heat measurements on the rare-earth hexaaluminate ${\mathrm{SmMgAl}}_{11}{\mathrm{O}}_{19}$, where ${\mathrm{Sm}}^{3+}$ realizes a strongly quenched Kramers doublet on a triangular lattice with an exceptionally weak net exchange scale. Curie-Weiss analysis yields strongly reduced ground-doublet $g$ factors, $g_{ab}\simeq 0.65$ and $g_c\simeq 0.70$, indicating that the low-temperature response is governed primarily by single-ion physics, with crystal-field splitting and $J$-multiplet mixing renormalizing the ${\mathrm{Sm}}^{3+}$ moment rather than collective exchange. For $H\parallel c$, the specific heat shows no $\lambda$-type anomaly down to 0.35 K, but evolves in field into a two-level Schottky peak whose gap increases linearly with field. The Schottky analysis yields $g_c\simeq 0.62$ and recovers nearly all of $Rln2$ at high fields, supporting an effective $S_{\mathrm{eff}}=\frac{1}{2}$ Kramers doublet description for $T\lesssim 10\mathrm{K}$. Overall, the data place ${\mathrm{SmMgAl}}_{11}{\mathrm{O}}_{19}$ in an extreme weak-exchange, single-ion–dominated regime, with low-temperature deviations from ideal two-level behavior that may reflect a combination of geometric frustration, multiplet mixing, and structural disorder, while no long-range order is observed within our experimental window.

The study of quasiparticle dynamics is central to understanding nonequilibrium phenomena in quantum many-body systems. Direct simulation of such dynamics on quantum hardware has been limited by circuit depth and noise constraints. In this work, we use a recently developed constant-depth circuit algorithm to examine the real-time evolution of site-resolved magnetization in a transverse-field Ising chain on noisy intermediate-scale quantum devices. By representing each spin as a pair of Majorana fermions, we identify two distinct dynamical regimes governed by the relative strength of spin interaction. Furthermore, we show how local impurities can serve as probes of Majorana modes, acting as dynamical barriers in the weak coupling regime. These results demonstrate that constant-depth quantum circuits provide a viable route for studying quasiparticle propagation and for probing Majorana signatures on currently available quantum processors.

We present a plane-wave (PW) implementation of the auxiliary-field quantum Monte Carlo (AFQMC) method within the projector augmented-wave (PAW) formalism in the Vienna ab initio Simulation Package (VASP). By employing an exact inversion of the PAW overlap operator, our approach maintains cubic scaling while naturally incorporating all excitations defined by the PW cutoff. We benchmark this framework by calculating the equilibrium lattice constants and bulk moduli of C, BN, BP, and Si. Our analysis demonstrates that AFQMC systematically corrects the lack of long-range screening in MP2 and the missing higher-order exchange in RPA. We identify RPA as the optimal reference method because of the rapid convergence of the remaining short-range correlations with respect to supercell size. The resulting lattice constants exhibit a mean absolute relative error of $0.14\%$ relative to experiment, establishing the method as a rigorous benchmark tool for structural properties of prototypical semiconductors and insulators.

Hund's metallicity in $3d$ transition metal oxides constitutes a rare class of compounds, since they have been long understood considering the dominance of Hubbard $U$. ${\mathrm{LiV}}_2{\mathrm{O}}_4\text{and} {\mathrm{Sr}}_2{\mathrm{CoO}}_4$ belong to this rare class of metals; among them, ${\mathrm{LiV}}_2{\mathrm{O}}_4$ has been the subject of extensive investigations for its unconventional heavy-fermion behavior, while studies on ${\mathrm{Sr}}_2{\mathrm{CoO}}_4$ remain limited despite its anomalous ferromagnetic ground state. In this study, we report an unusual spin-orbital selective localization in ${\mathrm{Sr}}_2{\mathrm{CoO}}_4$ consistent with a Kondo-like resonance at $\sim 70\mathrm{K}$ in the spin-$up$ channel of orbitals of $t_{2g}$ symmetry using a combination of Density functional theory and Dynamical mean-field theory calculations. Correspondingly, an appreciable reduction in the magnetization below $T=100\mathrm{K}$ is further suggestive of a partial Kondo-like screening of local moments active at low temperatures, providing a plausible explanation for its effective spin magnetization state and upturn in its resistivity observed in experimental reports. We note a significant effect of Hund's induced spin-orbital selective incoherence in dictating the temperature evolution of its macroscopic observables e.g., spin-spin correlation function and effective local moment. Our results reveal a potentially distinct/new form of spin-dependent selectivity induced via Hund's coupling in addition to the conventional orbital-selectivity in the Hund's metals, as a plausible key mechanism in stabilizing their long-range magnetic order.

Quasiparticle interference (QPI) is a powerful tool to characterize the symmetry of the superconducting order parameter in unconventional superconductors, by mapping the spatial dependence of elastic tunneling of electrons between the tip of a scanning tunneling microscope and a sample. Here, we consider the influence of inelastic tunneling on quasiparticle interference, exemplarily for the iron-based superconductor LiFeAs. We clearly observe replica features in both experimental QPI maps and the dispersion extracted from QPI, which from comparison with theoretical model calculations can be attributed to inelastic tunneling. Analysis of the QPI dispersion shows that the inelastic mode that gives rise to these replica features exhibits a resonance between 8 and 10 meV. Comparison of the energy scale of the resonance energy estimated from QPI with inelastic neutron scattering indicates that the replica features arise from interaction with spin fluctuations.

Harnessing Rashba spin-orbit interaction and related spintronic functionalities has traditionally relied on metallic surfaces or interfaces containing elemental heavy metals. Here, using first-principles calculations and $\mathrm{Cu}\left(001\right)\text{/}{\mathrm{WO}}_3\left(001\right)$ as a model heterostructure, we show that interfacing a light metal, Cu, with a band insulator, ${\mathrm{WO}}_3$, yields an interface state, which exhibits a robust Rashba spin splitting, arising from the interplay between linear and cubic Rashba effects. The spin splitting is driven by the strong spin-orbit coupling of W atoms and enabled by W-Cu orbital hybridization at the interface. The cubic Rashba contribution asymptotically grows with Cu thickness and can be explained in terms of cross-coupling between the vacuum/Cu and $\text{Cu/}{\mathrm{WO}}_3$ interfaces. This interfacial cross-coupling, however, diminishes at larger Cu thicknesses, allowing us to extract the intrinsic cubic Rashba parameter, which amounts to a giant value of $\approx$−1.93 $\mathrm{eV}{\AA }^3$. In contrast, the linear Rashba parameter is only weakly affected by this cross-coupling and varies from $\approx +0.3$ to $+0.49 \mathrm{eV}\AA$. We further show that sizable linear and cubic Rashba effects persist across several interface geometries and Cu surface orientations including (110) and (111). Our work identifies the $\text{Cu/}{\mathrm{WO}}_3$ interface as an interesting light metal/heavy-element-based oxide platform for exploring the rich spectrum of Rashba physics, including linear and nonlinear spin-orbit phenomena.

Weyl exceptional lines typically occur in three-dimensional (3D) topological semimetals; however, they also emerge in the parameter space of one-dimensional (1D) systems. In this work, we study the impact of dissipation on the nodal ring in a 3D topological semimetal. We find that the energy spectrum becomes fully complex in the presence of dissipation, and the original nodal ring is split into two exceptional rings. We introduce a vortex field in the momentum space, generated from the spectrum, to characterize the topology of the exceptional rings. This provides a clear physical picture of the topological structure. The two exceptional rings act as two vortex filaments of a free vortex flow with opposite circulations. In this context, the 3D Hermitian topological semimetal is the boundary separating two quantum phases identified by two configurations of exceptional rings. We also propose a 1D model that exhibits a similar topological feature in the parameter space. It provides a simple way to measure the topological invariant in a low-dimensional system. Numerical simulations indicate that the topological invariant is robust under the random perturbations of the system parameters.

We introduce a family of many-body systems of distinguishable continuous-variable particles in which interparticle interactions are set by the adjacency matrix of a graph. The ground-state wave function of such systems is of a generalized Jastrow form involving the product of pair-correlation functions over the edge set of the graph. These systems describe quantum fluids when the graph is complete, and the pair function has a well-defined permutation symmetry. In general, they provide the continuous-variable generalization of spin systems on graphs, with broken permutation symmetry. The corresponding parent Hamiltonian is shown to include (a) two-body interactions determined by the graph adjacency matrix and (b) three-body interactions over all possible 2-paths on the graph. Employing elements of graph theory, we chart the landscape of models, recovering known instances in the literature and providing numerous new examples of ground-state solvable models for which the system Hamiltonian, ground-state wave function, and corresponding energy eigenvalue are specified.

Nodal-line semimetals (NLSs) can display unconventional quasiparticle dynamics and charge transport properties due to their extended band degeneracy and the peculiar geometry of their Fermi surface. We consider electron-acoustic phonon scattering as the dominant relaxation mechanism and compute the quasiparticle decay rate and dc conductivity by solving the linearized semiclassical Boltzmann equation in a minimal model of a doped circular NLS. We find that the toroidal geometry of the Fermi surface gives rise to two parametrically distinct Bloch-Grüneisen temperatures, associated with momentum transfers along the poloidal and toroidal directions, respectively. As a result, an intermediate temperature window opens between these two scales, in which the decay rate follows $\mathrm{\Gamma }\propto T^2$, while the conductivity follows $\sigma \propto T^{-2}$. We also obtain the low- and high-temperature asymptotic behaviors, and discuss implications for angle-resolved photoemission spectroscopy and transport measurements in candidate NLS materials.

Electron microscopy relies on the spatial coherence of electron beams to generate atomic-scale images using interference and diffraction, which can be degraded by inelastic-scattering processes that induce decoherence. Here, we present a theoretical study of decoherence arising from the electromagnetic interaction of free electrons with bulk materials and planar surfaces. We show that bulk plasmons dominate decoherence in Al and Au, while electronic excitations above the band gap, supplemented by weaker coupling to phononic and guided modes, are the primary channels in ionic insulators such as LiF. A thermal population of electromagnetic modes leads to a divergence in the energy-loss probability at low frequencies, which in turn produces a pronounced temperature dependence. We show that this effect can be exploited for nanoscale thermometry, predicting that optimized energy-filtered holography enables $\approx 0.1\%$ changes in fringe visibility for physically viable temperature variations in metals. Through these results, we establish a unified theoretical framework to describe free-electron decoherence in the bulk and surfaces of arbitrary materials.

We investigate an extended spin-full Su-Schrieffer-Heeger (SSH) model preserving chiral symmetry. It contains spin-mixing and nonmixing Rashba spin-orbit interactions, complex next to next nearest neighbor (NNNN) hopping. Using the theory of non-Hermitian matrices, we construct a Hamiltonian function facilitating exact analysis of the system. When the two types of Rashba interactions are present, the spectrum changes from band crossing to band touching having Dirac cone. The gap-closing condition for the spectrum and its symmetry is derived in detail. The phase diagram shows rich topological phases with winding number 1 or 2, re-entrant phase transitions, and multicritical points. An extension of the model to $\mathcal{M}$ coupled chains exhibits topological phases with winding number varying from one to $2\mathcal{M}$, and it is further characterized by the Zak phase. Remarkably, a domain-wall profile in nearest neighbor hopping can tune the location of mid-gap zero-energy states. The localization properties of the edge modes are characterized by the inverse participation ratio and compared with earlier works. Our model and method could bring a new perspective to certain classes of topological systems.

Ab initio downfolding describes the electronic structure of materials within a low-energy subspace, often around the Fermi level. Typically starting from mean-field calculations, this framework allows for the calculation of one- and two-electron interactions, and the parametrization of a many-body Hamiltonian representing the active space of interest. The subsequent solution of such Hamiltonians can provide insights into the physics of strongly correlated materials. While phonons can substantially screen electron-electron interactions, electron-phonon coupling has been commonly ignored within ab initio downfolding, and when considered, this is done only for short-range coupling. Here we propose a theory of ab initio downfolding that accounts for short- and long-range electron-phonon coupling on equal footing. Our practical computational implementation is readily compatible with current downfolding approaches. We apply our approach to polar materials MgO and GeTe, and we reveal the importance of both short-range and long-range electron-phonon coupling in determining the magnitude of electron-electron interactions. Our results show that in the static limit, phonons reduce the on-site repulsion between electrons by 40% for MgO and by 79% for GeTe. Our framework also predicts that overall attractive nearest-neighbor interactions arise between electrons in GeTe, consistent with superconductivity in this material.

We analyze a thermodynamically consistent model of Complementary metal-oxide-semiconductor-based ring oscillators near the onset of coherent voltage oscillations. For driving voltages close to the critical value, we derive the normal form of the Hopf bifurcation that underlies the oscillation transition in the thermodynamic limit. Using this normal form, we determine the phase and amplitude dynamics, and demonstrate that entropy dissipation decreases in the oscillating state for ring oscillators with more than three inverters. These findings culminate in a stability-dissipation relation, which links the observed decrease in dissipation to an increase in the local stability of the oscillating state. Next, we characterize finite-size fluctuations of the amplitude and phase near the critical voltage, using a stochastic version of the normal form. We demonstrate that close to the transition, finite-size fluctuations remain important at arbitrary system size, introducing oscillations even below the critical voltage. We further show that these noise-induced oscillations have an anomalously short decoherence time that scales sublinearly with the system-size, in contrast to the behavior far from criticality.

We study planar Josephson junctions formed on the surface of a three-dimensional topological insulator (Fu-Kane proposal). We examine the experimentally relevant parameter regimes in which the frequently used effective description in terms of two counter-propagating one-dimensional Majorana modes with hybridization dependent on the Josephson phase difference reaches its validity limit. This happens when the effective velocity of the emergent one-dimensional Majorana modes approaches zero. As parameters like the chemical potential or the width of the junction are tuned, instances of vanishing effective velocity mark the emergence of additional “Dirac cones” at zero energy and finite momentum. If the junction is subjected to an external magnetic field, Josephson vortices may then bind a number of zero modes in addition to the topological Majorana mode. The additional zero modes are “symmetry-protected” and can be lifted by a broken mirror symmetry (which is to be expected in realistic scenarios) as well as by an in-plane magnetization (or Zeeman field). We note that the ensuing presence of additional low-energy Andreev states can significantly contribute to measured quantities like the Josephson current or microwave absorption spectra.

We investigate the scaling and universality of the asymptotic behavior of nonequilibrium spin correlation functions in the presence of uncorrelated noise. In the noiseless case, these correlations exhibit an abrupt crossover from monotonic decay at fast sweep velocities to oscillatory behavior at slow sweeps. We show that stochastic driving not only shifts the associated critical sweep velocity, but also generates a finite momentum window of maximally mixed modes with $p_k=1/2$, which gives rise to a noise-induced highly oscillatory regime. Thus, noise does not merely suppress coherence, but can qualitatively reorganize the asymptotic correlation structure. We further show that the critical sweep velocity decreases with increasing noise strength, whereas the threshold velocity of the highly oscillatory regime increases, and that both phase boundaries scale linearly with the square of the noise intensity. Under the appropriate rescaling, all boundary curves collapse onto a single universal function. These results identify a universal mechanism by which stochastic driving creates dynamical structures in physically measurable spin correlations.

We analytically compute the thermal Hall conductance (THC) of fractional quantum Hall droplets under realistic conditions that go beyond the idealized linear edge theory with conformal symmetry. Specifically, we consider finite-size effects at low temperature, nonzero self-energies of quasiholes, and general edge dispersions. We derive measurable corrections in THC that are consistent with the experimental observables. Although the quantized THC is commonly regarded as a topological invariant that is independent of edge confinement, our results show that this quantization remains robust only for arbitrary edge dispersion in the thermodynamic limit. Furthermore, the THC contributed by Abelian modes can become extremely sensitive to finite-size effects and irregular confining potentials in any realistic experimental system. In contrast, non-Abelian modes show robust THC signatures under perturbations, indicating an intrinsic stability of non-Abelian anyons.