Flat bands (FBs) play a crucial role in condensed matter physics, offering an ideal platform to study strong correlation effects and enabling applications in diffraction-free photonics and quantum devices. However, the study and application of FB properties are susceptible to interference from dispersive bands. Here, we explore the impact of a type of experimentally controllable dissipation on systems hosting both flat and dispersive bands by calculating the steady-state density matrix. We demonstrate that such dissipation can drive particles from dispersive bands into FBs and establish the general conditions for this phenomenon to occur. Our results demonstrate that dissipation can eliminate the influence of dispersive bands, thereby facilitating FB preparation, property measurement, and utilization. This opens a new avenue for exploring FB physics in open quantum systems, with potential implications for strongly correlated physics.

Complex oxides are well-known to develop oxygen ordering patterns with well-defined periodicities, but their interplay with the electronic structure remains largely unexplored. Here, we report resonant and nonresonant x-ray diffraction data indicating a four-unit-cell periodic superstructure related to oxygen vacancy ordering in ${\mathrm{La}}_{2-x}{\mathrm{Ca}}_x{\mathrm{CuO}}_{4-\delta }$ films with Ca dopant concentrations from the underdoped ($x=0.15$) to the extremely overdoped ($x=0.50$) regime. Whereas the oxygen superstructure is temperature independent up to 300 K, a strongly temperature-dependent electronic charge density wave (CDW) is observed in the underdoped and slightly overdoped regimes ($x\le 0.20$). The periodicity, in-plane, and out-of-plane correlation lengths of the CDW are locked in by the oxygen superstructure. Our results highlight the interdependence of electronic and atomic ordering phenomena and underscore the necessity of determining the temperature dependence to distinguish electronic and lattice atomic contributions to superstructures.

The $\mathrm{SU}\left(N\right)$ Hubbard model is a natural extension of the $\mathrm{SU}\left(2\right)$ model. However, even the $N=3$ case remains poorly understood. We report a ground-state phase diagram of the square lattice $\mathrm{SU}\left(3\right)$ Fermi-Hubbard model. Using a backflow Ansatz, we identify strong signatures of a Mott transition and a subsequent magnetic transition, and the suppression of a previously predicted magnetic phase. We study the hole-doped model, identifying a transition from magnetic to paramagnetic behavior in the strong-coupling regime. Our findings offer a different ground-state picture. More broadly, our work suggests a path to study general $\mathrm{SU}\left(N\right)$ Hubbard models with arbitrary filling and geometry.

Rashba spin-orbit coupling (RSOC) induces strong momentum-dependent spin splitting and plays a crucial role in fields such as spintronics and topological photonics. We here theoretically investigate the collective excitations in monolayer transition-metal dichalcogenides (ML-TMDs) hosting RSOC, and conceive an approach to precisely quantify the strength of RSOC using plasmons. We determine the electron energy loss function (EELF) and plasmon dispersions for $n$-type ML-TMDs from the dynamic dielectric function in the framework of the standard random phase approximation. In this system, both optical and acoustic plasmon modes are observed in the EELF and plasmon dispersions. Moreover, the plasmonic and spectral properties are tunable by electron density and dependent on RSOC. Crucially, we identify a minimum energy gap between the two plasmon modes to serve as a direct spectral signature of the RSOC strength. These results establish plasmons as a noninvasive, precise, and broadly tunable technique for determining RSOC in TMD van der Waals heterostructures and devices.

Excitonic states of tightly bound electron-hole pairs dominate the optical response in a growing class of two-dimensional (2D) materials and their van der Waals (vdW) heterostructures. In transition metal dichalcogenides (TMDs) a useful guidance for the excitonic spectrum is the analogy with the states in the 2D hydrogen atom. From our symmetry analysis and solving the Bethe-Salpeter equations we find a much richer picture for excitons and predict their tunable resonant $s-p$ mixing. The resonance is attained when the sub-band splitting matches the energy difference between the $1s$ and $2p_{+}$ (or $2p_{-}$) excitons, resulting in the anticrossing of the spectral lines in the absorption as a function of the sub-band splitting. By focusing on TMDs modified by magnetic proximity, and gated 3R-stacked bilayer TMD, we corroborate the feasibility of such tunable spin splitting. The resulting tunable and bright $s-p$ excitons provide unexplored opportunities for their manipulation and enable optical detection of Rashba or interlayer coupling in vdW heterostructures.

Dynamical constraints in many-body quantum systems can lead to Hilbert space fragmentation, wherein the system's evolution is restricted to small subspaces of Hilbert space called Krylov sectors. However, unitary dynamics within individual sectors may also be slow or nonergodic, which limits experiments' ability to measure the properties of the entire sector. We show that additional controlled dephasing reliably mixes the system within a single Krylov sector, and that simple observables can differentiate these sectors. For example, in the strongly interacting XXZ chain with dephasing, the spin imbalance between even and odd sublattices distinguishes sectors. For appropriate choices of initial states, the imbalance begins positive, decays to a negative minimum value at intermediate times, and eventually returns to zero. The minimum reflects the average imbalance of the Krylov sector associated to the initial state. We compute the size of the minimum analytically in the limit of strong interactions, and validate our results with simulations at experimentally relevant interaction strengths.

We investigate spin-dependent transport phenomena in epitaxially grown ${\mathrm{Fe}}_3\mathrm{Si}$ films, focusing on the anisotropic magnetoresistance (AMR), planar Hall effect (PHE), anomalous Hall effect (AHE), and spin Hall effect (SHE). While the sign and magnitude of the AMR and PHE depend on the current orientation relative to the crystallographic axes, the AHE and SHE remain nearly independent of the current orientation. The current orientation dependence of the AMR and PHE is consistent with the phenomenological theory of galvanomagnetic effects, where the resistivity tensor can be expanded in terms of magnetization components with coefficients determined by crystal symmetry. These findings suggest the distinct interplay between symmetry, band structure, and magnetization in the spin-dependent transport phenomena.

We theoretically investigate the current-enabled linear optical conductivity of collective modes in superconductors with unconventional pairing symmetries. After deriving general formulas for the optical conductivity of a superconductor featuring multiple pairing channels and bands using the path integral formalism, we apply these formulas to several models. Using a model of competing $s$- and $d$-wave pairing interactions, we find that several known collective modes generate peaks in the optical conductivity upon injection of a supercurrent. This includes single- and multiband versions of Bardasis-Schrieffer modes, mixed-symmetry Bardasis-Schrieffer modes, and Leggett modes. Using a model for interband $p$-wave superconductivity with Rashba spin-orbit coupling, we find that in such a system Bardasis-Schrieffer modes are optically active even without the introduction of a supercurrent. In a $p+ip$ chiral ground state, these modes can produce peaks in the longitudinal and transverse optical conductivity. Other collective modes belonging to the chiral $p+ip$ order parameter are unaffected by the spin-orbit coupling but contribute to the optical response when a supercurrent is introduced. These results promise avenues for the observation of collective modes in a variety of superconducting systems, including multiband superconductors and superconductors that feature multiple pairing channels or multicomponent order parameters, such as chiral $p$- or $d$-wave superconductors.

Thiospinel ${\mathrm{Co}}_{1.3}{\mathrm{Ir}}_{1.7}{\mathrm{S}}_4$ is a rare diamond-lattice antiferromagnetic insulator with a relatively high Néel temperature of $T_{\mathrm{N}}\sim 290$ K at ambient pressure. We report here a systematic study of the pressure dependence of the structural, transport, and magnetic properties of ${\mathrm{Co}}_{1.3}{\mathrm{Ir}}_{1.7}{\mathrm{S}}_4$ up to 12 GPa. Below 5 GPa, ${\mathrm{Co}}_{1.3}{\mathrm{Ir}}_{1.7}{\mathrm{S}}_4$ retains its insulating behavior, with $T_{\mathrm{N}}$ initially increasing and then decreasing, accompanied by a gradual reduction in the band gap. At $P\sim 6$ GPa, an insulator-to-metal transition occurs. In the pressure range of $7\text{GPa}\le P\le 10$ GPa, ${\mathrm{Co}}_{1.3}{\mathrm{Ir}}_{1.7}{\mathrm{S}}_4$ exhibits a metallic state, with the resistivity showing a broad hump likely corresponding to short-range magnetic order. Above 10.5 GPa, it further evolves into a normal metal, suggesting the disappearance of magnetism. No structural distortion is detected across the sequential insulator-to-metal and magnetism-suppression transitions associated with the two-step phase evolution of the Mott transition. Density-functional theory calculations capture the key experimental trends, highlighting the crucial role of bandwidth and electronic correlations evolution under pressure in driving the Mott transition. A magnetism-pressure phase diagram for ${\mathrm{Co}}_{1.3}{\mathrm{Ir}}_{1.7}{\mathrm{S}}_4$ has been established, wherein the absence of quantum critical behavior implies that the bandwidth-controlled Mott transition may proceed as a first-order transition. Our results advance the broader understanding of pressure-induced quantum phase transitions in diamond-lattice antiferromagnets.

We study a quasiperiodic model in one dimension, namely the extended Aubry-André-Harper (EAAH) chain, that realizes a critical phase comprising entirely single-particle critical states in the noninteracting limit. In the presence of short-range interactions, the noninteracting critical phase transforms to a many-body critical (MBC) phase, separated by lines of MBC-ergodic, MBC-many-body localized (MBL) and ergodic-MBL phase transitions that meet at a triple point. We elucidate the unusual characteristics of the MBC phase compared to the ergodic and MBL phases through the localization properties of the excitations in real space and Fock space (FS), and the eigenstate inverse participation ratio (IPR). We show that the MBC phase, like the MBL phase, is well described by a multifractal scaling of the IPR and a linear finite-size scaling ansatz near the transition to the ergodic and MBL phases. However, the MBC phase, at the same time, exhibits delocalization of all single-particle excitations and a system-size-dependent Fock-space localization length, analogous to the ergodic phase. Remarkably, we find evidence of unusual Widom lines on the phase diagram in the form of lines of pronounced peaks or dips in the FS localization properties inside the MBC and MBL phases. These Widom lines either emerge as a continuation of the precursor phase transition line terminating at the triple point, or originate from a phase boundary.

Time-resolved photoemission spectroscopy provides a unique and direct way to explore the real-time nonequilibrium dynamics of electrons and holes. The formal theory of spectral function evolution requires inclusion of electronic correlations and dissipation, which are challenging due to the associated long simulation timescales which translate to a high computational cost. Recent methodological developments, namely, the real-time Dyson expansion, as well as theoretical developments of many-body perturbation theory for dissipative systems, have allowed for the study of driven-dissipative interacting quantum systems. In this work, we implement the hitherto unrealized study of driven dynamically correlated systems and utilize these methods and perturbative expansions. We illustrate the combined formalism on a prototypical two-band semiconductor model with long-range density-density Coulomb interactions. We show that the intraband thermalization of conduction band electrons induces nontrivial time-dependent changes in the system's band structure and a time-evolving band-gap renormalization (with a reduction by up to 8.4%). We show that the qualitative features are preserved for a variety of parameters, discuss the corresponding spectral dynamics, and provide an outlook on the introduced simulation framework, which enables treating electron-electron scattering and dissipation effects on equal footing.

Two-dimensional materials offer unique opportunities for manipulating light-matter interactions at the nanoscale. Phosphorene, a single layer of black phosphorus, possesses a tunable band gap and strong in-plane anisotropy, leading to pronounced linear dichroism. Hexagonal boron nitride (hBN) is a wide band gap van der Waals dielectric with inherent anisotropy and a hyperbolic dispersion in the mid infrared. While both materials have been studied extensively in isolation, how their combined optical responses evolve in a phosphorene/hBN heterostructure is not yet fully understood. Here we demonstrate that phosphorene/hBN heterostructures exhibit markedly different reflection and absorption spectra compared to their individual components. In particular, we identify a robust, polarization insensitive absorption peak near the in-plane transverse optical phonon frequency of hBN. Conversely, the absorbance near the in-plane and out-of-plane longitudinal optical phonon frequencies can be tuned by varying the phosphorene surface conductivity, giving rise to polarization sensitive resonances. We further show that, for transverse electric (TE) and transverse magnetic (TM) polarized light, the absorbance evolves in opposite directions as the incidence angle changes. Our findings clarify the underlying optical interactions in phosphorene-hBN layered structures and significantly enhance the potential for designing advanced polarization-based optoelectronic devices.

In this work, we investigate impurity-induced Friedel oscillations in the doped two-dimensional Hubbard model, focusing on the role of holon and doublon excitations. We show that weak impurities, due to the nonfermionic nature of the underlying quasiparticles, induce Friedel oscillations whose behavior is consistent with an effective noninteracting theory for these quasiparticles and whose wave vector reflects the violation of Luttinger's theorem. At larger impurity strength, the system transitions to a phase-separated state composed of coexisting Mott-insulating (half-filled) and hole-rich regions. Within the composite operator framework, this phase separation arises from a competition between the kinetic energy of holons and the tendency to form tightly bound holon-doublon pairs. Our results offer insights into the nature of charge carriers and the emergent electronic phases in the doped Mott regime.

The Haldane model is a standard tight-binding model describing electrons hopping on a hexagonal lattice subject to a transverse, dipolar magnetic field. We consider its interacting version for values of the interaction strength that are small compared to the bandwidth. We study the critical case at the transition between the trivial and “topological” insulating phases, and we rigorously establish that the transverse conductivity on the dressed critical line is quantized at a half-integer multiple of $e^2/h$: this is the average of the integer values of the Hall conductivity in the insulating phases on either side of the dressed critical line. Together with previous results, this fully characterizes the nature of the phase transition between different Hall plateaus and proves its universality with respect to many-body interactions. The proof is based on a combination of constructive renormalization group methods and exact lattice Ward identities.

We investigate the spin properties of InAs/InGaAs/InP quantum dots grown by metalorganic vapor-phase epitaxy (MOVPE) deposition using droplet epitaxy, which emits in the telecom C band. Using pump-probe Faraday ellipticity measurements, we determine electron and hole $g$ factors of $|g_e|=0.93$ and $|g_h|=0.47$, with the electron $g$ factor being nearly twice as low as typical molecular beam epitaxy Stranski-Krastanov (SK) grown samples. Most significantly, we measure a longitudinal spin relaxation time $T_1=3.0\mu \mathrm{s}$, representing an order of magnitude improvement over comparable MBE SK grown samples. Despite significant electron $g$-factor anisotropy, we observed that it is reduced relative to similar material composition samples grown with MBE or MOVPE SK methods. We attribute this $g$-factor anisotropy and spin lifetime improvements to the enhanced structural symmetry achieved via MOVPE droplet epitaxy, which mitigates the inherent structural asymmetry in strain-driven growth approaches for InAs/InP quantum dots. These results demonstrate that MOVPE droplet epitaxy-grown InAs/InGaAs/InP quantum dots exhibit favorable spin properties for potential implementation in quantum information applications.

We have theoretically studied the $G$ center in bulk silicon material using the empirical tight-binding model for calculations of unfolded band structures with configuration interaction correction for the exciton at $\mathrm{\Gamma }$ point of the Brillouin zone. The $G$ center in B configuration (emissive) being a candidate structure as the telecom single- and entangled-photon source has two substitutional carbons and one interstitial atom embedded into the bulk in six equally possible configurations. Taking advantage of the low computation effort of the tight-binding and unfolding approaches, it is possible to calculate and analyze the behavior of a variety of electronic configurations. Our tight-binding model is able to describe not only the behavior of the $G$ center in the silicon bulk but using the unfolding approach, it can also pinpoint the contributions of different elements of the supercell on the final pseudoband structure. Moreover, the configuration interaction correction with single-particle basis states computed by our unfolded tight-binding model predicts a very small fine-structure splitting of the ground state exciton, both for bright and dark doubletes, in the studied system. That underscores the possibility of the silicon $G$ center to become a very good emitter of single and entangled photons for quantum communication and computation applications.

We propose a ${\sigma }_z$-symmetry-preserving strategy to realize Janus bound states in the continuum (Janus BICs) exhibiting asymmetric topological charges in upward and downward radiation channels. Unlike the prior approach that typically involve explicit structural perturbations to break vertical symmetry, our design employs bilayer photonic crystals (PCs) with independently tunable refractive index (RI), enabling optical asymmetry without altering the geometric symmetry. In the optically symmetric case, the system supports symmetry-protected BICs at $\mathrm{\Gamma }$ point with topological charge $q=-1$ and accidental BICs at off-$\mathrm{\Gamma }$ point with $q=+1$. Upon introducing RI detuning, the polarization vortex splits into two circularly polarized states (C points) with half-integer topological charge ($q=+1/2$), shifting oppositely in momentum space for upward and downward radiation, while the symmetry-protected BICs remain unaffected. Janus BICs emerge through the migration of upward-radiating C points toward the $\mathrm{\Gamma }$ point, accumulating a total topological charge of $q=+1$, while the downward-radiating counterpart contributes $q=-1$, leading to a net topological charge reversal between the two radiation channels. We further investigate the robustness of Janus BICs against variations in RI contrast and structural perturbations, demonstrating their stable existence over a broad parameter range. The experimental feasibility of this configuration is also examined when considering substrates, proposing two practical implementation schemes and validating one of them through numerical simulations. This purely optical asymmetry mechanism enables the realization of Janus BICs without any structural deformation, offering a platform for directional light sources, chiral photonic interfaces, and integrated topological photonics.