Shot noise at a conductance plateau in a quantum point contact (QPC) can be explained by considering equilibrations at the quantum Hall edges. The indication from recent experiments is that the charge equilibration length is much shorter than the thermal equilibration length. We discuss how this discovery gives rise to different thermal equilibration regimes in the presence of full charge equilibration. In this work, we classify these distinct regimes via dc current-current correlations (electrical shot noise) at definite experimentally found (or possible) QPC conductance plateaus for the edges of integer, particle-like, and hole-like filling fractions in a two dimensional electron gas. Our analyses show that distinct universal features arise among the different thermal equilibration regimes for the edges of particlelike and holelike states.

In this paper we present a theoretical examination of second-harmonic generation (SHG) in a graphene monolayer integrated within an attenuated total internal reflection (ATR) configuration. By embedding graphene in this optical setup, we explore the enhancement in the nonlinear optical response, particularly focusing on the efficiency of SHG. Our analysis reveals that the excitation of surface plasmon-polaritons (SPPs) plays a central role in significantly boosting the efficiency of SHG. The unique electronic properties of graphene, combined with the resonant characteristics of SPPs, create a synergistic effect that amplifies the nonlinear optical signals. This enhancement is attributed to the strong field confinement and the resonant nature of SPPs, which effectively increase the interaction between the incident light and the graphene monolayer. Furthermore, we analyze the underlying mechanisms that govern this process, providing a comprehensive theoretical framework that elucidates the interplay between graphene's electronic structure and the optical fields. Our findings suggest that the ATR scheme not only facilitates the excitation of SPPs but also optimizes the conditions for SHG.

Exceptional points (EPs) are spectral defects displayed by non-Hermitian systems in which multiple degenerate eigenvalues share a single eigenvector. This distinctive feature makes systems exhibiting EPs more sensitive to external perturbations than their Hermitian counterparts, where degeneracies are nondefective diabolic points. In contrast to these widely studied cases, more complex non-Hermitian degeneracies in which the eigenvectors are only partially degenerate are poorly understood. Here, we characterize these fragmented exceptional points (FEPs) systematically from a physical perspective, and demonstrate how they can be induced into the bulk and edge spectrum of two-dimensional and three-dimensional lattice models, exemplified by non-Hermitian versions of a Lieb lattice and a higher-order topological Dirac semimetal. The design of the systems is facilitated by an efficient algebraic approach within which we provide precise conditions for FEPs that can be evaluated directly from a given model Hamiltonian. The free design of FEPs significantly opens up a new frontier for non-Hermitian physics and expands the scope for designing systems with unconventional response characteristics.

Time-resolved x-ray absorption can reveal the dynamical screening of the local Coulomb interaction in strongly correlated photodoped materials. Here, we focus on the theoretical prediction of x-ray absorption in the presence of dynamical screening using the strong-coupling expansion, i.e., an expansion around the isolated absorption site in terms of the retarded interaction. The evaluation of higher-order diagrams is made numerically feasible by an approach based on the decomposition of the retarded interaction into complex exponentials. With this, we evaluate the strong-coupling series to third order on an electron-boson model of Holstein type. We demonstrate that in relevant coupling regimes, even low orders of the strong-coupling expansion can give a significant correction over the previously used lowest-order approximation.

We present an efficient implementation of the magnetic force theorem, which allows for direct evaluation of exchange parameters in $q$ space. The exchange parameters are calculated directly from Bloch states and the implementation does not rely on any mapping onto localized orbitals. This renders the approach well suited for high-throughput computations, where the construction of a localized basis set—for example, Wannier functions—often is impractical. We demonstrate the versatility of the method by applying it to yttrium iron garnet, where we obtain excellent agreement with the experimental magnon dispersion and Curie temperature without any prior assumptions of important exchange pathways. In particular, the calculations reveal the existence of several inequivalent exchange pathways associated with the same interatomic distances. Performing such calculations in $q$ space fully accounts for long-range exchange interactions and provides a convenient route for validating models obtained by fitting to inelastic neutron scattering data.

Cuprate superconductors have attracted extensive attention due to high critical temperatures. Conventional cuprates typically contain perfect ${\mathrm{CuO}}_2$ planes, which are considered as a key factor to superconductivity since the superconductivity takes place in them. However, in ${\mathrm{Ba}}_2{\mathrm{CuO}}_{3+\delta }$ with $\delta =0.2$ and O-depleted ${\mathrm{CuO}}_2$ planes, superconductivity still arises even with a transition temperature as high as 73 K. Using combined density functional theory and dynamical mean-field theory calculations, we investigated the electronic correlation and electronic structure of ${\mathrm{Ba}}_2{\mathrm{CuO}}_{3.25}$ with alternating quasi-one-dimensional (quasi-1D) CuO planes and O-depleted ${\mathrm{CuO}}_2$ planes. We find that although different from the usual cuprates, the Cu atoms are still dominated by a $3d^9$ configuration and the system is of a new kind of correlated single-orbital physics. The quasi-1D CuO planes, composed of parallel Cu-O chains, are slightly hole-doped quasi-1D Mott insulators, while the O-depleted ${\mathrm{CuO}}_2$ planes are more hole doped, with a two-dimensional correlated electronic structure, and may host superconductivity.

We theoretically investigate a model with electrons and holes whose Fermi surfaces are perfectly nested. The fermions are assumed to be interacting, both with each other and with the lattice. To suppress inhomogeneous states, a sufficiently strong long-range Coulomb repulsion is included into the model. Using the mean field approximation, one can demonstrate that, in the absence of doping, the ground state of such a model is insulating and possesses a density-wave order, either spin-density wave or charge-density wave. Upon doping, a finite ferromagnetic polarization emerges. It is argued that the mechanism driving the ferromagnetism is not of the Stoner type. A phase diagram of the model is constructed and various properties of the ordered phases, such as half-metallicity and cone magnetic structure, are studied.

Rydberg atom arrays promise high-fidelity quantum simulations of critical phenomena with flexible geometries. Yet, experimental realizations inevitably suffer from disorder due to random displacements of atoms, leading to departures from the expected behavior. Here, we study how such positional disorder influences the Ising criticality. Since disorder breaks the ${\mathbb{Z}}_2$ symmetry, one might expect the system to flow to an infinite-strength disordered fixed point, erasing all nontrivial critical features in low spatial dimensions. Remarkably, we find instead that disorder in Rydberg systems is subjected to nontrivial local constraints, making the physics markedly different from systems with more conventional spatially short-range correlated or long-range correlated disorder. This leads to new classes of criticalities even at dimensions where conventional disorder would destroy criticality altogether. We then demonstrate as a consequence how a pseudocriticality emerges in Rydberg atom chains of experimentally realistic scale, and show that the renormalization group flow is governed by a locally constrained ${\mathbb{Z}}_2$-breaking perturbation. Our findings uncover disorder-driven phenomena and underscore the importance of carefully treating disorder effects in quantum simulators.

The study of symmetry restoration has recently emerged as a fruitful means to extract high-level information on the relaxation of quantum many-body systems. However, while the restoration of internal symmetries has been investigated intensively, that of spatial symmetries has hitherto only been considered in the context of random unitary circuits. Here, we present a complementary study of translation symmetry restoration in integrable systems. In particular, we consider a one-dimensional chain of spinless, noninteracting fermions quenched from a $\nu >1$ shift invariant state, and follow the local restoration of one-site shift invariance using the Frobenius distance $\mathrm{\Delta }{F}_A$ between the state on a subsystem and its symmetrized counterpart. Distinct from the case of random unitary circuits, where symmetry restoration occurs abruptly for times proportional to the subsystem size, we find that symmetry here is restored smoothly and over timescales of the order of the subsystem size squared. We also find that the so-called ‘‘quantum Mpemba effect’’ is readily observed. Most importantly, we show that—in contrast to the case of continuous internal symmetries—this discrete symmetry restoration is not qualitatively described by a quasiparticle picture for $\mathrm{\Delta }{F}_A$, and therefore goes beyond the hydrodynamic description. Our results can be directly extended to higher dimensions.

Two-dimensional (2D) materials hosting color centers and spin defects are emerging as key platforms for quantum technologies. However, the impact of reduced dimensionality on the spin-lattice relaxation time ($T_1$) of embedded defect spins—critical for quantum applications—has remained largely unexplored. In this study, we present a systematic first-principles investigation of the negatively charged boron-vacancy (${\mathrm{V}}_{\text{B}}^{-}$) defect in monolayer boron nitride (BN), as well as in ${\mathrm{AA}}^{\prime }$-stacked hexagonal BN (hBN) and ABC-stacked rhombohedral BN (rBN). Our results reveal that the $T_1$ times of ${\mathrm{V}}_{\text{B}}^{-}$ in monolayer BN and hBN are nearly identical at room temperature. Surprisingly, despite the symmetry reduction in rBN that opens additional spin relaxation channels, ${\mathrm{V}}_{\text{B}}^{-}$ exhibits a longer $T_1$ compared to hBN. We attribute this effect to the stiffer out-of-plane phonon modes in rBN, which activate spin-phonon relaxation at reduced strength. These findings suggest that ${\mathrm{V}}_{\text{B}}^{-}$ in rBN offers enhanced spin coherence properties, making it a promising candidate for quantum technology applications.

We investigate space-time coherence in one-dimensional lattices of exciton-polariton condensates formed by fully reconfigurable nonresonant optical pumping. Starting from a driven-dissipative Gross-Pitaevskii equation with deterministic reservoir kinetics and stochastic condensate noise, we derive a discrete complex-field model that incorporates coherent tunneling, reservoir-mediated dissipative coupling, and gain-saturation nonlinearity. The combination of these mechanisms, playing a crucial role in synchronization of driven-dissipative polariton condensate lattices, provides a multidimensional parameter space, allowing controllable switching between Kardar-Parisi-Zhang (KPZ) and Edward-Wilkinson (EW) dynamics. Adiabatic elimination of fast density fluctuations reveals a wedge-shaped region in the complex hopping plane where the coarse-grained phase dynamics reduces to the KPZ equation. By computing high-resolution phase diagrams of the temporal and spatial scaling exponents we pinpoint the boundaries separating the KPZ domain from the EW regime. Large-scale graphics processing unit (GPU) simulations of chains containing up to $N=2000$ condensates confirm these predictions: inside the wedge the exponents converge to ${\beta }_N=\mathbf{0}.\mathbf{329}\left(3\right)\approx 1/3$ and ${\chi }_N=\mathbf{0}.\mathbf{504}\left(4\right)\approx 1/2$, whereas outside it the dynamics moves away from KPZ and ultimately flow toward the EW fixed point, although finite system size and finite observation time may yield intermediate effective exponents.

We develop a theoretical framework for the transport of spin angular momentum and linear momentum carried by magnons in electrically insulating collinear antiferromagnets (AFs). Focusing on both transverse and longitudinal nonlocal geometries, we model magnons as a viscous fluid and examine the hydrodynamic regime that arises when the momentum-conserving magnon-magnon scattering length is shorter than the momentum-relaxation length associated with momentum-nonconserving processes. The hydrodynamic regime in these two geometries is marked by distinct flow patterns: vortex structures in the transverse setup and Poiseuille flow in the longitudinal setup. We show that scattering between magnon modes carrying opposite spin angular momentum induces draglike effects, significantly altering magnon spin current propagation in AFs. Furthermore, we uncover mode-dependent transport regimes at specific distances by tuning the magnetic field, which enables selective control of viscous and diffusive transport in individual magnon modes. Our results position AFs as a promising platform for realizing magnon-fluid dynamics and studying collective spin transport phenomena.

The origin of charge transport and magnetization anisotropy was studied in ${\mathrm{DyB}}_{12}$, an antiferromagnetic (AF) metal with Néel temperature $T_{\mathrm{N}}\approx 16.3$ K that exhibits both small, static Jahn-Teller distortions of the fcc lattice and nanoscale electronic instabilities (dynamic charge stripes). The magnetic field (H) versus temperature (T) phase diagrams were constructed. Moreover, using the angular ϕ dependences of magnetoresistance and magnetization, butterfly-type patterns of the H-ϕ magnetic phase diagram in the (110) plane were created, including a number of different magnetic phases separated from each other by radial and circular boundaries. Several positive and negative contributions to magnetoresistance were separated and analyzed, providing arguments in favor of the important role of the spin density wave $5d$ component in the magnetic structure of the antiferromagnetic state. We argue that charge fluctuations in stripes are responsible for the suppression of the Ruderman-Kittel-Kasuya-Yosida indirect exchange between the nearest neighbor $\mathrm{D}{\mathrm{y}}^{3+}$ ions located along the same $\langle 110\rangle$ directions, as these dynamic charge stripes produce the magnetic phase diversity and the butterfly-type anisotropy in ${\mathrm{DyB}}_{12}$.

Optically active paramagnetic point defects in host semiconductors hold significant potential for integration into quantum technologies. However, the identification of a suitable candidate from the vast search space of numerous structural configurations, along with charge and spin states of defects, even within a single host, is extremely challenging. Here, we have developed a high-throughput approach based on first-principles calculations to screen group-IV-related promising quantum defects in 4H-SiC. We have systematically selected 13 quantum defects based on desired thermodynamic, electronic, and optical screening criteria. This strategy successfully identifies seven novel group-IV-related defects with single-photon emission within the telecommunication and midinfrared window, with a zero phonon line energy exceeding 0.4 eV. Two ${\mathrm{Sn}}_{\text{Si}}{\mathrm{V}}_{\text{C}}$ defects have favorable emission for silica fiber-based optical communication, while the remaining group-IV defects hold promise for fluoride fiber-based and free space communication. These quantum defects possess a strong transition dipole moment surpassing 5 Debye and exhibit zero-field splitting within the microwave range, and hence are potential for quantum sensing and spin-photon interfaces.

Prethermalization phenomena in driven systems are generally understood via a local Floquet Hamiltonian obtained from a high-frequency expansion. Remarkably, recently it has been shown that a driven Kitaev spin liquid with fractionalized excitations can realize a quasistationary state that is not captured by this paradigm. Instead distinct types of fractionalized excitations are characterized by vastly different temperatures—a phenomenon dubbed fractionalized prethermalization. In our work, we analyze fractionalized prethermalization in a driven one-dimensional Hubbard model at strong coupling which hosts spin-charge fractionalization. At intermediate frequencies quasisteady states emerge which are characterized by a low spin and high charge temperature with lifetimes set by two competing processes: the lifetime of the quasiparticles determined by Fermi's Golden rule and the exponentially long lifetime of a Floquet prethermal plateau. We classify drives into three categories, each giving rise to distinct (fractional) prethermalization dynamics. Resorting to a time-dependent variant of the Schrieffer-Wolff transformation, we systematically analyze how these drive categories are linked to the underlying driven Hubbard model, thereby providing a general understanding of the emergent thermalization dynamics. We discuss routes toward an experimental realization of this phenomenon in quantum simulation platforms.

Exceptional points (EPs), singularities in non-Hermitian systems where eigenvalues and eigenstates coalesce, exhibit a dramatically enhanced response to perturbations compared to Hermitian degeneracies. This makes them exceptional candidates for sensing applications. The spectral splitting of an $N\mathrm{th}$-order EP scales with perturbation strength $\epsilon$ over a wide range, from $\epsilon$ to ${\epsilon }^{1/N}$. Although the exact scaling exponent can be determined, in principle, by solving the characteristic equation, this approach becomes analytically intractable for large $N$ and often fails to yield useful physical insight. In this work, we develop a theory to directly predict the scaling exponent from the matrix positions of the perturbation. By using the Jordan block structure of the unperturbed Hamiltonian, we show that the splitting exponent can be analytically determined when the matrix positions of the perturbation satisfy some specific conditions. Our analytical framework provides a useful design principle for engineering perturbations to achieve a desired spectral response, facilitating the development of EP-based sensors.

The interplay between magnetic ordering and band topology has emerged as a fertile ground for discovering novel quantum states with profound implications for fundamental physics and next-generation electronics. Here, we theoretically predict a different type-III Weyl semi-half-metal (SHM) state in monolayer ${\mathrm{Li}}_2\mathrm{N}$, uniquely combining magnetic half-metallicity and type-III Weyl semimetal characteristics. First-principles calculations reveal a fully spin polarized and critically tilted Weyl cone around the Fermi level in monolayer ${\mathrm{Li}}_2\mathrm{N}$, driven by $p$-orbital ferromagnetism. This arises from the symmetry-protected band crossing between a partially flat valence band and a highly dispersive conduction band, leading to type-III Weyl fermions with strong transport anisotropy. A low-energy $k·p$ Hamiltonian is constructed and corresponding nontrivial edge states are uncovered to capture the topological nature of ${\mathrm{Li}}_2\mathrm{N}$. Notably, this Weyl SHM phase remains robust under biaxial strain ranging from $-2\%$ to $4\%$, with an ideal type-III Weyl fermion emerging alongside a linelike ergodic surface emerging at $3.7\%$ strain, offering a promising platform for exploring correlated electronic phenomena. Our results establish ${\mathrm{Li}}_2\mathrm{N}$ as a viable candidate for realizing exotic type-III Weyl SHM states and open an avenue for exploring the intricate interplay among magnetism, topology, and flat-band physics.

Competing superconducting (SC) and density-wave orders are of key importance in generating unconventional superconductivity and emergent electronic responses. Quasi-one-dimensional models provide insight into these competing orders and suggest higher-dimensional realizations through coupled-wire constructions, but analysis of such systems remains limited. Recent studies suggest that double-helical edge states in double quantum spin Hall insulators form a two-channel Luttinger liquid that exhibits SC and spin density wave (SDW) phases and their $\pi$-junction analogs. Here, we analyze weakly coupled double-helical edge states from the surface of a periodically stacked layered structure consisting of double quantum spin Hall insulators and dielectrics, where interedge interactions approximately develop a tunable helical sliding Luttinger liquid (HSLL) order. Using a renormalization-group analysis, we construct phase diagrams and identify a regime of HSLL parameters that favor competing two-dimensional $\pi$-SC and $\pi$-SDW orders. We identify parameter regimes where the competing orders could be realized experimentally in nanoscale devices. Our study suggests a promising materials platform for exploring tunable $\pi$-SC and $\pi$-SDW orders in double quantum spin Hall superlattices.