Periodically driven systems provide unique opportunities to investigate the dynamics of topological excitations far from equilibrium. In this paper, we report a time-crystalline soliton (TCS) state in a driven-dissipative ${\varphi }^4$ model. This state exhibits spontaneous breaking of discrete time-translational symmetry while simultaneously displaying spatial soliton behavior. During time evolution, the soliton pattern periodically oscillates between kink and antikink configurations. We further study TCS dynamics under noise, demonstrating that soliton random walk can induce a dynamical transition between two distinct $Z_2$ symmetry-breaking time-crystalline phases in time domain. Finally, we examine the annihilation of two spatially separated TCSs under noise. Importantly, in contrast to the confined behavior of time-crystalline monopoles reported in Yue and Cai [Phys. Rev. Lett. 131, 056502 (2023)], the dynamics of time-crystalline solitons is deconfined despite the nonequilibrium nature of our model: the statistically averaged annihilation time scales as a power law with the solitons' initial separation.

We theoretically study terahertz pump-probe experiments in $h\mathrm{BN}$ from the perspective of Floquet optical materials and photonic time crystals. The anisotropic nature of this material results in a large separation of frequencies of in-plane and out-of-plane optical phonons and leads to several branches of phonon-polariton excitations. We consider a slab of finite thickness pumped at the frequency of middle polaritons, around 25 THz. We theoretically analyze properties of the pump induced state and identify several interesting features, including possible light amplification and parametric instability at 2 THz. We relate these features to resonant pair scattering processes of polaritons excited by the pump pulse. We show that amplification/instability frequency ranges depend on both the pump intensity and the slab thickness. We point out that this setup can be utilized to strongly enhance optical nonlinearities at terahertz frequencies. Richness and tunability of this system suggest that it holds promise for practical applications in terahertz technology.

Excitation and control of antiferromagnetic magnon modes lie at the heart of coherent antiferromagnetic spintronics. Here, we propose a topological surface magnon-polariton as a new approach in the prototypical magnonic material hematite. We show that in an insulating canted antiferromagnet, where strong-coupled magnon-photon modes can be achieved using on-chip microwave layouts, a surface magnon-polariton mode exists in the gap of the bulk magnon-photon bands. The emergence of surface magnon-polariton mode is further attributed to the nontrivial topology of bulk magnon-photon bands. Magnon-photon coupling enhances the Berry curvature near the anticrossing points, leading to a topological bulk Chern band associated with the surface magnon-polaritons. Our work provides a general principle for the utilization of optomagnetic properties in antiferromagnets, with an illustration of its experimental feasibility and wide generality as manifested in hematite.

Nematic aerogel (nAG) supports so-called polar phase in liquid ${}^3\mathrm{He}$. The experiments [Dmitriev et al., JETP Lett. 112, 780 (2020)] showed that the onset of polar phase inside the nAG is accompanied by emergence of a sound wave with frequency quickly growing with cooling down from transition temperature and reaching a plateau. To describe this behavior, we start by calculating the elastic properties of the dry nematic AG that appear to depend only on Young's modulus of the parent material (e.g., mullite), the volume fraction of the solid phase $\psi (=5\%)$ and the aspect ratio of the representative volume of nAG. The elastic constants are then used to solve elastohydrodynamic equations for various sound vibrations of nAG filled with ${}^3\mathrm{He}$. The (isotropic) first sound and anisotropic second sound in the polar phase are strongly hybridized with fourth sound and standard elastic modes in nAG. The hybrid second and the transverse fourth sound start with zero velocity at the transition, similar to pure ${}^3\mathrm{He}$, and quickly grow with lowering temperature until they hit the sample finite size cutoff.

The attractive Hubbard model plays a paradigmatic role in the study of superconductivity (superfluidity) and has become directly realizable in ultracold atom experiments on optical lattices. However, the critical temperatures, $T_c$'s, remain lower than the lowest temperatures currently achievable in experiments. Here, we explore a possible route to enhance $T_c$ by introducing an additional next-nearest neighbor (NNN) hopping, $t^{\prime }$, in a two-dimensional square lattice. We perform sign problem-free determinant quantum Monte Carlo simulations to compute response functions such as pairing correlation functions, superfluid density, and uniform spin susceptibility. Our results show that a judicious choice of $t^{\prime }$ can increase $T_c$ by up to $50\%$ compared to the case with only nearest neighbor hopping. In contrast, the preformed pairs' temperature scale, named pairing temperature, $T_p$, decreases with increasing $|t^{\prime }/t|$, which should represent a reduction of the pseudogap region, favoring a more BCS-like behavior at intermediate coupling. We further analyze the interacting density of states to characterize the transition from a pseudogap regime to a fully gapped superconducting state. These findings suggest that NNN hopping could be a viable route to increase $T_c$ to values closer to experimentally accessible temperature scales.

Non-Fermi liquids in dimensions $d>2$ remain poorly understood, particularly when relevant perturbations destabilize them. A prominent example is the overscreened Kondo fixed points in impurity models, and their one-dimensional analogs known as chirally stabilized fixed points. While such models can potentially host non-Abelian anyons, their extension to genuinely higher-dimensional, topologically ordered states has lacked a controlled framework. Here we develop a Wilsonian operator-product-expansion renormalization-group framework and use it to construct higher-dimensional analogs of overscreened fixed points in arbitrary dimension $d\le 4$. We show that these models are governed by a nontrivial conformal fixed point and uncover a mechanism by which relevant perturbations destroy this criticality: symmetry-breaking masses generate nonperturbative corrections that drive the system away from the conformal point toward strong coupling, triggering dynamic mass generation. This provides a controlled pathway from a non-Fermi-liquid metal to a gapped phase with a rich order-parameter manifold.

A generic question in the field of ultrafast dynamics is concerned with the relaxation dynamics and the subsequent thermalization of optically excited charge carriers. Among several possible relaxation channels available in a solid-state system, we focus on the coupling to magnetic excitations. In this paper, we study the real-time dynamics of a paradigmatic model, the Kondo lattice model in one dimension. We conduct a comprehensive study of the relaxation processes by evaluating the spin polarization of the conduction electron, the local spin-spin correlation between localized and conduction electrons, and the electronic momentum distribution. While in the well-studied cases of one or two charge carriers in a ferromagnetic background, no thermalization occurs, we demonstrate that the stationary state is compatible with thermalization if either the electronic filling is finite or the magnetic background is in the singlet sector. Our real-time simulations using the time-dependent Lanczos method are corroborated by a direct comparison with finite-temperature expectation values and an analysis of the spectrum in terms of the gap ratio.

We analytically study the interaction between a single confined spin with a four-level $\mathrm{\Pi }$ configuration in an optical cavity and a single photon. The spin's ground and excited manifolds are each split into two levels coupled by circularly polarized optical transitions. Starting from the spin in an excited state, we analyze the spontaneous emission of the photon, which leaves the spin and photon entangled, and then follow the subsequent time evolution of the system under delayed feedback. We examine how photon reabsorption depends on energy splittings in both the ground and excited spin states, and how the feedback delay influences the degree of spin-photon entanglement. Finally, we identify the conditions that maximize this entanglement after photon reabsorption and re-emission.

The electric Hall effect (EHE) is a newly identified Hall effect characterized by a perpendicular electric field inducing a transverse charge current in two-dimensional (2D) systems. Here, we propose a spin and valley version of EHE in ballistic tunnel junctions. We demonstrate that the transverse spin and valley currents can be generated in an all-in-one tunnel junction based on a buckled 2D hexagonal material in response to a perpendicular electric field, referred to as the electric spin and valley tunneling Hall effects, respectively. These effects arise from the perpendicular-electric-field-induced backreflection phase of electrons in the junction spacer, independent of Berry curvature. The valley Hall conductance exhibits an odd response to the perpendicular electric field, whereas the spin Hall conductance shows an even one. The predicted effects can further enable the transverse separation of a pair of pure spin-valley-locked states with full spin-valley polarization while preserving time-reversal symmetry, as manifested by equal spin and valley Hall angles. Our findings present a mechanism for realizing the spin and valley Hall effects and provide a route to the full electric-field manipulation of spin and valley degrees of freedom, with significant potential for future applications in spintronics and valleytronics.

Growing research focuses on chiral quasibound states in the continuum (q-BICs) due to urgent needs in left-/right-circularly polarized (LCP/RCP) detection and absorption devices. Conventional chiral q-BICs suffer from quickly decaying quality factors (Q factors), making robust high-Q responses critical. Here, we present a planar chiral metasurface absorber with dynamically tunable chirality, enabled by a periodically arranged sixfold-symmetric double-skeleton-fan (DSF) structure and backed by a metallic mirror. Introducing gap perturbations folds guided modes above the light cone via Brillouin zone folding (BZF), creating robust high-Q BZF-BICs with topological singularities. Breaking in-plane ${\mathrm{C}}_2$ symmetry transforms BZF-BICs into high-Q q-BZF-BICs and generates a pair of C points, achieving strong extrinsic absorption circular dichroism (absorption $\mathrm{CD}=-0.96$, $Q>{10}^7$) and near-perfect RCP absorptance (0.997) verified by temporal coupled-mode theory. Breaking $z$ symmetry reveals a BZF-accidental BIC (BZF-A-BIC) on the guided resonance band, directly enabling high-Q intrinsic chiral absorptance (absorption $\mathrm{CD}=-0.87$, $Q>{10}^6$). Notably, we demonstrate dynamically tunable intrinsic chirality with sign reversal (absorption ${\mathrm{CD}}_{\text{max}}=0.91$ and tunable range ${\mathrm{\Delta }}_{\text{CD}}=1.78$) using phase-change material ${\mathrm{Sb}}_2{\mathrm{Se}}_3$, showcasing flexibility for chiral sensing, lasing, and imaging in future.

The non-Hermitian skin effect is a unique feature of non-Hermitian systems, in which an extensive number of boundary modes appear under open boundary conditions. It has been determined that this effect originates from intrinsic non-Hermitian topology protected by spatial symmetry or particle-hole symmetry. Here, we reveal another kind of skin effect which is protected by custodial chiral symmetry. Custodial chiral symmetry is common in the standard model of particle physics. Recent investigations have shown that such symmetry is also present in a classical Su-Schrieffer-Heeger electrical circuit with memory. We extend this discussion to non-Hermitian systems. It is shown that the skin effect can appear through the introduction of memristors that break the conventional chiral symmetry while giving rise to an emergent custodial chiral symmetry. This skin effect protected by custodial chiral symmetry, along with the associated topological edge states, enables tunable non-Hermitian topological behavior and exhibits strong robustness against perturbations.

The giant magnetoresistance with a huge hysteresis is observed in the organic metal $\kappa$-(BEDT-TTF)${}_2{\mathrm{Hg}\left(\mathrm{SCN}\right)}_2\mathrm{Br}$ at low temperature in a pressure interval around $3\mathrm{kbar}$ of a width $\sim 1\mathrm{kbar}$. The hysteretic magnetoresistance is isotropic with respect to the direction of magnetic field, which excludes the orbital effect of magnetic field as its origin. The observed temperature and magnetic-field dependence of this hysteresis and of its relaxation time indicates the strong influence of the spin-glass state on magnetoresistance. Although a quantitative theory of this effect, originating from strong electronic correlations, requires complex numerical calculations, we suggest its explanation and a simple model which qualitatively describes the observed magnetoresistance behavior and shows a strong charge-spin entanglement. The proposed effect suggests another class of extreme magnetoresistance mechanisms.

Characterizing bipolaron binding, and understanding how it depends on electron-phonon interaction, is crucial to unraveling the nature of emergent many-body states in strongly interacting electron-phonon systems. So far, most studies of bipolarons have been limited to the Holstein model, in which the coupling constant is momentum independent. The paradigmatic example of momentum-dependent electron-phonon interaction comes from the system in which phonon distortions modify electron hopping, the SSH model. Already individual polarons in the SSH model are richer than the Holstein model counterparts, and feature a phase transition into the finite momentum ground state with increasing electron-phonon interaction. In this paper, we use a variational approach to study bipolarons in the one-dimensional SSH model and discuss their ground-state, dispersion, and excitation spectra. We explore the full parameter range of the system, including the adiabatic regime of slow phonons, which was inaccessible to previous theoretical studies. In agreement with earlier studies, we find that in the anti-adiabatic strongly interacting regime, bipolarons have low effective mass. By contrast, in the adiabatic regime, we find that increasing electron-phonon interactions results in an exponential increase of the bipolaron mass. We establish the existence of multiple branches of bound excited states of SSH bipolaron and discuss the signatures of these bound states in dynamics. We show that in the anti-adiabatic regime, response functions obey a parity selection rule that imposes symmetry constraints on the excitation spectra and provides a clear signature of SSH bipolarons.

Building on the infinite-component Chern–Simons theory of three-dimensional fracton phases by Ma et al. [Phys. Rev. B 105, 195124 (2022)] and the Toeplitz braiding of anyons by Li et al. [Phys. Rev. B 110, 205108 (2024)], we show that stacking $(3+1)\mathrm{D} BF$ topological field theories, which serve as low-energy effective descriptions of a class of three-dimensional topological orders, along a fourth spatial direction gives rise to an exotic class of four-dimensional fracton phases. Their low-energy physics is governed by a new field-theoretic framework, namely infinite-component $BF$ ($\mathrm{i}BF$) theories, characterized by asymmetric integer Toeplitz $K$ matrices. Under open boundary conditions along the stacking direction, $\mathrm{i}BF$ theories with properly chosen $K$ matrices exhibit a striking phenomenon termed Toeplitz particle–loop braiding, where a particle and a loop placed on opposite three-dimensional boundaries acquire a strongly oscillating yet robustly nonvanishing braiding phase even at infinite separation. This nonlocal braiding admits a geometric interpretation: adiabatically transporting the particle induces a winding boundary trajectory on the opposite boundary that encircles the loop. We show that this robustness originates from boundary zero singular modes (ZSMs) of Toeplitz $K$ matrices revealed by singular value decomposition, rather than from boundary zero eigenmodes responsible for previously known Toeplitz braiding of anyons, and that the same ZSM mechanism also underlies directional amplification in the rapidly developing field of non-Hermitian physics. We analytically and numerically study representative $\mathrm{i}BF$ theories with Hatano–Nelson–type and non-Hermitian Su–Schrieffer–Heeger–type $K$ matrices, establishing a universal correspondence between ZSMs and Toeplitz particle–loop braiding. Our results identify boundary zero singular modes as the operative mechanism behind Toeplitz particle–loop braiding and establish infinite-component $BF$ theory as a predictive framework for higher-dimensional fracton topological orders.

We propose a bilayer Kane-Mele-Haldane model that realizes spin-selective higher-order topology and generates spin-polarized corner states without the need for external magnetic fields. A single layer combining intrinsic spin-orbit coupling, a Haldane mass, and a staggered sublattice potential supports a spin-selective quantum anomalous Hall phase, in which only one spin sector carries a nontrivial Chern number. When two layers with distinct parameters are coupled, the bilayer system enters a higher-order topological insulating phase hosting robust spin-polarized corner modes. These corner states are characterized by nonzero spin-resolved winding numbers protected by mirror symmetry, and edge analysis reveals that they originate from Dirac mass domain walls. Furthermore, to provide a spatial-symmetry-independent characterization, we introduce spin-resolved entanglement topological invariants, which independently diagnose the number of protected corner modes in each spin channel. Our results establish a spin-selective extension of the bilayer coupling mechanism, offering a controlled route to engineer spin-resolved higher-order topological states.

We study the boundary criticality in 2D interacting topological insulators. Using the determinant quantum Monte Carlo method, we present a nonperturbative study of the boundary quantum phase diagram in the Kane-Mele-Hubbard-Rashba model. Our results reveal rich boundary critical phenomena at the quantum phase transition between a topological insulator and an antiferromagnetic insulator, encompassing ordinary, special, and extraordinary transitions. Combining analytical derivation of the boundary theory with unbiased numerically exact quantum Monte Carlo simulations, we demonstrate that the presence of topological edge states enriches the ordinary transition that renders a continuous boundary scaling dimension and, more intriguingly, leads to a special transition of the Berezinskii-Kosterlitz-Thouless type. Our work establishes a framework for the nonperturbative study of boundary criticality in two-dimensional topological systems with strong electron correlations.

We report direct spectroscopic measurements of the dynamic effective mass in high‐mobility GaAs/AlGaAs two‐dimensional electron systems (2DESs) via disk‐geometry plasma resonances. From the zero‐field plasmon frequency and independently measured electron density, we extract the dynamic quasiparticle effective mass using the standard two-dimensional plasmon relation. It is established that with decreasing electron density (increasing parameter $r_s$ up to 4) the effective mass of electrons increases by 37% compared to the cyclotron electron mass. The comparison to previous experimental works proves that observed phenomenon can be ascribed to the renormalization of the Fermi-liquid quasiparticle mass at the Fermi surface. Our results demonstrate that collective‐mode spectroscopy provides a direct and complementary method to study many-body effects in 2DESs.