Thouless pumping, not only achieving quantized transport but also immune to moderate disorder, has attracted growing attention in both experiments and theories. Here, we explore how particle-particle interactions affect topological transport in a periodically modulated and tilted optical lattice. Three characterized interaction effects are revealed: topological pumping of bound states, interaction blockade of scattering states, and topologically resonant tunnelings. Attributed to the tilting, we have found a linear scanning in the first Brillouin zone at each Bloch-oscillation period of multiparticle center-of-mass momentum. Not limited to multiparticle Wannier states, our scheme ensures a dispersionless quantized transport even for initial Gaussian-like wave packets of interacting bosons which do not uniformly occupy a given band. Our study deepens the understanding of correlation effects on topological states, and provides a feasible way for detecting topological properties in interacting systems.

We study magnetism in the $\kappa$-(${\mathrm{ET})}_{2}X$ family of charge-transfer salts using implanted muon spectroscopy in conjunction with detailed ab initio electronic structure calculations using density functional theory (DFT). ET stands for the electron donor molecule bis(ethylendithio)tetrathiafulvalene and $X$ is an anion. The DFT calculations are used to establish molecular spin distributions, muon stopping sites, and dipolar field parameters, that allow us to make a quantitative interpretation of the experimental results. Materials in the $\kappa$-(${\mathrm{ET})}_{2}X$ family with $X$ = ${\mathrm{Ag}}_2{\left(\mathrm{CN}\right)}_3$ and $X$ = ${\mathrm{Cu}}_2{\left(\mathrm{CN}\right)}_3$ have attracted particular interest, as they have the attributes of quantum spin liquids, showing no magnetic ordering down to 30 mK in zero field $\mu \mathrm{SR}$ and in NMR, despite having exchange couplings of order 200–250 K. In contrast, the material with $X$ = $\mathrm{Cu}\left[\mathrm{N}{\left(\mathrm{CN}\right)}_2\right]\mathrm{Cl}$ has an antiferromagnetic (AF) ordering transition with $T_{\mathrm{N}}$ in the region of 23–30 K. In order to better understand the muon spectroscopy signature of magnetism in this whole family of compounds at both low and high magnetic fields, we look in detail at the case $X$ = $\mathrm{Cu}\left[\mathrm{N}{\left(\mathrm{CN}\right)}_2\right]\mathrm{Cl}$. As the first step in our study, the spin density distribution for the ET dimer is calculated using DFT and used to simulate the 3.7 T ${}^1\mathrm{H}$-NMR spectrum of this salt, with the spectrum showing good agreement with that measured previously [K. Miyagawa, A. Kawamoto, Y. Nakazawa, and K. Kanoda, Phys. Rev. Lett. 75, 1174 (1995)]. Best match to the data is found for antiferromagnetic interlayer ordering and an ordered moment per dimer of $0.25{\mu }_{\mathrm{B}}$. DFT is also used to explore muon stopping sites for this salt, finding one set of sites resulting from muonium addition to C=C double bonds in the ET layer, with muons stopping in the anion layer forming another group of sites. The dipolar fields associated with each of the stopping sites is computed and these are compared with the precession frequencies observed in the ZF-$\mu \mathrm{SR}$ spectrum [M. Ito, T. Uehara, H. Taniguchi, K. Satoh, Y. Ishii, and I. Watanabe, J. Phys. Soc. Jpn. 84, 053703 (2015)]. Best match to the ZF-$\mu \mathrm{SR}$ spectrum is obtained with the mode of interlayer ordering having FM character and an ordered moment per dimer of $0.31{\mu }_{\mathrm{B}}$ for muon sites in the anion layer and $0.36{\mu }_{\mathrm{B}}$ for muonium sites in the ET layer. New measurements of TF-$\mu \mathrm{SR}$ spectra for fields up to 8 T are reported and analyzed to obtain the best estimate of the magnetic order parameter under different measurement conditions, allowing us to observe the variation of $T_{\mathrm{N}}$ with applied field and the field-induced transverse canting of the moments.

We propose and experimentally demonstrate a method to strongly increase the sensitivity of spin measurements on nitrogen vacancy (NV) centers in diamond, which can be readily implemented in existing quantum sensing experiments. While charge state transitions of this defect are generally considered a parasitic effect to be avoided, we show here that these can be used to significantly increase the NV center's spin contrast, a key quantity for high-sensitivity magnetometry and high-fidelity state readout. The protocol consists of a two-step procedure, in which the charge state of the defect is first purified by a strong laser pulse, followed by weak illumination to obtain high spin polarization. We observe a relative improvement of the readout contrast by $17\%$ and infer a reduction of the initialization error of more than 50%. The contrast enhancement is accompanied by a beneficial increase of the readout signal. For long sequence durations, typically encountered in high-resolution magnetometry, a measurement speedup by a factor of $>1.5$ is extracted, and we find that the technique is beneficial for sequences of any duration. Additionally, our findings give detailed insight into the charge and spin polarization dynamics of the NV center and provide actionable insights for direct optical, spin-to-charge, and electrical readout of solid-state spin centers.

We predict superconductivity for the carbon–boron clathrate ${\mathrm{SrB}}_3{\mathrm{C}}_3$ with $T_c=27\text{–}43\mathrm{K}$ for Coulomb pseudopotential (${\text{μ}}^{*}$) values between 0.17 and 0.10 using first-principles calculations with conventional electron–phonon coupling. Electrical transport measurements, facilitated by an in situ experimental design compatible with extreme synthesis conditions ($>3000\mathrm{K}$ at 50 GPa), show nonhysteretic resistivity drops that track the calculated magnitude and pressure dependence of superconductivity for ${\text{μ}}^{*}\approx 0.15$, and transport measurements collected under applied magnetic fields indicate superconductivity with an onset $T_c$ of approximately 20 K at 40 GPa. Carbon-based clathrates thus represent a class of superconductors similar to other covalent metals like ${\mathrm{MgB}}_2$ and doped fullerenes. Carbon clathrates share structures similar to superconducting superhydrides with wide potential for tunable properties, and covalent C–B bonds allow metastable persistence at ambient conditions.

The supersolid phase characterized by the superfluid and long-range spatial periodicity of crystalline order is central to many branches of science ranging from condensed matter physics to ultracold atomic physics. Here we study a self-ordered checkerboard supersolid phase originating from dynamical spin-orbit coupling for a transversely pumped atomic Bose-Einstein condensate trapped in a ring cavity, corresponding to a superradiant anti-Tavis-Cummings phase transition. In particular, an undamped gapless Goldstone mode is observed in contrast to the experimentally realized lattice supersolid with a gapped roton mode for Dicke superradiance. This zero-energy mode reveals the rigidity of the self-ordered superradiant phase, which spontaneously breaks a continuous translational symmetry. Our work will highlight the significant opportunities for exploring long-lived supersolid matter by utilizing dynamical spin-orbit coupling in controllable optical cavities.

The bulk photovoltaic (BPV) effect, a second-order nonlinear process that generates static current under light irradiation, requires centrosymmetric broken systems as its application platform. To realize measurable BPV photocurrent in spatially centrosymmetric materials, various schemes such as chemical doping, structural deformation, or electric bias have been developed. In this paper, we suggest that the magnetic proximity effect via van der Waals (vdW) interfacial interaction, a contact-free strategy, also breaks the centrosymmetry and generates large BPV currents. Using the ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ quintuple layer as an exemplary material, we show that magnetic proximity effect from $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ septuple layers yields a finite and tunable shift and injection photocurrents. We apply group theory and first-principles calculations to evaluate the layer-specific shift and injection current generations under linearly polarized light irradiation. We find that the magnetic injection photoconductivity that localized on the ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ layer can reach $>70\times {10}^8\mathrm{A}/\left({\mathrm{V}}^2\mathrm{s}\right)$, so that a one-dimensional linear current density on the order of 0.1 mA/nm can be achieved under an intermediate intensity light. In addition to charge current, we also extend our discussions into spin BPV current, giving pure photogenerated spin current. The vertical propagation direction between the charge and spin photocurrents suggests that they can be used individually in a single material. Compared with previously reported methods, the magnetic proximity effect via vdW interface does not significantly alter the intrinsic feature of the centrosymmetric material (e.g., ${\mathrm{Bi}}_2{\mathrm{Te}}_3$), and its manipulation can be easily achieved by the proximate magnetic configurations (of $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$), interlayer distance, and light polarization.

We investigate the nature of the quantum phase transition out of density-wave phase in a spinless fermion model with nearest- and next-nearest-neighbor interaction at one-third filling. Using extensive density matrix renormalization group (DMRG) simulations, we show that the transition changes it nature. For weak next-nearest-neighbor coupling the transition is of Kosterlitz-Thouless type, in agreement with bosonisation predictions. For large next-nearest-neighbor repulsion we provide numerical evidences that the transition belongs to the Pokrovsky-Talapov univerality class describing a nonconformal commensurate-incommensurate transition. We argue that the change of the nature of the transition is a result of incommensurability induced by frustration and realized even at zero doping. The implications in the context of the $XXZ$ chain with next-nearest-neighbor Ising interaction is briefly discussed.

Moiré patterns made of two-dimensional (2D) materials represent highly tunable electronic Hamiltonians, allowing a wide range of quantum phases to emerge in a single material. Current modeling techniques for moiré electrons require significant technical work specific to each material, impeding large-scale searches for useful moiré materials. In order to address this difficulty, we have developed a material-agnostic machine learning approach and test it here on prototypical one-dimensional (1D) moiré tight-binding models. We utilize the stacking dependence of the local density of states (SD-LDOS) to convert information about electronic band structure into physically relevant images. We then train a neural network that successfully predicts moiré electronic structure from the easily computed SD-LDOS of aligned bilayers. This network can satisfactorily predict moiré electronic structures, even for materials that are not included in its training data.

In isolated Hermitian systems, the bulk-boundary correspondence is generally thought of as a compelling principle guiding the occurrence of robust edge states through the topological invariants of the bulk. However, in open non-Hermitian systems that support non-Hermitian skin effects, the universality of the bulk-boundary correspondence has so far remained disputable in spite of being subjected to intensive studies. Here we provide analytical and numerical evidence of bulk-boundary correspondences for both skin and edge modes in 1D two-band non-Hermitian systems within the framework of a prototypical non-Hermitian Su-Schrieffer-Heeger model. Two different topological winding numbers, one on a Brillouin zone and the other on a generalized Brillouin zone, are defined to fully characterize the topological phases of matter and to understand such deterministic correspondences. In addition to the exact solutions for bulk states, we also obtain explicit solution forms for edge modes along with analytical conditions for their existence and localization, all exhibiting remarkable agreement with numerical results. Our results solve the elusive non-Hermitian topology and may facilitate experimental investigations of bulk-boundary correspondence in a wide range of non-Hermitian systems.

The persistent spin helix (PSH) is the stable spin state protected by SU(2) spin-rotation symmetry. Long-lived spin textures, referred to as helical and homogeneous spin modes, emerge as a result of this symmetry. These textures are potential candidates for the development of quantum and topological phenomena as well as information carriers in semiconductors. To this end, revealing the lifetime of all spin modes is of great importance. We experimentally reveal the lifetime of both helical and homogeneous spin modes in the vicinity of the PSH state by fully electrical means through quantum corrections to the conductivity. In a (001)-grown GaAs/AlGaAs two-dimensional electron gas, we measure the weak antilocalization in the condition where Rashba and Dresselhaus spin-orbit (SO) interactions coexist. According to the latest theory on magnetoconductance [Kammermeier et al., Phys. Rev. B 104, 235430 (2021)], the Cooperon triplet mode in the quantum corrections can be decoupled into helical and homogeneous spin modes in the vicinity of the PSH state, which allows each mode lifetime to be determined from the quantum interference effect. By using a real-space simulation in tandem with the experiment, we were able to simultaneously evaluate the relaxation rates of the two spin modes. Our results show that the ratio of Rashba and Dresselhaus SO coefficients is modulated by the top gate and that this quadratically changes the relaxation rates of the helical and homogeneous spin modes, which is consistent with theoretical predictions. These findings pave the way for exploring electron spin textures in various bandgap materials from semiconductors to metals.

Machine learning is emerging as a technology that can enhance physics experiment execution and data analysis. Here, we apply machine learning to accelerate the production of a Bose-Einstein condensate (BEC) of ${}^{87}\mathrm{Rb}$ atoms by Bayesian optimization of up to 55 control parameters. This approach enables us to prepare BECs of $2.8\times {10}^3$ optically trapped ${}^{87}\mathrm{Rb}$ atoms from a room-temperature gas in 575 ms. The algorithm achieves the fast BEC preparation by applying highly efficient Raman cooling to near quantum degeneracy, followed by a brief final evaporation. We anticipate that many other physics experiments with complex nonlinear system dynamics can be significantly enhanced by a similar machine-learning approach.

The possibility of electrically exciting and detecting magnon currents in magnetic insulators has opened exciting perspectives for transporting spin information in electronic devices. However, the role of the magnetic field and the nonlocal thermal gradients on the magnon transport remain unclear. Here, by performing nonlocal harmonic voltage measurements, we investigate magnon transport in perpendicularly magnetized ultrathin ${\mathrm{Tm}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (TmIG) films coupled to Pt electrodes. We show that the first harmonic nonlocal voltage captures spin-driven magnon transport in TmIG, as expected, and the second harmonic is dominated by thermoelectric voltages driven by current-induced thermal gradients at the detector. The magnon diffusion length in TmIG is found to be ${\lambda }_{\mathrm{m}}\sim 0.3\mu \mathrm{m}$ at 0.5 T and gradually decays to ${\lambda }_{\mathrm{m}}\sim 0.2\mu \mathrm{m}$ at 0.8 T, which we attribute to the suppression of the magnon relaxation time due to the increase of the Gilbert damping with field. By performing current-, magnetic field-, and distance-dependent nonlocal and local measurements we demonstrate that the second harmonic nonlocal voltage exhibits five thermoelectric contributions, which originate from the nonlocal spin Seebeck effect and the ordinary, planar, spin, and anomalous Nernst effects. Our work provides a guide on how to disentangle magnon signals from diverse thermoelectric voltages of spin and magnetic origin in nonlocal magnon devices, and establish the scaling laws of the thermoelectric voltages in metal/insulator bilayers.

Non-Hermitian degeneracies are classified as defective exceptional points (EPs) and nondefective degeneracies. While in defective EPs, both eigenvalues and eigenvectors coalesce, nondefective degeneracies are characterized merely by the emergence of degenerate eigenvalues. It is also known that all degeneracies are either symmetryprotected or accidental. In this paper, I prove that antiunitary symmetries protect all nondefective twofold degeneracies. By developing a 2D non-Hermitian tight-binding model, I have demonstrated that these symmetries comprise various symmetry operations, such as discrete or spatial point-group symmetries and Wick's rotation in the non-Hermitian parameter space. Introducing these composite symmetries, I present the protection of nondefective degeneracies in various parameter regimes of my model. This work paves the way to stabilizing nondefective degeneracies and offers a new perspective on understanding non-Hermitian band crossings.

We theoretically study the electronic structure of interface states in twisted stacks of three-dimensional topological insulators. When the center of the surface Dirac cone is located at a midpoint of a side of the Brillouin zone boundary, we find that an array of nearly independent one-dimensional channels is formed by the interface hybridization of the surface states, even when the moiré pattern itself is isotropic. The two counterpropagating channels have opposite spin polarization, and they are robust against scattering by spin-independent impurities. The coupling between the parallel channels can be tuned by the twist angle. The unique one-dimensional states can be understood as effective Landau levels where the twist angle works as a fictitious magnetic field.

The statistics of the fluctuations of quantum many-body systems are highly revealing of their nature. In driven-dissipative systems displaying macroscopic quantum coherence, as exciton polariton condensates under incoherent pumping, the phase dynamics can be mapped to the stochastic Kardar-Parisi-Zhang (KPZ) equation. However, it was argued theoretically that in two dimensions the KPZ regime may be hindered by the presence of vortices, and a nonequilibrium Berezinskii-Kosterlitz-Thouless behavior was reported close to the condensation threshold. We demonstrate here that, when a discretized two-dimensional (2D) polariton system is considered, universal KPZ properties can emerge. We support our analysis by extensive numerical simulations of the discrete stochastic generalized Gross-Pitaevskii equation. We show that the first-order correlation function of the condensate exhibits stretched exponential behaviors in space and time with critical exponents characteristic of the 2D KPZ universality class and find that the related scaling function accurately matches the KPZ theoretical one, stemming from functional renormalization group. We also obtain the distribution of the phase fluctuations and find that it is non-Gaussian, as expected for a KPZ stochastic process.

Fractional statistics of quasiparticle excitations often plays an important role in the detection and characterization of topological systems. In this paper, we investigate the case of a three-dimensional (3D) ${\mathbb{Z}}_2$ gauge theory, where the excitations take the form of bosonic spinon quasiparticle and vison flux tubes, with mutual semionic statistics. We focus on an experimentally relevant intermediate temperature regime, where sparse spinons hop coherently on a dense quasistatic and stochastic vison background. The effective Hamiltonian reduces to a random-sign bimodal tight-binding model, where both the particles and the disorder are borne out of the same underlying quantum spin liquid (QSL) degrees of freedom, and the coupling between the two is purely driven by the mutual fractional statistics. We study the localization properties and observe a mobility edge located close to the band edge, whose transition belongs to the 3D Anderson model universality class. Spinons allowed to propagate through the quasistatic vison background appear to display quantum diffusive behavior. When the visons are allowed to relax, in response to the presence of spinons in equilibrium, we observe the formation of vison depletion regions slave to the support of the spinon wave function. We discuss how this behavior can give rise to measurable effects in the relaxation, response, and transport properties of the system and how these may be used as signatures of the mutual semionic statistics and as precursors of the QSL phase arising in the system at lower temperatures.

Calculations combining first-principles electron-phonon ($e$-ph) interactions with the Boltzmann equation enable studies of ultrafast carrier and phonon dynamics. However, in materials with weak Coulomb screening, electrons and holes form bound excitons so their scattering processes become correlated, posing additional challenges for modeling nonequilibrium physics. Here we show calculations of ultrafast exciton dynamics and related time-domain spectroscopies using ab initio exciton-phonon (ex-ph) interactions together with an excitonic Boltzmann equation. Starting from the nonequilibrium exciton populations, we develop simulations of time-domain absorption and photoemission spectra that take into account electron-hole correlations. We use this method to study monolayer ${\mathrm{WSe}}_2$, where our calculations predict subpicosecond timescales for exciton relaxation and valley depolarization and reveal the key role of intermediate dark excitons. The approach introduced in this paper enables a quantitative description of nonequilibrium dynamics and ultrafast spectroscopies in materials with strongly bound excitons.