In this work, we show that the unique bulk-edge correspondence can serve as a fingerprint for identifying topological excitonic insulators, with the $\mathrm{LiFe}X$ ($X=\mathrm{S}$, Se, and Te) family as a prototype. First-principles Bethe-Salpeter equation calculations reveal excitonic instabilities in these spin-orbit coupling quantum anomalous Hall insulators. Effective Hamiltonian analyses indicate that spontaneous exciton condensation does not disrupt the gapless edge state but reconstructs the bulk gap to be almost independent of the spin-orbit coupling strength. This change in the bulk-edge correspondence can be experimentally inspected by angle-resolved photoemission spectroscopy or electron compressibility measurements, providing observational evidence for the identification of topological excitonic insulators.

We use a simple one-dimensional two-band model with electron-phonon coupling to illustrate some of the complications that arise in multiband systems when trying to extract a self-energy using the typical approach used for single-band systems when analyzing angle-resolved photoemission spectroscopy (ARPES) data. The underlying reason is that in multiband models, the self-energy is a matrix, not a scalar, and the result obtained from the ARPES analysis is a complicated function of all these self-energy matrix elements, weighted by different dipole matrix elements of the relevant Wannier orbitals. We contrast the results for Holstein and Peierls electron-phonon couplings to further illustrate differences between models with a local versus nonlocal self-energy matrix.

Across most qubit platforms, the readout fidelities do not keep up with the gate fidelities, and new ways to increase the readout fidelities are searched for. For semiconductor spin qubits, a typical qubit-readout signal consists of a finite stretch of a digitized charge-sensor output. Such a signal trace is usually analyzed by compressing it into a single value, either maximum or sum. The binary measurement result follows by comparing the single value to a decision threshold fixed in advance. This threshold method, while simple and fast, omits information that could potentially improve the readout fidelity. Here, we analyze what can be achieved by more sophisticated signal-trace processing using the hidden Markov model (HMM). The HMM is a natural choice, being the optimal statistical processing if the noise is white. It also has a computationally efficient implementation, known as the forward-backward algorithm, making HMM processing practical. However, unlike in many computer-simulation studies, in real experiments the noise is correlated. How this change affects the HMM implementation and reliability is our subject. We find that the HMM using white noise as the system statistical model is surprisingly sensitive to correlations; it only tolerates very small correlation times. We suggest alleviating this deficiency by a signal prefiltering. The correlations have a similar strongly negative impact on the HMM model calibration (the Baum-Welch algorithm). Besides studying the effects of noise correlations, as a specific application of the HMM we calculate the readout fidelity at elevated temperatures, relevant to recent experimental pursuits of hot spin qubits.

Dark solitons carrying quantized phase information have inspired great interest in different nonlinear systems. A dark soliton in one dimension can be stabilized in microcavity polariton condensates as a confinement is imposed on it to prevent its decay. Such a confinement can be realized by optical methods, i.e., by using optically induced potential traps. Under nonresonant excitation with spatially periodically modulated optical beams, we numerically demonstrate that, besides fundamental dark solitons, higher-order dark solitons with multiple density minima and $\pi$-phase jumps can also stably survive in the potential (pump) valleys. Simultaneously exciting several orders of dark soliton states by properly choosing the lattice constant of the optical pump gives rise to dark oscillators. In some cases, the stably trapped dark solitons in adjacent pump valleys squeeze the condensate density between them and generate another type of density dip in the pump peak area. Surprisingly, such a density dip supports another stable dark soliton with a larger size that is essentially composed of two dark solitons, and the two $\pi$-phase jumps enable efficient optical control of dark solitons.

We evaluate the transport gaps in the most prominent fractional quantum Hall states in the $n=0$ and $n=1$ Landau levels of graphene, accounting for the Coulomb interaction, lattice-scale anisotropies, and one-body terms. We find that the fractional phases in the $n=0$ Landau level are bond ordered, while those in the $n=1$ Landau level are spin-valley entangled. This resolves a long-standing experimental puzzle [F. Amet et al., Nat. Commun. 6, 5838 (2015)] of the contrasting Zeeman dependence of the transport gaps in the two Landau levels. The spin-valley entangled phases host gapless Goldstone modes that can be probed via bulk thermal transport measurements. As a byproduct of our computations, we place strong constraints on the values of the microscopic anisotropic couplings such that these are consistent with all known experimental results.

We study magnetotransport through topological insulator nanowires shaped in the form of a constriction, as can be obtained by etching techniques. The magnetic field is coaxial turning the nanowire into a magnetochiral junction. We show in a detailed analytical and numerical study that two main transport regimes emerge, depending on the central narrow region being short or long as compared to the magnetic length at the junction entrance and exit. In both cases the central region hosts Dirac-particle-in-a-box states due to magnetic confinement, whose conductance properties are strongly influenced by Landau levels at the ends of the constriction. Notably, in the low-energy regime only chiral states with a specific handedness can transport charge across the junction. Based on these properties and general symmetry considerations we argue that the shaped nanowire should exhibit strong magnetochiral nonreciprocal transport beyond linear response. We employ a numerical tight-binding implementation of an effective 2D model on a nonhomogeneous grid, capable of simulating samples of realistic sizes, and test its soundness against full simulations for scaled-down 3D topological insulator wires.

Two-dimensional (2D) Janus materials show great promise as piezoelectric materials and photocatalysts for water splitting. In this work, we systematically investigated the piezoelectric and photocatalytic properties of the hexagonal Janus $\mathrm{In}XY$ ($X=\mathrm{S}$, Se, Te; $Y=\mathrm{Cl}$, Br, I) monolayers (MLs) using first-principles calculations. Except for InSeCl ML, the remaining eight $\mathrm{In}XY$ MLs are stable and exhibit exceptionally high in-plane piezoelectric coefficients ($|d_{22}|=6.07–155.27\mathrm{pm}/\mathrm{V}$), which exceed those of most known 2D materials. $\mathrm{In}XY$ MLs possess band edges straddling the water redox potentials at pH = 0. Their intrinsic vertical polarization induces an intralayer polarization field $E_{\mathrm{intra}}$, leading to low exciton binding energies (0.44–0.78 eV). Moreover, their strong vertical piezoelectric responses ($|d_{32}|=0.34–0.65\mathrm{pm}/\mathrm{V}$) suggest that in-plane stress can further enhance $E_{\mathrm{intra}}$ and facilitate the separation of photogenerated carriers. Additionally, these $\mathrm{In}XY$ MLs exhibit high electron mobility ($101–899{\mathrm{cm}}^2/\mathrm{V}/\mathrm{s}$) and a pronounced anisotropy ratio in carrier mobility, which effectively suppresses charge recombination. Among them, several stand out: InSI and InSeBr MLs show high electron mobility and a large carrier mobility anisotropy ratio; InSeBr ML exhibits excellent in-plane and out-of-plane piezoelectricity; and InSeBr, InSeI, and $\mathrm{InTe}Y$ ($Y=\mathrm{Cl}$, Br, I) MLs show strong visible light absorption. To optimize performance, we constructed a van der Waals heterojunction (InSI/InSeBr), which demonstrates remarkable photocatalytic properties, including enhanced redox ability, a direct Z-scheme charge transfer pathway, strong visible light absorption, high carrier mobility, and excellent photocorrosion resistance. Our results indicate that hexagonal Janus $\mathrm{In}XY$ MLs and their heterojunctions are multifunctional materials integrating piezoelectricity and photocatalysis, paving the way for energy conversion applications.

Using the relativistic symmetrized linearized augmented cylindrical waves method, we investigated the electronic and spin states and transport properties in three series of the chiral single-walled GaAs nanotubes $\left(n_1,n_2\right)$ with $n_1=5$, 7, 10 and integer $0\le n_2\le n_1$. Except for opposite spin orientation in the right- and left-handed tubules, their electronic structures are independent on helicities. The qualitative assessments of spin conductivity and selectivity are obtained under the assumption that the electrons of boundary spin states located at the edges of valence and conduction bands take part in the spin transfer and that the probability of electron tunneling is higher with parallel orientation of the electron spin and chirality vectors of material compared to the case of their antiparallel orientation. The nanotubes most promising for the creation of spin currents and filters and their applications in spintronics are predicted.

We study the $k=3$ Read-Rezayi quantum Hall state by means of a purely bosonic matrix product state formulation, as described in detail. We calculate the density profiles in the presence of bulk quasiholes of six different types: one for each ${\mathbb{Z}}_3$ parafermion sector. From the density profiles, we calculate the (local) spins of these quasiholes. By employing a spin-statistics relation, we obtain the exchange statistics parameters. Our results, which are entirely based on local properties of the quasiholes, corroborate previous results obtained by explicitly braiding quasiholes, showing that the exchange statistics can be read off from the monodromy properties of the wave functions, i.e., the associated Berry phase vanishes. We also discuss the entanglement spectrum, to show that our bosonic matrix product state formulation correctly captures the ${\mathbb{Z}}_3$ parafermionic structure of the $k=3$ Read-Rezayi states.

In this work we perform ultrafast time-resolved reflectivity measurements to study the symmetry breaking in the charge-density wave (CDW) phase of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$. By extracting the coherent phonon spectrum in the CDW phase of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, we discover close phonon pairs near 1.3 THz and 3.1 THz, as well as a new mode at 1.84 THz. The 1.3 THz phonon pair and the 1.84 THz mode are observed up to the CDW transition temperature. Combining density-functional theory calculations, we show that these phonon pairs arise from the coexistence of Star of David and inverse Star of David distortions combined with sixfold rotational symmetry breaking. An anisotropy in the magnitude of transient reflectivity change is also revealed at the onset of CDW order. Our results thus indicate broken sixfold rotational symmetry in the charge-density wave state of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, along with the absence of nematic fluctuation above $T_{\text{CDW}}$. Meanwhile, the measured coherent phonon spectrum in the CDW phase of ${\mathrm{CsV}}_3{\mathrm{Sb}}_{5-x}{\mathrm{Sn}}_x$ with $x=0.03$–0.04 matches the staggered inverse Star of David with interlayer $\pi$ phase shift. This CDW structure contrasts with undoped ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ and explains the evolution from a phonon pair to a single mode at 1.3 THz by $x=0.03$–0.04 Sn doping.

We investigate both magnon and photon blockade for an antiferromagnetic insulator coupled to a linearly polarized cavity mode. We focus on the cross-Kerr nonlinearity between the two magnon modes, which can be large in antiferromagnets with a weak easy-axis magnetic anisotropy. By numerically solving the Lindblad master equations, we demonstrate that the resulting bright and dark modes, i.e., system eigenmodes that couple strongly and weakly to photons, respectively, exhibit distinct behaviors. The bright mode exhibits both magnon and photon blockade due to a weak effective nonlinearity, while the dark mode only exhibits magnon blockade for a detuned cavity photon. The blockade efficiency can further be optimized by appropriately tuning the competing interactions in the system. In addition, we show that applying a DC magnetic field, which lifts the degeneracy of antiferromagnetic chiral magnon eigenmodes, destroys the dark mode and leads to an unconventional photon blockade. These findings provide a pathway for generating single magnon and photon states useful for quantum information technology based on the underlying large squeezing of antiferromagnetic magnons.

We show that the Ruderman-Kittel-Kasua-Yoisida interaction between overscreened spins in two-channel Kondo impurity systems is a relevant perturbation when the number of impurities N is greater than 3 driving the system to a new quantum critical point with anomalous dimensions $\frac{1}{(N+1)}$ for the spin operator and the Sommerfeld coefficient of the specific heat scales as $\gamma \sim T^{-\frac{3}{N+1}}$. The critical point universal properties are relevant to many strong correlation problems, such as impurity placed in a Majorana metal and the multichannel Kondo lattice model of heavy fermion materials. We discuss relevance of our results for cluster DMFT studies of quantum criticality.

The one-dimensional (1D) $J_1\text{−}{J}_2$ $q$-state Potts model is solved exactly for arbitrary $q$ by analytically block-diagonalizing the original $q^2\times q^2$ transfer matrix into a simple $2\times 2$ maximally symmetric subspace, based on using OpenAI's reasoning model o3-mini-high to exactly solve the $q=3$ case. Furthermore, by matching relevant subspaces, we map the Potts model onto a simpler effective 1D $q$-state Potts model, where $J_2$ acts as the nearest-neighbor interaction and $J_1$ as an effective magnetic field, nontrivially generalizing a 56-year-old theorem previously limited to the simplest case ($q=2$, the Ising model). Our exact results provide insights to phenomena such as atomic or electronic order stacking in layered materials and the emergence of dome-shaped phases in complex phase diagrams. This work is anticipated to fuel both research in 1D frustrated magnets for recently discovered finite-temperature application potentials and the fast moving topic area of AI in science.

We theoretically investigate chiral domain walls (DWs) formed in radially magnetized nanotubes composed of ultrathin layers with perpendicular magnetic anisotropy (PMA). Unlike those with in-plane magnetic anisotropy, the stable configurations of DWs in PMA nanotubes are influenced not only by exchange interactions but also by magnetostatic interactions induced by the radial component of magnetization. Particularly, the magnetostatic interactions lead to Dzyaloshinskii-Moriya interaction (DMI)-like effects that stabilize chiral Néel-type DWs. We derive expressions for the effective magnetic fields acting on DWs within PMA nanotubes and quantify spin-orbit torque driven DW motion using an analytical one-dimensional model, which is validated by micromagnetic simulations. Our results show that the DMI-like field due to magnetostatic interactions can be as significant as the contribution of material-induced DMI in nanotubes with diameters below $100\mathrm{nm}$. This implies that the direction and speed of DW motion in the PMA nanotubes could differ from those observed in flat nanoribbons composed of the same material. Furthermore, we demonstrate that DW velocity can be effectively controlled by adjusting the tube diameter and exchange stiffness constant of the magnetic layer, rather than relying solely on material-induced DMI. These insights are expected to greatly expand the potential applications of PMA nanotube-based DW devices.

We study the localization transition in a class of nearest-neighbor quasiperiodic tight binding models in one dimension that has at least two separate periodic modulations. We show that these systems exhibit a reentrant localization transition where the periodicities of these modulations set the energy scale and the number of transitions. Furthermore, we show dynamical properties in these systems exhibit various kinds of critical dynamics, including the subdiffusive and superdiffusive spread of an initially localized wave packet in the thermodynamic limit due to the multifractal characteristics of the eigenstates. Finally, we show that these characteristics of quasiperiodic systems can be realized within the regime of current experiments.

A recently discovered phase of collinear magnets, called an altermagnet, breaks time-reversal symmetry (TRS) and exhibits momentum-dependent spin splitting of the band structure with zero net magnetization. In this work, we theoretically investigate the Josephson junction (JJ) of a spin singlet superconductor (SC)/altermagnet/spin triplet SC and demonstrate that it manifests the field-free Josephson diode effect (JDE). It has also been shown that by applying a gate potential in the altermagnetic regime, one can reverse the sign of efficiency and modulate its magnitude. For comparison we have also studied similar JJs with a ferromagnet as a barrier. Our analysis reveals that to realize the JDE with a TRS-broken barrier region one requires the presence of Rashba spin-orbit interaction, nonidentical superconductors, and either the barrier or one of the SCs should be unconventional with $d$-wave symmetry. Our system can be used as a superconducting rectifier that can be tuned efficiently using gate voltage and system parameters without having external magnetic field.