Non-Hermitian systems, going beyond conventional Hermitian systems, have brought in intriguing concepts such as exceptional points and complex spectral topology as well as exotic phenomena such as non-Hermitian skin effects. However, previous studies on non-Hermitian systems predominantly focused on the properties of eigenstates, with rather limited discussions on non-Hermitian dynamic phenomena. Motivated by going beyond the parity-time symmetry in non-Hermitian physics, here we theoretically study a one-dimensional non-Hermitian lattice with the glide-time symmetry. We reveal that the glide-time symmetry leads to unique spectral and topological properties and enables rich dynamic phenomena such as dynamic non-Hermitian skin effects with diverse behaviors. We classify different dynamic phases and show that the model enables remarkable tuning of the dynamics in the bulk as well as at the edge boundaries. These include the directional wave propagation and amplification in the bulk, as well as the wave trapping and the dynamic patterns at the edges. These properties do not appear in conventional non-Hermitian models such as the Hatano-Nelson model and nonreciprocal Su-Schrieffer-Heeger model. With these findings, our work serves as a steppingstone for future research on non-Hermitian topology and dynamics enriched by the lattice symmetry.

The discovery of Weyl and Dirac semimetals has produced a number of dramatic physical effects, including the chiral anomaly and Fermi arc surface states. A very different but no less dramatic physical effect is also to be found in these materials: discrete scale invariance. This invariance leads to quasibound-state spectra for Coulomb impurities that repeat when the binding energy is changed by a fixed factor, reminiscent of fractal behavior. We show that this effect follows from the peculiar dispersion relation in Weyl and Dirac semimetals. It is observed when such a material is placed in very strong magnetic field $B$: There are oscillations in the magnetoresistivity somewhat similar to Shubnikov–de Haas oscillations but with a periodicity in $lnB$ rather than $1/B$. These oscillations should be present in other thermodynamic and transport properties. The oscillations have now been seen in three topological semimetals: ${\mathrm{ZrTe}}_5$, ${\mathrm{HfTe}}_5$, and TaAs.

We have developed a method to construct a symmetry-adapted Wannier tight-binding model based on the closest Wannier formalism and the symmetry-adapted multipole theory. Since the symmetry properties of the closest Wannier functions are common to those of the original atomic orbitals, symmetry-adapted multipole basis (SAMB) can be defined as the complete orthonormal matrix basis set in the Hilbert space of the closest Wannier functions. Utilizing the completeness and orthonormality of SAMBs, the closest Wannier Hamiltonian can be expressed as a linear combination of the SAMBs belonging to the identity irreducible representation, thereby fully restoring the symmetry of the system. Moreover, the linear coefficients of each SAMB (model parameters) related to crystalline electric fields, spin-orbit coupling, and electron hoppings are determined through simple matrix projection without any iterative procedure. Thus, this method allows us to unveil mutual interplay among hidden electronic multipole degrees of freedom in the Hamiltonian and numerically evaluate them. We demonstrate the effectiveness of our method by modeling monolayer graphene under a perpendicular electric field, highlighting its utility in symmetrizing the closest Wannier model, quantifying symmetry breaking, and predicting unusual responses. The method is implemented in the open-source Python library SymClosestWannier, with the codes available on GitHub.

Neither hardcore bosons nor fermions can occupy the same lattice site-state. However, a nearest-neighbor interaction may counteract the hardcore effect, resulting in condensate states in a bosonic system. In this work, we unveil the underlying mechanism by developing a general method to construct the condensate eigenstates from those of sub-Hamiltonians. As an application, we find that a local on-site potential can induce an evanescent condensate mode. Based on this, exact condensate ground states of hardcore bosons, possessing off-diagonal long-range order, can be constructed when an array of impurities is applied. The effect of the off-resonance impurity on the condensate ground states is also investigated using numerical simulations of the dynamic response.

We report nonlinear transport in one-dimensional quantum wires formed in a GaAs/AlGaAs heterostructure. The two-terminal conductance characteristics were investigated under varying electron concentrations with and without a large in-plane magnetic field of 10 T. One important observation was that the 0.7-like feature was identified at higher-order subbands, specifically $\sim 1.6{\mathrm{G}}_0$, $\sim 3.7{\mathrm{G}}_0$, and $\sim 4.7{\mathrm{G}}_0$. Additionally, our findings reveal the emergence of two conductance states appearing below ${\mathrm{e}}^2/\mathrm{h}$ under large dc bias voltage, where these states become more pronounced together with higher 0.7-like features, as electron concentration decreases, highlighting the influence of strong correlation effects in their formation. The weak Zeeman splitting in the ground state despite a large in-plane magnetic field of 10 T in low-density and weakly confined regime indicates disordered-induced correlation effects dominating the mechanism.

α-phase ruthenium (III) chloride $\left(\alpha \text{−}{\mathrm{RuCl}}_3\right)$ has attracted significant attention because of its potential for realizing Kitaev quantum spin liquid. In this work, we employ first-principles many-body perturbation theory to study its many-electron interactions and excited-state properties. We find enhanced many-electron interactions that dominate quasiparticle (QP) energies and optical responses in $\alpha \text{−}{\mathrm{RuCl}}_3$. Our calculated QP band gap of the bulk structure is ∼1.75 eV, which agrees well with recent scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy measurements. Furthermore, our calculated first and second primary bright excitons are located at 1.23 and 1.98 eV, respectively. These excitons show good consistency with the main features observed in the optical absorption spectrum. We extend our investigation to monolayer $\alpha \text{−}{\mathrm{RuCl}}_3$, examining the zigzag antiferromagnetic (AFM) and ferromagnetic (FM) phases. In addition to the significant excitonic effect, the optical spectrum of the zigzag AFM phase exhibits anisotropic behavior, while the FM phase demonstrates isotropic characteristics. The different optical response behaviors provide an efficient approach to identify the nearly degenerate energy magnetic states, which can both potentially exist in fabricated samples.

Large-scale nonequilibrium molecular dynamics simulations of RDX shocked along [100] reveal a steady-state regime of elastic-plastic shock wave propagation along slip-hindered directions in molecular crystals. For a shock with a particle velocity of 1 km/s, steady state is achieved after approximately 100 ps or 0.5 microns from the impact plane. The transient regime is characterized by a dynamic evolution of plasticity, which transitions from the simultaneous nucleation of a high density of shear bands to the growth of fewer shear bands, each resulting in significant localized shear strain and temperature. This evolution of the plastic wave leads to a significant attenuation of the elastic precursor, with a 20% drop in stress along the shock direction. This significant variation in the structure of the shock wave over distances larger than most atomistic simulations to date highlights the need for continuing efforts toward scalable molecular simulations and the challenges in multiscale modeling of dynamical properties.

This study examines the spin-lattice relaxation rate of ${\mathrm{Mn}}^{2+}$ ions in strained diluted magnetic semiconductor (Cd,Mn)Te/(Cd,Mg)Te quantum wells using the optically detected magnetic resonance (ODMR) technique. By adjusting the magnesium (Mg) content in the buffer layer, we created samples with different strain levels. Our time-resolved ODMR results show that the spin-lattice relaxation time becomes faster as strain increases. We also found that the relaxation rate increases with both magnetic field and temperature, showing a power-law behavior. To understand these observations, we used a theoretical model based on six-level rate equations with nonequal level separations. This model suggests that the main factor affecting relaxation in our samples is a “direct” mechanism. The model's predictions match well with our experimental data. Overall, our findings give insights into spin-lattice relaxation in strained quantum wells and could be important for the development of future quantum and spintronic devices.

The introduction of optical chiral quasibound states in the continuum (QBICs) provides a promising perspective for manipulating light at the nanoscale. Their strong field enhancement together with their intrinsic low loss under dielectric conditions enable us to efficiently boost and control the chiral coupling. Recently, the large electric field localization and enhancement supported by the epsilon-near-zero (ENZ) modes have garnered significant attention for the realization of strong light-matter interactions. Here, we demonstrate an all-dielectric metasurface, which integrates a nanorod array lacking any point symmetry elements with an ultrathin ITO layer, achieving strong chiral QBIC-ENZ coupling with tunable coupling strength. A pronounced anticrossing behavior can be observed under specific circular polarization, revealing remarkable chiroptical characteristic hybridization. By employing the coupled oscillator model combined with near-field analysis, a Rabi splitting of up to 135.8 meV is confirmed. We also demonstrate that the coupling strength in the chiral hybrid system can be modulated by varying the ITO thickness, which shows an obvious increase with thickness and is accompanied by fine-tuned chiral responses of the hybrid polaritons. This work provides a paradigm for chiroptical coupling based on ENZ materials, which offers great potential for low-loss, high-compact chiral photonic devices and nonlinear applications.

Spinel superconductors offer an exciting platform to explore electron correlation, superconductivity, and geometric frustration, while their electronic structure has been barely resolved. Here, by combining high-quality thin-film growth, in situ angle-resolved photoelectron spectroscopy, and ultra-low-temperature scanning tunneling spectroscopy studies, we directly uncovered the electronic structure, electron correlation, and superconducting gap behavior in ${\mathrm{LiTi}}_2{\mathrm{O}}_4$ spinel superconductor. Anisotropic band renormalization and electron-phonon coupling (EPC) were observed, which are likely modulated by the saddle-point dispersion. The observed strong EPC and U-shaped superconducting gap demonstrate a Bardeen-Cooper-Schrieffer (BCS) framework in ${\mathrm{LiTi}}_2{\mathrm{O}}_4$, while there are likely pair-breaking effects related to the spin fluctuations and geometric frustration, which enriches the understanding of the interplay between electron correlations, geometric frustration, and EPC in spinel superconductors.

We present a new geometric characterization of generalized Landau levels (GLLs). The GLLs are a generalization of Landau levels to nonuniform Berry curvature, and are mathematically defined in terms of a holomorphic curve—an ideal Kähler band—and its associated unitary Frenet-Serret moving frame. Here, we find that GLLs are harmonic maps from the Brillouin zone to the complex projective space and they are critical points of the Dirichlet energy functional, as well as the static structure factor up to fourth order. We also find that filled GLLs exhibit quantized Hall viscosity, similar to the ordinary Landau levels. These results establish GLLs as a versatile generalization of Landau levels.

By scanning tunneling microscopy (STM) we have probed the local quasiparticle density of states (DOS) of the Bechgaard salt organic superconductor ${\left(\mathrm{TMTSF}\right)}_2{\mathrm{ClO}}_4\mathrm{in}$ slowly cooled single crystals cleaved under ultrahigh vacuum conditions. In well STM imaged crystallographic surface planes, the local DOS has been probed for different surface areas at temperatures above and below the critical temperature of superconducting or insulating spin density wave states. While a rather homogeneous superconducting state is expected in the bulk from previous studies, depending on the degree of disorder introduced by cleavage in the anion lattice, an inhomogeneous granular state is predominantly observed at the surface. A pronounced linear V-shape profile of the local DOS is observed from intermediate to the lowest-energy scale in the less disordered superconducting surface areas. This supports the existence of an unconventional $d$-wave-like order parameter with nodes at low energy, which is preceded by more energetic fluctuations attributed to quantum criticality of the material. At higher energy disorder combined to correlations deplete further the DOS. By contrast, a nonlinear U shape characterizes the local low-energy DOS profile for the more disordered and insulating surface areas of the spin density wave state. The experimental results are compared quantitatively with those predicted by the renormalization group theory of the quasi-one-dimensional electron gas model and its description of the superconducting and spin density wave states that are interlinked by quantum criticality in the Bechgaard salts.

While the high-temperature spin diffusion in spin chains with random local fields has been the subject of numerous studies concerning the phenomenon of many-body localization (MBL), the energy diffusion in the same models has been much less explored. We demonstrate that energy diffusion is faster at weak random fields but becomes essentially equal at strong fields; hence, both diffusions determine the slowest relaxation timescale (Thouless time) in the system. Numerically reachable finite-size systems reveal the anomalously large distribution of diffusion constants with respect to actual field configurations. Despite the exponential-like dependence of diffusion on field strength, the results for sensitivity to twisted boundary conditions are incompatible with the Thouless criterion for localization and the presumed transition to MBL, at least for numerically reachable sizes. In contrast, we find indications of the scenario of subdiffusive transport, particularly in the dynamical diffusivity response.

We study in depth the charge susceptibility for the band Hatsugai-Kohmoto and orbital models. As either of these models describes a Mott insulator, the charge susceptibility takes on the form of a modified density response function with lower and upper Hubbard bands, thereby giving rise to a multipole structure. The particle-hole continuum consists of hot spots along the $\omega$ vs $q$ axis arising from interband transitions. Such transitions, which are strongly suppressed in noninteracting systems, obtain here because of the nonrigidity of the Hubbard bands. This modified density response function gives rise to a plasmon dispersion that is inversely dependent on the momentum, resulting in an additional contribution to the conventional $f$-sum rule. This extra contribution originates from a long-range diamagnetic contribution to the current. This results in a noncommutativity of the long-wavelength ($q\to 0$) and thermodynamic ($L\to \infty$) limits. When the correct limits are taken, we find that the Kubo response computed with either open- or periodic boundary conditions yields identical results that are consistent with the continuity equation contrary to recent claims. We also show that the long-wavelength pathology of the current noted previously also plagues the Anderson impurity model interpretation of dynamical mean-field theory.

In systems with spin-momentum locking, such as the surface states of three-dimensional topological insulators, a charge current is spin-polarized and spin-flip interactions between electron and nuclear spins can transfer this polarization to the nuclear spin system. When a nonzero bias voltage is applied, the nuclear polarization reaches a steady-state value. This polarization emerges as an effective in-plane magnetic field acting on electrons, called the Overhauser field, which causes an offset in-plane magnetoresistance perpendicular to the current, visible in experiments. The in-plane offset is measured in the three-dimensional topological insulator ${\left({\mathrm{Bi}}_{1-x}{\mathrm{Sb}}_x\right)}_2{\mathrm{Te}}_3$, and the magnitude of the magnetic field offset is compared to the Overhauser field. We attribute the observed magnetic field offset to current-induced nuclear polarization in ${\left({\mathrm{Bi}}_{1-x}{\mathrm{Sb}}_x\right)}_2{\mathrm{Te}}_3$, which forms an important step towards experimentally realizing an entropic inductor.

Defects have a profound effect on the electronic and transport behavior of materials. They play an important role in many photoelectric devices. Here, we investigate by means of constrained density functional theory (C-DFT) the spatial distribution and transport properties of bipolarons that are induced by surface oxygen vacancies (${\mathrm{O}}_{\mathrm{v}}$) on reduced rutile $\mathrm{Ti}{\mathrm{O}}_2$ (110) surfaces. We find that bipolarons preferentially localize in a subsurface geometry, followed by a mixed surface-subsurface localization, while a surface state is the energetically least preferred location for bipolarons. We show that this unique behavior is caused by an interplay of the splitting of titanium $d$ orbitals, the orbital symmetry, and the electrostatic potential. Also, the polaron transport properties are examined, both parallel and perpendicular to the surface. The introduction of water molecules on the surface can effectively lead to the transfer of subsurface polarons to a position on the surface. The preferred transfer direction of polarons changes from the [001] direction to the [110] direction when the water coverage exceeds one-half monolayer. This characteristic behavior is strongly related to the synergetic effect of the electronic coupling strength and the transition barrier at different water coverages. Our findings reveal the energetic order of bipolaron localizations, their transport properties, and the effect of water on a reduced rutile $\mathrm{Ti}{\mathrm{O}}_2$ (110) surface, hence leading to a better understanding of the role of polarons in photoelectric applications.

We comprehensively investigate two-color-laser-driven photocurrent and high harmonic generation (HHG) in graphene models. By numerically solving the quantum master equation, we uniformly explore a broad parameter regime including both the weak (perturbative) and intense-laser (nonperturbative) cases while considering the dissipation effects. We demonstrate that the HHG spectra can be drastically altered by tuning the real-space path traced by the laser electric field. This controllability is explained by the dynamical symmetry argument. We also show that both the magnitude and the direction of photocurrent (zeroth order harmonics) can be controlled by varying the frequency, intensity, ellipticity, and relative phase of the two-color laser. Furthermore, the nature of photocurrent is shown to be classified into shift- or injection-current types, depending on the phase of two-color laser. Our findings indicate that even in centrosymmetric electron systems, photocurrent and HHG can be quantitatively controlled by adjusting various external parameters if we utilize multicolor laser with a lower spatial or temporal symmetry.

We report direct measurement of the dispersion relation of polaritons in GaAs/AlGaAs microcavity structures at room temperature, which clearly shows that the polaritons are in the strong-coupling limit. The Rabi splitting ranges from 12.3 to 15.2 meV depending on the detuning, significantly exceeding the heavy-hole exciton half width of 5.2 meV. As the polariton density increases, the Rabi splitting decreases; but even when the polariton gas becomes a coherent, Bose-condensate-like state, the polaritons retain a strong exciton component, as seen in the nonlinear energy shift of the light emission. This opens up the possibility of polaritonic devices at room temperature in a material system which can be grown with very high quality and uniformity.

The full understanding of superconductivity in titanium nitride (TiN) is fundamentally important for advancing both nitride physics and high-performance superconducting quantum devices. However, further increasing its superconducting critical temperature remains a considerable challenge. In this study, we synthesized a series of high-quality TiN films with varying lattice parameters and tunable superconducting critical temperatures. Low-temperature electrical transport measurements reveal that the superconducting transition temperatures of TiN films can be increased from 5.3 to 5.7 K, a record value in the peer-reviewed literature. High-resolution x-ray diffraction analysis indicates that this increase in superconducting critical temperatures can be attributed to lattice strain. Furthermore, density functional theory calculations demonstrate that the lattice strain can effectively tune the superconductivity of TiN films by controlling the strength of the electron-phonon interaction. Our findings offer an approach to tailoring the superconducting transition temperatures of TiN films, thereby laying the groundwork for further advancements in both nitride physics and high-performance superconducting quantum devices.