Motivated by the rich topology and interesting quasiband structure of twisted moiré materials subjected to light, we study a nontwisted moiré material under the influence of light. Our work is in part motivated by a desire to find an easier-to-synthesize platform that can help experimentally elucidate the interesting physics of moiré materials coupled to light. Similar to twisted moiré materials, we uncover rich topology and interesting band flattening effects, which we summarize in relevant plots such as a topological phase diagram. Our work demonstrates that much of the interesting phenomenology of twisted moiré materials under the influence of electromagnetic waves seems to be generically present even in more experimentally accessible untwisted moiré platforms, which remain highly tunable by light.

We present a mode-resolved analysis of emission thresholds in metal nanoparticles embedded within an infinite gain medium, using Mie scattering theory as a rigorous framework. Focusing on the first three resonant modes, we identify the onset of emission by locating the complex zeros of the electric scattering coefficient $a_n\left(\omega \right)$, which serve as indicators of lasing conditions. Our hybrid numerical scheme—combining coarse bracketing and two-dimensional Newton refinement—enables precise determination of both the threshold gain $G_{•n}^{\mathrm{th}}$ and corresponding emission frequency ${\omega }_{•n}^{\mathrm{th}}$ across varying particle radii. The results uncover strong size-dependent behavior, with higher-order modes in larger particles exhibiting significantly reduced threshold gain. These insights elucidate the modal dynamics underlying plasmonic nanolasing and provide design guidelines for active photonic systems leveraging gain-enhanced nanoparticles.

Sliding ferroelectricity, characterized by an out-of-plane electric polarization originating from asymmetric interlayer charge distribution in noncentrosymmetric van der Waals bilayers or multilayers, suffers from generally low polarization. Here, we propose that interface charge density enhancement is a key mechanism for increasing out-of-plane polarization in sliding ferroelectrics, which is demonstrated through first-principles calculations on two-dimensional Janus material MoSeS. The tail-to-tail stacked MoSeS bilayer (t-MoSeS) exhibits significantly larger polarization than other bilayers, which mainly origins from reduced interlayer distances and enhanced interlayer charge accumulation due to Janus structures. A systematic analysis reveals that the polarization of t-MoSeS displays heightened (reduced) sensitivity to interlayer distance (lattice constant), resulting in the Janus-induced polarization enhancement $\left(\mathrm{\Delta }P\right)$ amplified at smaller interlayer distances and lattice constants. Furthermore, we theoretically verify the scaling law $\mathrm{\Delta }P\propto P_0^2$, directly linking the polarization enhancement to the Janus monolayer polarity $\left(P_0\right)$. Our work establishes interface charge engineering as a fundamental design principle for high-polarization sliding ferroelectrics, with Janus materials providing a promising implementation pathway, resolving the structure-charge-polarization interplay and advancing the frontier of two-dimensional ferroelectric materials.

Significant progress has been achieved in the classification of topological quasiparticles after the accomplishment of large-scale searches for topological materials. However, some degeneracies in the current classification may actually lie on extended degeneracy manifolds, suggesting that a more refined classification is required. Here, we investigate accidental degeneracies of double bands (ADDBs) along high-symmetry lines in phononic systems and propose a refined classification that distinguishes the charge-0, charge-2 Dirac point, and point in nodal line (PiNL). By analyzing the symmetry constraints through group theory and compatibility relations, we identify all three types of ADDBs (charge-0, charge-2 Dirac point, and PiNL) across all space groups and high-symmetry lines. First-principles calculations on ${\mathrm{FeP}}_2$ confirm the existence of topological nodal-line phonons from ADDBs in realistic phononic materials. This work enriches our understanding of the diverse manifestations of quasiparticle excitations in topological phonon systems.

The nuclear quantum effects of hydrogen play a significant role in determining the phase stability of water ice. Hydrogen bond symmetrization occurs as hydrogen atoms tunnel in a double-well potential, ultimately occupying the midpoint between oxygen atoms and transforming ice VIII into ice X under high pressure. Quantum fluctuations lower this transition from classical predictions of more than 100 to $60\text{GPa}$. We reveal that the Perdew-Burke-Ernzerhof functional underestimates the hydrogen double-well barrier, thus resulting in a transition pressure more than $10\text{GPa}$ lower than the strongly constrained and appropriately normed functional, which is validated against quantum Monte Carlo calculations. By treating nuclear quantum anharmonicity with neural canonical transformation (NCT), we find that the transition pressure is temperature independent. Moreover, non-Gaussian flow-based wave functions predict a reduction of about $2\text{GPa}$ relative to the self-consistent harmonic approximation. Although increasing pressure typically shortens chemical bonds and hardens phonon modes, NCT calculations reveal that the hydrogen bond softens hydrogen-oxygen stretching in ice VIII under pressure.

Single-photon emitters (SPEs) are crucial for quantum technologies such as quantum simulation, secure quantum communication, and precision measurements. Two-dimensional transition-metal dichalcogenides (TMDCs) are promising SPE candidates because of their atomically thin nature and efficient photon extraction. However, their emission wavelengths limit compatibility with existing telecommunication technologies. Lanthanide doping in TMDCs, such as ${\mathrm{MoS}}_2$, offers a potential solution by introducing sharp, $f$-orbital derived emissions in the infrared range. Yet the feasibility of introducing these dopants remains uncertain due to the large ionic radii of the lanthanides. We employ density functional theory calculations to investigate the structural and electronic properties of lanthanide-doped ${\mathrm{MoS}}_2$ monolayers (Ln=Ce, Er). By evaluating formation energies with up to three adjacent S vacancies, we assess how these vacancies mitigate lattice strain caused by the size mismatch of Ce and Er with Mo. Our results show that while ${\mathrm{Ln}}_{\mathrm{Mo}}$ destabilizes the pristine lattice, S vacancies enhance thermodynamic stability. Charge-state analysis indicates that the defect states introduced by ${\mathrm{Ln}}_{\mathrm{Mo}}$ localize near the valence band and remain stable across a wide Fermi energy range. Electronic structure analysis shows that ${\mathrm{Ce}}^{4+}$ and ${\mathrm{Er}}^{3+}$ maintain their oxidation states upon electron doping due to additional acceptor states from host-induced dangling bonds. These states arise from an orbital filling mismatch between dopants and Mo. Furthermore, optical absorption analysis reveals multiple defect- and $f$-orbital-related transitions within the band gap range of the host material. In particular, ${\mathrm{Er}}_{\mathrm{Mo}}$ exhibits a weak $f\text{−}f$ absorption feature near 0.9–1.1 eV, consistent with known $4f$ transitions, while ${\mathrm{Ce}}_{\mathrm{Mo}}$ shows only defect-related absorption due to its empty $f$ shell.

The Berry curvature of phonons is an active subject of research in condensed matter physics. Here, we present a model in which phonons acquire a Berry curvature through their coupling to electrons in crystals with time-reversal symmetry. We illustrate this effect for ${\mathrm{BaMnSb}}_2$, a quasi-two-dimensional Dirac insulator, whose low-energy massive Dirac fermions generate a phonon Berry curvature that is proportional to the electronic valley Chern number. We estimate the contribution of the phonon Berry curvature to the thermal Hall conductivity in ${\mathrm{BaMnSb}}_2$.

Symmetry breaking in a layered superconductor with Ising spin-orbit coupling has offered an opportunity to realize unconventional superconductivity. To be more specific, an orbital Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, exhibiting layer-dependent finite-momentum pairing, may emerge in transition metal dichalcogenides materials (TMDC) in the presence of an in-plane magnetic field. Orbital FFLO states can be more robust against the magnetic field than the conventional superconducting state with zero-momentum pairing. This feature renders its potential in field-resilient superconducting functionality. Although an orbital FFLO state has been reported in ${\mathrm{NbSe}}_2$ and ${\mathrm{MoS}}_2$, it is not yet clear if an orbital FFLO state can be extended to other TMDC superconductors. Here, we report the transport signature of incipient orbital FFLO state in $2H-{\mathrm{NbS}}_2$ flakes and its dependence on the thickness of flakes. We conclude that the relatively weak interlayer coupling is instrumental in stabilizing orbital FFLO state at higher temperature with respect to the critical temperature and lower magnetic field with respect to paramagnetic limit in ${\mathrm{NbS}}_2$ in comparison to its ${\mathrm{NbSe}}_2$ counterpart.

In superconductor-semiconductor hybrids, applying a magnetic field closes a trivial bulk gap and causes a topological phase transition (TPT), resulting in the emergence of Majorana zero modes at both ends of the wires. However, trivial Andreev bound states formed at the interface with metallic leads mimic the local Majorana properties, making it difficult to detect the TPT through local conductance measurements. In this work, we investigate the detection of the TPT by exploiting the static and dynamical density response of the hybrid system. In particular, we demonstrate that the dynamical renormalized responses, the density response including the effect of Coulomb interactions, reveal the characteristic electronic structure and detect the TPT, which we then show to produce strong intensities of Raman scattering. Furthermore, we find that gapless plasmons emerge in the normal state, signaling the bulk Lifshitz transition. Our results thus predict that the bulk response of superconducting nanowires is a powerful spectroscopic approach to detect the bulk topological phase transition.

Without external influences, electrons within an atom typically reside in the ground state, characterized by the lowest possible values of the principal and orbital angular momentum quantum numbers, 1 and 0, respectively. Recent studies have shown that the introduction of gauge flux into an artificial crystal plaquette can induce topological Wannier cycles originating from $1s$-like orbitals. However, the exploration of topological Wannier cycles involving complex orbits remains an open question. In this work, we experimentally realize topological dual-Wannier cycles, driven by the insertion of gauge flux into an orbital phononic crystal. This phononic crystal comprises disk-shaped acoustic cavities connected by pairs of parallel tubes, supporting $2s$-, $3p$-, and $4d$-like orbitals. The insertion of gauge flux is achieved by introducing a step screw dislocation, which induces cyclic spectral flows that bridge higher-order topological band gaps. By combining the orbital degree of freedom, these cyclic spectral flows give rise to dual-topological boundary states localized at the dislocation core. Our findings not only deepen the understanding of artificial gauge flux but also open new avenues for exploring orbital-related phenomena in classical wave systems.

X-ray photon correlation scattering measurements are undertaken on a thermally active artificial spin ice based on the square lattice, referred to as artificial square ice, to probe the fluctuation timescales as a function of temperature as the system passes through the paramagnetic-antiferromagnetic phase transition, which belongs to the two-dimensional Ising universality class. In the paramagnetic regime, a single exponential timescale is seen, whereas at and below the critical temperature, a stretched exponential decorrelation is observed, with the stretching exponent decreasing from unity down to below one-half as the temperature reduces. This trend is confirmed by kinetic Monte Carlo simulations of a simplified point-dipolar square ice system, and is in agreement with past theoretical work on the kinetic Ising model where stretched exponential relaxation due to equilibrium domain wall dynamics below the critical temperature was found.

The ballistic orbital current $\left(J_L\right)$ promises more efficient information transfer over longer distances in various materials compared with spin current $\left(J_S\right)$. However, experimental observation and quantitative investigation of ballistic orbital transport remain elusive due to the entanglement between $J_L$ and $J_S$. Here, we show that the vanishingly small spin-orbit coupling of Cu and its negligible $d$-orbital character close to the Fermi energy allow spin-independent orbital investigation. Combined with theoretical and experimental results, we reveal that the ballistic transport length of $J_L$ generated by Cr reaches up to 13 nm, a magnitude larger than the typical spin-diffusion length of 1–2 nm. Moreover, an orbital efficiency of 0.44 was quantitatively determined in Cr, which is 1.9 times larger than that of spin-dominated heavy metal Pt. These results not only provide a convenient approach for the quantitative study of $J_L$ but also highlight the significant potential of orbital engineering in spin-orbitronics applications.

The depairing limit and the vortex-free state in a superconductor is crucial for both the study of supercurrent related physics and the application eliminating noise linked to vortex motion. In this work, we report the evidence of depairing limit and the vortex-free state achieved by geometric constraint in FeSe superconductors. A series of narrow bridges with varying widths at the same location of a single crystal were prepared by the “pickup” method using successive focused ion beam millings. By simply reducing the width of bridge, the magnitude of critical current density $\left(J_{\mathrm{c}}\right)$ is enhanced more than one order, evidencing the achievement of depairing limit. Moreover, in the bridge with a width smaller than the penetration depth $\left(\lambda \right)$, $J_{\mathrm{c}}$ is found to be robust against magnetic field up to 1 kOe. The field-robust $J_{\mathrm{c}}$ is a strong piece of evidence for vortex-free state, which is created by the enhancement of lower critical fields due to geometric constraint.

We investigate the spectrum of Andreev bound states and supercurrent in a $p$-wave non-Hermitian Josephson junction (NHJJ) in one dimension. The studied NHJJ is composed of two topological $p$-wave superconductors connected by a non-Hermitian dissipative junction. Starting from the effective non-Hermitian Bogoliubov–de Gennes bulk Hamiltonian, we find that a pair of exceptional points emerge in the complex spectrum of Andreev quasibound states. The two exceptional points with zero energy locate symmetrically with respect to the Josephson phase difference $\varphi =\pi$, at which a Majorana zero mode persists. Notably, the exceptional points descend from a pair of Majorana zero modes after turning on the non-Hermiticity and are topologically protected. By analyzing the non-Hermitian scattering process at the junction, we explicitly demonstrate the loss of quasiparticles through the decay of scattering amplitude probabilities. Furthermore, we obtain the supercurrent directly by the inelastic Andreev reflection amplitudes, which provides a more intuitive interpretation of the transport properties in NHJJs. The supercurrent varies continuously as a function of $\varphi$ across the exceptional points. No enhancement of critical current is observed. We also generalize our analysis to a mixed $s\text{−}p$ wave NHJJ. Our results provide rich insights on the transport properties of Josephson junctions in the presence of Majorana zero modes, exceptional points, and non-Hermiticity.

The breathing kagome lattice, a variant of the kagome structure characterized by inversion-symmetry breaking and geometric frustration, provides a fertile ground for realizing unconventional electronic functionalities. Here, using first-principles calculations, we identify 18 stable two-dimensional $M_3{QX}_7$ compounds ($M=\mathrm{Nb}$,Ta; $Q=\mathrm{S}$,Se,Te; $X=\mathrm{Cl}$,Br,I) that host transition-metal-based breathing kagome motifs. Unlike their Mott-insulating, isostructural $M_3{X}_8$ counterparts, these $M_3{QX}_7$ monolayers are nonmagnetic semiconductors driven by molecular-orbital splitting in embedded $M_3{X}_{12}Q$ clusters. Remarkably, a pronounced Rashba spin splitting (RSS) appears in the lowest conduction band (LCB) and can be effectively tuned via biaxial strain. A k · p analysis shows that the electronic state of the LCB at the Γ point transforms as the $E_{1/2}$ double-group representation of the $C_{3v}$ point group, thereby permitting linear-in-$k$ spin-orbit coupling terms that produce the observed RSS. Moreover, $M_3{QX}_7$ monolayers display the rare coexistence of in-plane and out-of-plane piezoelectric responses, in contrast to conventional two-dimensional piezoelectrics whose polarization is confined to the basal plane. The out-of-plane dipole moment (${\mu }_{\mathrm{z}}$) and the surface asymmetry in Born effective charges ($|Z_{\mathrm{Bottom}}^{*}-Z_{\mathrm{Top}}^{*}|$) serve as quantitative descriptors of the vertical piezoelectric response, providing a microscopic understanding of its origin. Due to the exceptional mechanical flexibility of this system, both in-plane and out-of-plane responses reach sizeable magnitudes. These findings not only demonstrate the potential of $M_3{QX}_7$ monolayers for integration into spintronic and piezotronic devices, but they also offer new insights into emergent properties in intrinsically inversion-symmetry-broken breathing kagome lattices.

We address theoretically edge-emitting semiconductor lasers based on a multilayer waveguide structure in a form of a distributed Bragg reflector (DBR) and emitting laser light in a TM-polarized surface-trapped optical mode (optical Tamm state, OTS) which decays exponentially into the air and decays in an oscillatory way into the DBR. The effective refractive index of the lasing mode is close to 1, which renders the mode reflectivity from an uncoated (as-cleaved) facet anomalously small. The facet reflectivity is calculated exactly by the finite difference frequency domain method. We show that the exact reflectivity differs drastically from the value found in the Fresnel approximation. The reflectivity in a range of 0.01–0.07 shows that the uncoated facet is naturally antireflective for the lasing surface-trapped mode. A strong dependence of the facet reflectivity on the wavelength of light affects the threshold lasing conditions and the wavelength at which the lasing first occurs. A metal bar mounted on top of the DBR close to the rear facet forms a moderately highly reflecting mirror for the surface-trapped mode. The model structure of a semiconductor laser is proposed, in which the TM-polarized OTS has the preferred conditions for the lasing versus all other modes. Two types of lasers are considered: (i) a laser with the naturally antireflective uncoated front facet and a metal bar mirror on the top surface close to the rear facet and (ii) a laser with metal bar mirrors close to both facets. For a laser emitting at $\lambda \approx 1\mu \mathrm{m}$ the lasing mode has the penetration depth to the air about $0.7–1.3\mu \mathrm{m}$ which allows an efficient near-field outcoupling to an external waveguide or to an optical fiber placed in the vicinity of the DBR surface.

The dynamics of edge states in topological diffusive systems are studied. Concrete calculations are performed using a honeycomb lattice consisting of two sublattices with nonuniform capacities, which is described by the mass term of the Dirac equation. We find that the time evolution of both arm-chair and zig-zag edge states, which are the mass domain walls separating the positive and negative mass regions, give rise to diffusive currents that flow parallel to the edge. From both numerical and analytical calculations, we find that the periodicity of the edge current differs between the zig-zag edge and the arm-chair edge, and the current magnitude decreases as the mass term becomes smaller and the domain wall width grows larger. Finally, these behaviors are verified by simulations of heat diffusion in topological edge states.

Group IV quantum dot hole spin systems, exhibiting strong spin-orbit coupling, provide platforms for various qubit architectures. The rapid advancement of solid-state technologies has significantly improved qubit quality, including the time scales characterizing electrical operation, relaxation, and dephasing. At this stage of development, understanding the relations between the underlying spin-orbit coupling and experimental parameters, such as quantum dot geometry and external electric and magnetic fields, has become a priority. Here we focus on a Ge hole double quantum dot in the Pauli spin blockade regime and present a complete analysis of the leakage current under an out-of-plane magnetic field. By considering a model of anisotropic in-plane confinement and $k^3$-Rashba spin-orbit coupling, we determine the behavior of the leakage current as a function of detuning, magnetic field magnitude, interdot distance, and individual dot ellipticities. We identify regions in which the leakage current can be suppressed by quantum dot geometry designs. Most importantly, by rotating one of the quantum dots, we observe that the quantum dot shape induces a strongly anisotropic leakage current. These findings provide guidelines for probing the spin-orbit coupling, enhancing the signal-to-noise ratio, and improving the precision of Pauli spin blockade readout in hole qubit architectures.