We investigate the dynamics of the Su-Schrieffer-Heeger model with boundary dissipation described by Lindblad master equations and unravel distinct dynamical features in the topologically different phases of the underlying Hamiltonian. By examining the long-time damping dynamics, we uncover a dynamical duality phenomenon between the weak and strong dissipation regions which exists only in the topologically nontrivial phase, linked to the structure of the Liouvillian spectra, particularly the stripe closest to the steady state. When dissipation is confined to a single boundary, the dynamical duality phenomenon still exists. Under this condition, the Liouvillian gap fulfills an exponential size scaling relation in the topologically nontrivial phase and a power-law size scaling relation in the topologically trivial phase. Within the topologically nontrivial region, we identify the existence of boundary-localized dark states in the thermodynamical limit, which are responsible for the exponential size decay of Liouvillian gap.

We write down a class of two-dimensional quantum spin-$\frac{1}{2}$ Hamiltonians whose eigenspectra are exactly solvable via the Jordan-Wigner transformation. The general structure corresponds to a suitable grid composed of XY or X-Ising spin chains and Z-Ising spin chains and is generalizable to higher dimensions. They can host stacks of one-dimensional spinless fermion liquids with gapless excitations and power-law correlations coexisting with ordered spin moments (localized spinless fermions). Bond-dependent couplings thus can be an alternate mechanism than geometric frustration of $SU\left(2\right)$-symmetric couplings to obtain spinless fermionic excitations. Put in a different way, bond-dependent couplings allow for an embedding of one-dimensional spinless fermion (Tomonoga-Luttinger) liquids and solids and also Majorana excitations in higher dimensions. They can accommodate a simpler set of site-local conserved quantities apart from the more intricate, interlocked set of plaquette-local or bond-local conserved quantities in Kitaev's honeycomb model with Majorana excitations. The proposed grid structure may provide an architecture for quantum engineering with controllable qubits.

We propose a family of modulated honeycomb lattices, a class of quasiperiodic tilings characterized by the metallic mean. These lattices consist of six distinct hexagonal prototiles with two edge lengths, $\ell$ and $s$, and can be regarded as a continuous deformation of the honeycomb lattice. The structural properties are examined through their substitution rules. To study the electronic properties, we construct a tight-binding model on the tilings, introducing two types of hopping integrals, $t_L$ and $t_S$, corresponding to the two edge lengths, $\ell$ and $s$, respectively. By diagonalizing the Hamiltonian on these quasiperiodic tilings, we compute the corresponding density of states (DOS). Our analysis reveals that the introduction of quasiperiodicity in the distribution of hopping integrals induces a spiky structure in the DOS at higher energies, while the linear DOS at low energies ($E\sim 0$) remains robust. This contrasts with the smooth DOS in the disordered tight-binding model, where two types of hopping integrals are randomly distributed according to a given ratio. Furthermore, we study the magnetic properties of the Hubbard model on modulated honeycomb lattices by means of real-space Hartree approximations. A magnetic phase transition occurs at a finite interaction strength due to the absence of the noninteracting DOS at the Fermi level. When $t_L\sim t_S$, the phase transition point is primarily governed by the linear DOS. However, far from the condition $t_L=t_S$, the quasiperiodic structure plays a significant role in reducing the critical interaction strength, which is in contrast to the disordered system. Using perpendicular space analysis, we demonstrate that sublattice asymmetry inherent in the quasiperiodic tilings emerges in the magnetic profile, providing insights into the interplay between quasiperiodicity and electronic correlations.

We study the out-of-equilibrium dynamics of one-dimensional quantum Ising models in a transverse field $g$, driven by a time-dependent longitudinal field $h$ across their magnetic first-order quantum transition at $h=0$, for sufficiently small values of $\left|g\right|$. We consider nearest-neighbor Ising chains of size $L$ with periodic boundary conditions. We focus on the out-of-equilibrium behavior arising from Kibble-Zurek protocol, in which $h$ is varied linearly in time with a timescale $t_s$, i.e., $h\left(t\right)=t/t_s$. The system starts from the ground state at $h_i\equiv h\left(t_i\right)<0$, where the longitudinal magnetization $M$ is negative. Then it evolves unitarily up to positive values of $h\left(t\right)$, where $M\left(t\right)$ becomes eventually positive. We identify several scaling regimes characterized by a nontrivial interplay between the size $L$ and the timescale $t_s$, which can be observed when the system is close to one of the many avoided level crossings that occur for $h\ge 0$. In the $L\to \infty$ limit, all these crossings approach $h=0^{+}$, making the study of the thermodynamic limit, defined as the limit $L\to \infty$ keeping $t$ and $t_s$ constant, problematic. We study this limit numerically, by first determining the large-$L$ quantum evolution at fixed $t_s$, and then analyzing its behavior with increasing $t_s$. Our analysis shows that the system switches from the initial state with $M<0$ to a positively magnetized state at $h=h_{★}\left(t_s\right)>0$, where $h_{★}\left(t_s\right)$ decreases with increasing $t_s$, apparently as $h_{★}\sim 1/ln{t}_s$. This suggests the existence of a scaling behavior in terms of the rescaled time $\mathrm{\Omega }=tln{t}_s/t_s$. The numerical results also show that the system converges to a nontrivial stationary state in the large-$t$ limit, characterized by an energy significantly larger than that of the corresponding homogeneously magnetized ground state.

The crystal and magnetic structures of antiferromagnetic Mn deuterides formed by hydrogenating Mn metal at high temperature and high pressure, fcc γ-$\mathrm{Mn}{\mathrm{D}}_x$ and hcp ε-$\mathrm{Mn}{\mathrm{D}}_{x^{\prime }}$, were investigated using in situ neutron powder diffraction. Deuterium atoms partially occupied the octahedral interstitial positions of the fcc and hcp metal lattices. The site occupancies increased rapidly with decreasing temperature from the deuteride formation temperatures of 875–900 K to approximately 450 K and remained at steady values down to 300 K. The Néel temperature of 543(10) K was determined for γ-$\mathrm{Mn}{\mathrm{D}}_{0.34}$ from the appearance of a magnetic scattering peak during decreasing temperature. For ε-$\mathrm{Mn}{\mathrm{D}}_{0.62}$, the saturation magnetic moment and Néel temperature were determined to be 0.82(1)${\mu }_{\mathrm{B}}$ and 347(3) K, respectively, from the variations of magnetic moment with temperature. The Néel temperatures determined for γ-$\mathrm{Mn}{\mathrm{D}}_{0.34}$ and ε-$\mathrm{Mn}{\mathrm{D}}_{0.62}$ are consistent with those predicted by the respective Slater-Pauling curves proposed in previous studies based on the rigid-band model. These updated Néel temperatures provide insight into the development of more accurate Slater-Pauling curves based on electronic band structure calculations.

Employing temperature ($T$)-dependent angle-resolved photoemission spectroscopy (ARPES) near the Ce $4d$ absorption edge, we have investigated the electronic structures of the strongly correlated Kondo insulators (KIs) and/or Kondo semimetals of CeNiSn and $\text{CeRh}X$ ($X$=As, Sb), which also belong to potential topological KIs (TKIs). Good agreement is found between the Fermi surfaces (FSs) measured at the Ce $4d\to 4f$ on resonance and those calculated and unfolded into the Ce-only Brillouin zone, supporting the crucial Ce $4f$ contribution to the Fermi-edge states in them. While the FSs of CeRhSb and CeNiSn are similar to each other, they are quite different from those of CeRhAs, which is understood to originate from the semimetallic Kondo ground states of CeNiSn and CeRhSb in contrast to the insulating Kondo ground state of CeRhAs. $T$-dependent ARPES demonstrates the existence of the Kondo resonance above the Fermi level ($E_F$) and its $T$-driven decoherence in CeNiSn and CeRhSb, and the existence of the Ce $4f$ Kondo-like peak well below $E_F$ with a pseudogap in CeRhAs. With increasing $T$, the tail of the Kondo resonance in CeNiSn and CeRhSb loses its coherence, whereas the Ce $4f$ Kondo-like peak in CeRhAs persists up to $T\ge 200$ K. The Kondo temperatures ($T_K\mathrm{s}$) are estimated via the analysis of $T$-dependent ARPES, yielding $T_K\approx 80$ K (CeNiSn), $T_K\approx 180$ K (CeRhSb), and $T_K\gg 200$ K (CeRhAs). High-resolution, low-$T$ ARPES confirms the Kondo resonance just above $E_F$ in CeNiSn and CeRhSb Kondo semimetals and the KI ground state of CeRhAs with a pseudogap of $\mathrm{\Delta }\approx 30$ meV, demonstrating the importance of the coherent Kondo states in determining their potential topological properties. The differences in the $T$-dependent ARPES of CeNiSn and CeRhSb suggest the weaker $f\text{−}c$ hybridization in CeNiSn than in CeRhSb ($c$: conduction electron), which is likely due to the more localized Ni $3d$ orbitals than the delocalized Rh $4d$ orbitals. The differences between the $T$-dependent ARPES of CeNiSn/CeRhSb Kondo semimetals and those of CeRhAs Kondo insulator are likely due to the smaller volume of CeRhAs than those of CeNiSn/CeRhSb.

The multiexciton optical gain that stems from the multiple degeneracies of quantum dot (QD) band-edge states, along with the rapid multiexciton Auger recombination, results in a high lasing threshold for colloidal QD lasers, limiting their practical applications. In this article, we propose an approach to achieving a “zero-threshold” optical gain by controlling doping concentration via the QD size. By using $\mathrm{A}{\mathrm{g}}_2\mathrm{Se}$, HgSe, and HgS QDs, zero-threshold optical gain was achieved across most wavelengths in the near-infrared and short-wave infrared regions. We established kinetic equations to describe a coupled QD-light-field system, which consists of QDs with varying doping concentrations. Based on this, we calculated the lasing thresholds for the three types of QDs with specific diameters. The results show that by significantly suppressing Auger recombination with the core/alloy/shell structure, pulsed lasing with an average QD occupancy threshold of approximately 0.17, and continuous-wave lasing with a threshold pump intensity of approximately $0.5\mathrm{kW}{\mathrm{cm}}^{-2}$ can be achieved. This work presents an air-stable approach to realize “zero-threshold” optical gain and develops a theoretical model to confirm the feasibility of this approach.

The layer-resolved quantum transport response of a twisted bilayer graphene device is investigated by driving a current through the bottom layer and measuring the induced voltage in the top layer. Devices with four- and eight-layer differentiated contacts are analyzed, revealing that in a nanoribbon geometry (four contacts), a longitudinal counterflow current emerges in the top layer, while in a square-junction configuration (eight contacts), this counterflow is accompanied by a transverse, or Hall, component. These effects persist despite weak coupling to contacts, on-site disorder, lattice relaxation, and variations in device size. The observed counterflow response indicates a circulating interlayer current, which generates an in-plane magnetic moment excited by the injected current. Finally, due to the intricate relationship between the electrical layer response, energy, and twist angle, a clusterized machine learning model is trained, validated, and tested to predict various conductances.

Graphene, renowned for its exceptional electronic and optical properties as a robust two-dimensional (2D) material, traditionally lacks electronic correlation effects. Proximity coupling offers a promising method to endow quantum materials with novel properties. In this study, we realized a 2D heterostructure by intercalating Sn into zero layer graphene on SiC(0001), allowing us to explore the coupling between a correlated 2D electron gas and a Dirac metal. This results in the stabilization of Sn-$\sqrt{3}$ superlattice structures at the interface, which reveal Mott-Hubbard bands, in qualitative agreement with both experimental observations and theoretical predictions.

Layer Hall effect, where electrons can deflect to opposite directions in different layers of layered antiferromagnetic materials, is a promising physical phenomenon in future spatial-resolved layertronics application. Here, we demonstrate that multiple layer Hall states including layer-polarized Hall, quantized anomalous layer Hall (QALH), and nearly high-Chern-number QALH effects can be sequentially realized in the ${\text{V}}_2{\text{WS}}_4$ magnetic topological insulator family. First, with applied external electric field and increased field strength to 0.4 V/Å, layer-polarized Hall and QALH effect with fully quantized Hall conductivity plateau ${\sigma }_{xy}=e^2/h$ begins to appear in the ${\text{V}}_2{\text{WS}}_4$ bilayer. Furthermore, by tuning the electric field direction and Fermi level, QALH effect can be effectively switched between layers and the number of peaks in Hall conductivity ${\sigma }_{xy}$ exhibits a pronounced parity-dependent behavior. Remarkably, through synergetic modulation of external magnetic and electric fields, a nearly high-Chern-number QALH effect can be observed in an odd-layer ${\text{V}}_2{\text{WS}}_4$ system. The above findings provide a nearly ideal topological magnet family harboring various layer Hall effects especially with fully quantized-layered transport.

The intrinsic properties of two-dimensional (2D) layered materials can be effectively tuned by controlling the intercalation species. Here, we have adopted first-principles and high-throughput calculations to study the 78 types of $X$-intercalated ($X=\text{Be}$, Mg, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Y) bilayer blue phosphorus. Among them, $ACaB$, ${AScA}^{\prime }$, and ${AYA}^{\prime }$ stacking configurations exhibit very strong superconductivity with a reliable stability. The superconducting transition temperature $T_c$ of $ACaB$ is estimated to 30.11 K, and further improved to 33.83 K under a tensile strain of 1%. In addition, ${AScA}^{\prime }$ and ${AYA}^{\prime }$ possess a $\mathit{T}{}_c$ of about 20.35 and 28.45 K, respectively. Remarkably, the superconductivity in $X$-intercalated bilayer blue phosphorus arises from the electron-phonon coupling (EPC) between the outermost electrons of the intercalated metals and the in-plane phonon modes of phosphorus. Furthermore, the EPC strength is directly proportional to the electronegativity difference between the intercalated metal and the phosphorus atom. In addition, the different stacking configurations also play an important role in the superconductivity of $X$-intercalated blue phosphorus. Our work sheds light on the exploration of high $\mathit{T}{}_c$ superconductors in 2D semiconductors through intercalations.

The emerging field of valleytronics harnesses the valley degree of freedom of electrons, akin to how electronic and spintronic devices utilize the charge and spin degrees of freedom of electrons, respectively. The engineering of valleytronic devices typically relies on the coupling between valley and other degrees of freedom such as spin, giving rise to valley spintronics where an external magnetic field manipulates the information stored in valleys. Here, a valley gapless semiconductor is proposed as a potential electrically controlled valleytronic platform because the valley degree of freedom is coupled to the carrier type, i.e., electrons and holes. The valley degree of freedom can be electrically controlled by tuning the carrier type via the device gate voltage. We demonstrate the proposal for realizing a valley gapless semiconductor in the honeycomb lattice with the Haldane and modified Haldane models. The system's valley-carrier coupling is further studied for its transport properties in an all-electrically controlled valley filter device setting. Our work highlights the significance of the valley gapless semiconductor for valleytronic devices.

The surface tunneling microscope (STM) method probes the conduction electron spectrum which is influenced by the presence of collective order parameters. It may, in fact, be used as a tool to obtain important information about their microscopic nature, for example, the gap symmetry in unconventional superconductors. Surprisingly, it has been found that the STM spectrum can also identify magnetic order of completely localized electrons e.g., an incommensurate helical structure of $4f$ electron moments, as observed in the compound ${\mathrm{GdRu}}_2{\mathrm{Si}}_2$. This is due to the fact that the exchange coupling of conduction states to the localized subsystem reconstructs the conduction bands which then leaves an imprint on the STM spectrum. First, we develop a theory based on this idea that shows the appearance of STM satellite peaks at the wave vector of localized moment helical order for the pure surface. Second, we derive the quasiparticle interference spectrum in the Born approximation due to the presence of surface impurities which contain information on the reconstruction process of itinerant states caused by the localized helical order. Furthermore, we show that within the full $T$ matrix approach, impurity bound states are also influenced by the exchange coupling to helical magnetic order.

We investigate the intrinsic spin Nernst effect (SNE), a transverse spin current induced by temperature gradients, in topological Dirac semimetals (TDSMs) and magnetic Weyl semimetals (MWSMs) with Ising spin-orbit coupling. The intrinsic SNE is described by the spin Berry curvature, which reflects the geometric nature of TDSMs and MWSMs. We clarified that the intrinsic SNE becomes significant when the Fermi energy is near, but slightly deviates from, the energy of the point nodes. In this situation, Bloch electrons with strong spin Berry curvature contribute to the SNE while avoiding carrier compensation between electrons and holes. We found that in TDSMs with small Fermi surfaces, the spin Nernst angle, which measures the efficiency of the SNE, is larger than that observed in heavy metals. This suggests that TDSMs with small Fermi surfaces can achieve efficient heat-to-spin current conversion. In MWSMs, variation in the magnitude of the exchange coupling with magnetic moments significantly changes the SNE, affecting both the direction and magnitude of the spin Nernst current. This implies that ferromagnetic transitions can be used to reverse the spin Nernst current. These results provide the fundamentals for future topological spin caloritronics.

${\mathrm{Bi}}_4{\mathrm{Br}}_4$ is a prototypical quasi-one-dimensional (1D) material in which covalently bonded bismuth bromide chains are arranged in parallel, side-by-side and layer-by-layer, with van der Waals (vdW) gaps in between. So far, two different structures have been reported for this compound, $\alpha \text{−}{\mathrm{Bi}}_4{\mathrm{Br}}_4$ and $\beta \text{−}{\mathrm{Bi}}_4{\mathrm{Br}}_4$, in both of which neighboring chains are shifted by $\mathbf{b}/2$, i.e., half a unit-cell vector in the plane, but which differ in their vertical stacking. While the different layer stacking is known to result in distinct electronic properties—higher-order and weak topological insulators, respectively—the effect of different in-plane arrangements of the atomic chains remains an open question. Here, using scanning tunneling microscopy and spectroscopy (STM/STS), we report an unusual ${\mathrm{Bi}}_4{\mathrm{Br}}_4$(001) structure, with a shift of $\mathbf{b}/3$ between neighboring chains in the plane and AB layer stacking. We determine shear strain to be the origin of this structure, which can readily result in shifts of neighboring atomic chains because of the weak interchain bonding. For the observed $b/3$ structure, the (residual) atomic chain shift corresponds to an in-plane shear strain of $\gamma \approx 7.5\%$. STS reveals a bulk insulating gap and metallic edge states at monolayer surface steps, indicating that, just like for $\alpha \text{−}{\mathrm{Bi}}_4{\mathrm{Br}}_4$, monolayers of the $b/3$ structure are also quantum spin Hall insulators, in agreement with density functional theory (DFT) calculations.