The aim of this study is to theoretically investigate the loss function of ${\mathrm{layer}}_1$-hBN-${\mathrm{layer}}_2$ nanostructures, where layers 1 and 2 may be doped graphene, pristine graphene, or vacuum. This was achieved by comparing results obtained from the ab initio and massless Dirac fermion approaches and by examining how variations in the insulator thickness and system composition influence the loss function features relative to the reststrahlen bands of hexagonal boron nitride (hBN). It is shown that increasing the hBN thickness weakens plasmon coupling, leading to mode merging, while hBN's anisotropy causes phonon modes to diffuse within their reststrahlen bands, yet remain hybridized with plasmons in damping-free regions. Introducing an undoped graphene layer significantly suppresses both plasmon and phonon patterns, demonstrating that layer configuration and doping asymmetry play a key role in determining plasmon-phonon hybridization and spectral intensity.

Non-Abelian topological theory enables the classification of multigap systems and captures complex structures beyond conventional band topology. In this study, we propose a four-band non-Abelian topological insulator model in the one-dimensional ladder lattice. This model features a pair of flat bands and supports diverse edge states tunable via system parameters. More importantly, the realization in such low-complexity systems enlarges the application potential of the non-Abelian topological theory. To demonstrate this, we design a topolectrical circuit simulation scheme, laying a direct theoretical foundation for the experimental verification of non-Abelian topological insulators. Both the theoretical analysis and the simulation scheme show that the flat-band system establishes a practical, accessible platform that directly facilitates the realization and future application of non-Abelian topological phases.

We develop a pairing-based graph neural network for simulating quantum many-body systems. Our architecture augments a BCS-type geminal wave function with a generalized pair amplitude parametrized by a graph neural network. Variational Monte Carlo with our neural network simultaneously provides an accurate, flexible, and scalable method for simulating many-electron systems. We apply this method to two-dimensional semiconductor electron-hole bilayers and obtain accurate results on a variety of interaction-induced phases with one unified neural network, including the exciton Bose-Einstein condensate, electron-hole superconductor, and bilayer Wigner crystal. Our study demonstrates the potential of physically motivated neural network wave functions for quantum materials simulations.

Building on the recent success of a quantum-classical method for computing transport properties in the Holstein model with a single phonon mode [P. Mitrić et al., Phys. Rev. B 111, L161105 (2025)], we now assess its reliability in more realistic scenarios involving multiple phonon modes in the Holstein model, as well as single- and multimode Peierls models. For parameters relevant to the prototypical organic semiconductor rubrene, we compute the frequency-dependent charge mobility and find excellent agreement with results from the state-of-the-art hierarchical equations of motion method. These results show that the method, previously validated only for the single-mode Holstein model, preserves quantitative accuracy in substantially more complex and material-relevant regimes. Our microscopic approach complements the phenomenological transient-localization theory and is readily applicable to realistic electron-phonon Hamiltonians.

Point defects in two-dimensional and layered materials have attracted considerable interest as promising qubit candidates for quantum information processing due to their highly localized electronic states and spin-dependent optical properties. In this work, we use ${\mathrm{r}}^2\mathrm{SCAN}$ density functional calculations combined with complete active space self-consistent field theory to investigate bulk carbon-doped tungsten disulfide $\left({\mathrm{WS}}_2\right)$ as a potential platform for scalable quantum technologies. The meta-generalized gradient approximation exchange-correlation functional ${\mathrm{r}}^2\mathrm{SCAN}$ is found to offer a balance between accuracy and computational efficiency for specific properties, while its performance has not been tested in bulk ${\mathrm{WS}}_2$ before. By substituting sulphur atoms with carbon impurities, we achieve stable paramagnetic excited states characterized by well-defined defect levels deep within the band gap. Moreover, we investigate the zero-phonon line, radiative lifetime, and zero-field splitting due to the carbon impurities. The presence of tungsten introduces relativistic effects which are desired for some quantum applications, facilitating efficient initialization, coherent manipulation, and readout of defect spin states. We elucidate the role of carbon in lowering the emission energies into technologically relevant wavelengths for quantum information science, while we compare the present results with the extensively investigated monolayer structure. Our results highlight carbon-doped ${\mathrm{WS}}_2$ as an attractive solid-state quantum platform due to its zero-phonon line, zero-field splitting, and radiative lifetime values, enabling robust optical control and manipulation of spin states for quantum applications.

We investigate the optical response of Kekulé-Y graphene under uniaxial strain and carrier doping. Using a low-energy effective Hamiltonian, we show that strain reshapes the low-energy electronic structure of the Kekulé-Y phase and induces van Hove singularities at energies well below those of pristine graphene. Within the Kubo formalism, we calculate the optical conductivity and identify multiple anisotropic interband features, with a pronounced resonance arising from strain-induced van Hove singularities. The pronounced resonance is strongly anisotropic and robust against moderate thermal broadening and disorder, providing a clear optical signature of Kekulé-Y ordering. We further derive analytical expressions for the low-energy optical conductivity and the Drude weight, providing a detailed characterization of the strain- and doping-dependent optical response. Our results establish strain engineering as an effective route for controlling valley-dependent optical properties in Kekulé-Y graphene, originating from the Kekulé-induced coupling of the Dirac valleys, and suggest feasible optical probes for the experimental identification of the Kekulé-Y phase.

Floquet higher-order topological insulators (HOTIs), hosting robust corner-/hinge-localized states under periodic driving, represent a pivotal frontier in nonequilibrium topological physics. Although theoretical studies suggest that nonsymmorphic space-time symmetries could stabilize exotic Floquet HOTIs, experimental realization—particularly in three dimensions—has remained elusive due to the fundamental challenge of dynamically coordinating spatial and temporal coupling modulations. Here we report an experimental demonstration of both two-dimensional (2D) and three-dimensional (3D) Floquet second-order topological states using spatiotemporal topolectrical circuits. Overcoming the inherent difficulties of precise spatiotemporal control in active circuits, we implement space-time-engineered modulations via voltage-controlled time-varying impedance converters with current inversion. This enables the engineering of nonsymmorphic space-time symmetry in circuit networks and the direct observation of topological corner/hinge dynamics within Floquet quasienergy gaps. Our methodology fundamentally surpasses the conventional paradigm in photonic and acoustic systems—where spatial-axis modulation mimics pseudotemporal drives—by achieving full, dynamically coordinated spatiotemporal governance of coupling trajectories, thereby enabling the experimental synthesis of high-dimensional higher-order Floquet topological matter.

We study the ground-state phase diagram of the spin-$1/2$ antiferromagnetic Heisenberg model on the square-kagome lattice using infinite projected entangled-pair states. By systematically varying the ratio of exchange couplings on triangular and square plaquettes, we establish a complete quantum phase diagram in the thermodynamic limit. In the intermediate-coupling regime, we identify four distinct nonmagnetic phases that are unambiguously characterized as valence-bond crystals (VBCs) by their symmetry-inequivalent patterns of strong and weak spin-spin correlations. These include a plaquette crossed-dimer VBC, a loop-six VBC stabilized around the isotropic point, a generalized pinwheel VBC with reduced rotational symmetry, and a decorated loop-six VBC proximate to ferrimagnetic order. We determine the phase boundaries using a combination of bond-resolved correlation functions, entanglement entropy, and magnetization. For transitions not accompanied by sharp entanglement signatures, we extract the spin gap from finite-field simulations, allowing us to distinguish gapped and gapless VBC phases. At larger coupling ratios, the system undergoes transitions into imperfect and perfect ferrimagnetic states. Our results resolve long-standing ambiguities in the square-kagome Heisenberg model and provide a quantitatively reliable reference for future theoretical and experimental studies of frustrated quantum magnets.

The bilayer skyrmion composed of upper and lower tightly coupled skyrmions on two layers with completely compensated topological charges (called as antitopology here), has become one feasible improvement of conventional skyrmion to realize straight motion without skyrmion Hall effect, which has aroused great interest in practical applications. The present work investigates a general model (without external magnetic field) for the frustration-induced antitopological bilayer magnetic textures with rich morphologies, and discusses the modulations of key parameters on the energy barrier and the current-driven dynamics. It is revealed that the interlayer coupling plays a key role in preventing distortion, and thus helps to reach a faster velocity. This model can be realized in various frustrated magnetic materials with an antiferromagnetically coupled bilayer, providing helpful guidance for the material design and application of topological magnetic textures.

We propose Néel antiferromagnetic (AF) Mott insulators with a buckled honeycomb structure as potential candidates to host a high-temperature AF Chern insulator (AFCI). Using a generalized Kondo lattice model, we show that the staggered potential induced by a perpendicular electric field due to the buckling can drive the AF Mott insulator to an AFCI phase. We address the temperature evolution of the Hall conductance and the chiral edge states. The quantization temperature $T_q$, below which the Hall conductance is quantized, depends essentially on the strength of the spin-orbit coupling and the hopping parameter, independent of the specific details of the model. The deviation of the Hall conductance from the quantized value $e^2/h$ above $T_q$ is found to be accompanied by a spectral broadening of the chiral edge states, reflecting a finite life-time, i.e., a decay. Using parameters typical for heavy transition-metal elements we predict that the AFCI can survive up to room temperature. We suggest ${\mathrm{Sr}}_3{\mathrm{CaOs}}_2{\mathrm{O}}_9$ as a potential compound to realize a high-$T$ AFCI phase.

Recent experiments have shown that, counterintuitively, applying a magnetic field to a Wigner crystal can induce quantum Hall effects. In this Letter, we use variational Monte Carlo to show that a magnetic field can melt zero-field Wigner crystals into integer quantum Hall liquids. This melting originates from quantum oscillations in the liquid's ground state energy, which develops downward cusps at integer filling factors due to incompressibility. Our calculations establish a range of densities in which this quantum melting transition occurs.

The CoSbTe single crystal has been investigated using ab initio first-principles calculations, magnetic, heat capacity, magnetotransport, neutron diffraction, and Mössbauer measurements. Density functional theory calculations reveal band inversion with nodal-line semimetal-like crossings near the Fermi level, while surface spectral functions confirm topological surface states, evidencing a nontrivial bulk topology. Magnetic measurements of CoSbTe exhibit a nonmagnetic ground state along with trace paramagnetic impurities of ${\mathrm{Co}}^{2+}$ ions. Neutron diffraction and Mössbauer investigation also confirm the absence of any long or short range magnetic ordering above the liquid helium temperature. The electrical resistivity exhibits metallic behavior with large residual resistivity and low residual resistivity ratio. In low temperature range, resistivity dependency on temperature reveals deviation from conventional metallic $T^2$ characteristics due to presence of massive defect in the system. Transverse magnetoresistance measurements reveal a small, nonsaturating, and quasilinear field dependence. The Hall resistivity measurement indicates that the charge conduction in this compound is dominated by electrons. Our study establishes that CoSbTe is a topological nodal line semimetal candidate, making it a promising system for future exploration of topological phenomena and potential spintronic applications.

We have investigated the structural, magnetic, and transport characteristics of single-phase polycrystalline ${\mathrm{Er}}_2{\mathrm{Cu}}_2\mathrm{In}$. ${\mathrm{Er}}_2{\mathrm{Cu}}_2\mathrm{In}$ adopts a tetragonal structure reminiscent of ${\mathrm{Mo}}_2{\mathrm{B}}_2\mathrm{Fe}$-type, with a space group of $P4/mbm$ (No. 127). Below a critical temperature (${\mathrm{T}}_{\mathrm{C}}$) of 41 K, we have confirmed long-range ferromagnetic (FM) ordering through dc magnetization, specific heat capacity, and electrical resistivity. The temperature-dependent ac-magnetic susceptibility under varying excitation frequencies and ac-driven fields has shown the existence of a spin glass state below the FM transition temperature. We have employed a combination of methods, including Vogel-Fulcher, Arrhenius activation, and critical-scaling approaches, to analyze the ac-magnetic susceptibility data and estimate the dynamical parameters governing spin dynamics in ${\mathrm{Er}}_2{\mathrm{Cu}}_2\mathrm{In}$. Furthermore, the magnetoresistance exhibits significant variations around the FM transition temperature, indicative of the rich and intricate magnetic behavior inherent to ${\mathrm{Er}}_2{\mathrm{Cu}}_2\mathrm{In}$.

Surface-functionalized two-dimensional (2D) materials have garnered considerable interest owing to their emergent functional properties, including catalytic activity, ferroelectricity, and superconductivity. Here, based on first-principle calculations, we demonstrate that selenium functionalization effectively induces superconductivity in the nonsuperconducting $H$-type ${\mathrm{Mo}}_2\mathrm{B}$ ($H\text{−}{\mathrm{Mo}}_2\mathrm{B}$) monolayer. Three distinct and stable selenized MBene phases—denoted as $H_1$-, $H_2$-, and $H_3\text{−}{\mathrm{Mo}}_2{\mathrm{BSe}}_2$—are systematically identified. The incorporation of selenium significantly elevates the density of states at the Fermi level and strengthens the electron-phonon coupling (EPC). The computed EPC constants $\lambda$ for $H_1$-, $H_2$-, and $H_3\text{−}{\mathrm{Mo}}_2{\mathrm{BSe}}_2$ are 1.04, 0.73, and 1.32, respectively, yielding superconducting transition temperatures ($T_c$) of 17.80, 6.64, and 17.56 K. In addition, a nonzero topological invariant (${\mathbb{Z}}_2$ = 1) and clearly observable edge states collectively evidence nontrivial band topology in selenized ${\mathrm{Mo}}_2\mathrm{B}$ monolayer. These findings not only establish surface functionalization as an effective strategy for activating superconductivity in $H\text{−}{\mathrm{Mo}}_2\mathrm{B}$, but also position the Se-functionalized system as a compelling candidate for investigating the interplay between superconductivity and topological states in 2D materials.

We investigate the strain response of underdoped ${\mathrm{HgBa}}_2{\mathrm{CuO}}_{4+\delta }$ (Hg1201), by synchrotron X-ray diffraction and corresponding simulations of thermal diffuse scattering. The compression in the crystallographic $a$ direction leads to relatively small expansion in the $b$ and $c$ directions, with Poisson ratios ${\nu }_{\mathrm{ba}}=0.16$ and ${\nu }_{\mathrm{ca}}=0.11$, respectively. However, the Cu-O distance in the $c$ direction exhibits a notable 0.9% increase at 1.1% $a$-axis compression. We further find strain-induced diffuse scattering that corresponds to a new type of two-dimensional charge correlation. Interestingly, this signal is insensitive to the onset of superconductivity and instead corresponds to a short-range, nearly commensurate modulation with a wave vector close to (0.5,0,0) and a correlation length of approximately 4 unit cells. It closely resembles the charge order theoretically predicted in the phase diagram of the spin-liquid model with resonating valence bonds on a square lattice.

Quantum two-level systems (TLSs) commonly found at low temperature in amorphous and disordered materials are responsible for decoherence in superconducting Josephson junction qubits particularly because they absorb energy of coherent qubit oscillations in the microwave frequency range. In planar Josephson resonators with oxide interfaces, this absorption is characterized by an anomalously weak loss-tangent dependence on the field in the nonlinear regime that conflicts with the theoretical expectations and the observations in amorphous dielectrics. It was recently suggested that this anomalous absorption is caused by TLS dynamic interactions. Here, we show that such interactions cannot lead to the observed loss-tangent field dependence and suggest the alternative explanation assuming that TLS dipole moments $p$ are distributed according to the specific power law $P\left(p\right)\propto 1/p^{3-\eta }$ ($0\le \eta <1$). This assumption, indeed, results in the observed loss-tangent behavior. The hypothesis of a power-law distribution is supported both by the recent measurements of individual TLS dipole moments and the theoretical model of TLS formation because of the long-range dipole-dipole interaction, thus connecting the anomalous absorption with the possible solution of the longstanding problem of the nature of TLSs.