Guided by the contact polygon method, we establish a topological design principle for constructing periodically dome-shaped graphene (PDG). Integrating different membered nonhexagonal carbon rings into honeycomb frameworks of the PDGs induces spontaneous surface positive or negative Gaussian curvature, with the former yielding tunable Poisson's ratios for small membered rings and the latter dictating strong full negative Poisson's ratio behavior for large membered rings. Furthermore, the PDG with five-membered rings exhibits both a nearly full zero Poisson's ratio and superhigh electron mobility of $91\times {10}^4{\text{cm}}^2{\text{V}}^{-1}{\text{s}}^{-1},$ which is three times that of graphene. Building upon these PDGs, structural modifications are introduced to extend their functionalities. Modified PDG with a mirror symmetry plane and ${sp}^2\text{−}{sp}^3$ carbon bonding is found to suppress the lattice thermal conductivity of two-dimensional (2D) carbon networks to a new low level (40 ${\mathrm{W}\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$) via low-lying optical-acoustic phonon intersections and large acoustic phonon softening, while BN codoped PDG with a composition of ${\text{C}}_2\text{BN}$ demonstrates a superconducting transition temperature of 22 K fueled by a Fermi-level Van Hove singularity. This study establishes a new bridge between structural topology and advanced functionalities of multifunctional 2D carbon networks.

We show that the quantum geometry of fractionalized spin excitations in Mott-insulating quantum spin liquids (QSLs) gives rise to a finite Raman circular dichroism (RCD) signal. We identify conditions under which the Loudon-Fleury framework, where light modulates the underlying exchange interactions, and the light-matter-coupling approach, where the effective vector potential couples directly to the spinon bands, yield equivalent Raman vertices for the fractionalized quasiparticles. Using the latter, we derive an analytical decomposition of the RCD into different quantum geometric contributions. This reveals the sensitivity of the RCD to the underlying structure of the wave functions and the handedness of the excitations, rather than a nonzero Chern number of spinon excitations. To illustrate this, we apply our approach to two examples, the Kitaev honeycomb model in a magnetic field and a parton mean-field state of the chiral QSL on the triangular lattice.

We theoretically study the non-Hermitian topology of magnons with finite lifetimes due to Gilbert damping. By incorporating the spin-wave theory and perturbation theory for the Landau-Lifshitz-Gilbert equation including nonlocal damping terms, we analytically evaluate the spectral winding number for point gaps, which indicates the existence of the non-Hermitian skin effect (NHSE). We find that, in noncollinear magnetic textures, the NHSE can occur even in the absence of nonlocal damping, due to the momentum-dependent mixing of the particle and hole components of magnon eigenmodes, which is absent in collinear magnets with a single magnon band. In the presence of nonlocal damping along one direction, we show that the winding number for an energy band with a unique minimum is determined from the sign of the wave number at the band minimum. We demonstrate these results using a model that hosts a skyrmion-string lattice as a steady state. We further investigate spin-wave propagation dynamics excited by a magnetic-field pulse and show that the propagation direction changes drastically from band to band depending on the presence of local and nonlocal damping, consistent with the nontrivial winding numbers.

We derive a microscopic theory of drag for a Bose–Einstein condensate interacting with a moving reservoir. Starting from interactions between a condensate and a drifting fermionic bath, we integrate out the bath degrees of freedom within the Born–Markov approximation to obtain an effective Gross–Pitaevskii equation with a drag potential. From this potential we derive an effective drag force and obtain a closed expression for the drag coefficient, determined by the reservoir density fluctuations and the condensate density profile. As an application, we simulate the drag for an exciton–polariton condensate interacting with a drifting electron gas.

The atomistic mechanisms governing solvent-mediated exfoliation of transition metal dichalcogenides remain poorly understood, limiting the rational design of scalable synthesis strategies. Here we investigate the role of hydrazine (${\mathrm{N}}_2{\mathrm{H}}_4$) in the liquid-phase exfoliation of ${\mathrm{TiSe}}_2$ and copper-intercalated ${\mathrm{TiSe}}_2$ (${\mathrm{Cu}}_x{\mathrm{TiSe}}_2$), is investigated combining density functional theory (DFT) calculations with experimental solvothermal synthesis under subcritical conditions. ${\mathrm{N}}_2{\mathrm{H}}_4$ is found to physisorb on pristine ${\mathrm{TiSe}}_2$ but chemisorb on ${\mathrm{Cu}}_x{\mathrm{TiSe}}_2$, driven by the formation of an N-Cu bond. This enhanced chemical affinity, rather than a simple geometric expansion of the interlayer spacing, is identified as the primary driver of the selective, copper-promoted exfoliation observed experimentally. ${\mathrm{N}}_2{\mathrm{H}}_4$ intercalation further increase the equilibrium interlayer separation and reduces the exfoliation energy. AFM characterization confirms the synthesis of monolayer ${\mathrm{Cu}}_x{\mathrm{TiSe}}_2$ sheets. These results reveal the key interactions that enable ${\mathrm{N}}_2{\mathrm{H}}_4$-assisted exfoliation of ${\mathrm{TiSe}}_2$ and its copper-intercalated analogs.

The low-temperature thermal properties of amorphous solids, from the tunneling regime to the boson peak (BP), are described in terms of the redistribution of low-energy excitations induced by structural disorder and the progressive loss of vibrational coherence. We develop an interacting two-level-system (ITLS) model based on a coarse-grained three-level Hamiltonian that provides an effective representation of two classes of low-energy excitations: localized tunneling excitations and higher-energy excitations arising from their coupling with elastic vibrations. From the corresponding equilibrium partition functions, we derive the specific heat and construct an effective thermodynamic spectral density that describes the temperature-dependent redistribution of spectral weight between localized and progressively hybridized excitations. Within this picture, the experimentally established excess of vibrational states remains fully consistent with the present description. The ITLS framework further resolves its thermodynamic signature into a low-energy soft contribution, which already develops a boson-peak-like maximum, and higher-energy hybridized contributions that are required to reproduce the complete experimental peak. A finite coherence length $\xi$ introduces an effective cutoff frequency ${\nu }_{\mathrm{off}}$ that delimits the thermodynamically active spectral window. Fits to specific-heat measurements for several glass-forming systems reproduce the experimental behavior over the temperature range considered and yield cutoff frequencies comparable to reported Ioffe–Regel crossover frequencies. Our results provide a unified equilibrium thermodynamic description of the tunneling regime and the boson peak and connect their spectral signatures with the progressive loss of vibrational coherence in disordered solids.

We investigate the fate and robustness of topological strong zero modes (SZMs) in random Ising-Majorana chains using the SZM fidelity ${\mathcal{F}}_{\mathrm{SZM}}$ as a many-body diagnostic that quantifies how accurately SZM operators map the entire spectrum between opposite parity sectors. In clean systems, ${\mathcal{F}}_{\mathrm{SZM}}=1$ in the topological phase, vanishes in the trivial regime, and takes the universal value $\sqrt{8}/\pi$ at the $(1+1)$-dimensional Ising critical point. Here we study how quenched disorder modifies this picture across the infinite-randomness fixed point (IRFP) governing the criticality of the random chain. In both microcanonical and canonical ensembles, SZMs persist throughout the topological phase, including the gapless Griffiths regime, with fidelities converging exponentially to unity. At the IRFP, however, the fidelity distributions become ensemble dependent: the microcanonical ensemble displays bimodal peaks at $\{0.5,1\}$, while the canonical ensemble develops a triple-peak structure at $\{0,0.5,1\}$ with power-law singularities. Our results establish ${\mathcal{F}}_{\mathrm{SZM}}$ as a robust probe of localization-protected topological order and uncover distinctive topological features of infinite-randomness criticality. Unlike the clean Ising conformal field theory, where the finite critical value arises from a cancellation of power laws, the IRFP seems to exhibit an intrinsically stronger topological character. The edge-selective structure of the critical distributions may suggest a boundary manifestation of the average Kramers-Wannier duality symmetry at the IRFP.

Searching for and designing materials with ultralow thermal conductivity is vital for thermoelectrics and thermal management. Using first-principles calculations and a unified theory of thermal transport, we systematically investigate the lattice dynamics of orthorhombic $\mathrm{Be}{X}_2$ ($X$ = Cl, Br, I), accounting for anharmonic phonon renormalization (APR) and three- and four-phonon scattering. Due to their quasi-one-dimensional (quasi-1D) structure, these compounds exhibit pronounced thermal anisotropy. While the chain-direction ($a$ axis) lattice thermal conductivity (${\kappa }_L$) follows a standard $1/T$ scaling, the transverse ($b$ and $c$ axes) ${\kappa }_L$ shows anomalous nonmonotonic temperature dependence. This behavior originates from competition between particlelike phonon transport and wavelike coherent phonon transport. With increasing temperature, enhanced phonon scattering broadens the phonon linewidths, increases the spectral overlap between neighboring modes, and strengthens the off-diagonal coupling, thereby promoting the coherent transport channel, which eventually dominates ${\kappa }_L$. Four-phonon scattering substantially suppresses the particlelike contribution, particularly in compounds containing heavier halogens. APR hardens selected low-frequency acoustic modes and increases the corresponding direction-resolved phonon group velocities, but it also modifies the anharmonic scattering rates and phonon lifetimes through the temperature-dependent interatomic force constants. The synergistic effect of APR on ${\kappa }_L$ is therefore direction dependent and reflects competition between these harmonic and anharmonic factors. Overall, our findings elucidate the interplay between coherent phonon tunneling and higher-order anharmonicity in quasi-1D $\mathrm{Be}{X}_2$ and provide theoretical guidance for thermal management and the design of ultralow thermal conductivity materials.

${\mathrm{Mg}}_2{\mathrm{IrH}}_6$ is a metastable complex metal hydride with a predicted superconducting transition temperature as high as $170\mathrm{K}$ at ambient pressure. Following the synthesis of isomorphic, insulating ${\mathrm{Mg}}_2{\mathrm{IrH}}_5$ at low pressure, higher-pressure studies were conducted to investigate the phase behavior and compound formation in this system. X-ray diffraction and Raman spectroscopic measurements, combined with ab initio calculations, support the formation of cubic ${\mathrm{Mg}}_2{\mathrm{IrH}}_7$ above ca. 40 GPa. This phase may coexist with a related hexagonal hydride with an estimated composition near ${\mathrm{Mg}}_2{\mathrm{IrH}}_5$. Electrical transport measurements suggest that cubic ${\mathrm{Mg}}_2{\mathrm{IrH}}_7$ is insulating, in agreement with ab initio predictions, and persists during room-temperature decompression until $\sim 20\mathrm{GPa}$ before reverting back to cubic ${\mathrm{Mg}}_2{\mathrm{IrH}}_5$. The experimental results support ground-state structure predictions in the Mg-Ir-H system, and the formation of two nearly identical phases with surrounding compositions may open opportunities to access superconducting ${\mathrm{Mg}}_2{\mathrm{IrH}}_6$ through nonequilibrium processing pathways.

Charge transport in superconducting junctions at finite voltages is governed by Andreev reflections, including multiple Andreev reflections, which are processes that enable multiple charge transfer, a hallmark that shot noise can directly quantify. Since the effective charge extracted from shot-noise measurements varies with the transparency of the junction, systematic control of transparency is essential but experimentally challenging. Here, we present shot-noise scanning tunneling microscopy measurements enabled by a newly developed amplifier, allowing access to different transparency regimes. We perform shot-noise measurements on Pb(111) with tunable transparency at 2.2 K and observe that the shot noise evolves from a single-electron tunneling regime to multiple charge-transfer regimes as transparency increases. Our results are quantitatively consistent with theoretical simulations of Andreev reflections and multiple Andreev reflections for a single-channel system. These results establish junction transparency as the key parameter governing the evolution of charge transport and demonstrate that noise STM is a powerful platform for investigating microscopic charge transport mechanisms with controlled junction transparency at the atomic scale.

We investigate the robustness of topological phases in a Kitaev ladder composed of two coupled superconducting chains under the perturbing influence of a finite charge current. By introducing an effective Hamiltonian depending on the quasiparticle momentum induced by the current, we show that the two-mode topological phase, present in the isolated ladder, is fragile against a finite current flux. To characterize this behavior, we combine bulk topological invariants with real-space diagnostics, including the edge-edge quantum conditional mutual information $I_{ee}$, which provides an entanglement-based signature of topological order. We further distinguish the gapped class-D sectors from a current-induced gapless superconducting regime, which emerges when the upper Bogoliubov–de Gennes (BdG) branch crosses zero at generic momenta and the standard gapped topological invariant is no longer applicable. Our results provide an effective framework to describe how current injection and measurement processes can affect topological protection in superconducting nanostructures.

Confinement produces mesonic bound states, but their existence alone does not determine the statistical organization of the many-body spectrum. We investigate this connection in the spin-$\frac{1}{2}$ XXZ chain subject to a longitudinal staggered field, using symmetry-resolved exact diagonalization for spin chains of up to $N=22$ sites. As the exchange anisotropy is increased into the antiferromagnetic Ising regime, the finite-size spectra cross over from Gaussian-orthogonal-ensemble-like statistics to reduced level repulsion. This evolution occurs in both the zero-momentum and generic nonzero-momentum sectors examined. Direct measurements of the domain-wall-number operator and its eigenstate variance reveal increasingly sharp approximate domain-wall sectors, accompanied by banding of spin correlations and bipartite entanglement. Statistics within a selected domain-wall band further characterize the spectral organization beyond the full-sector gap-ratio analysis. We identify the one-meson branch and compare its energies and level spacings with established Airy and semiclassical descriptions and a finite-chain strong-anisotropy treatment, quantifying their accuracy and systematic deviations. These results connect the known confined two-spinon spectrum to the broader finite-anisotropy organization of many-body eigenstates and provide quantitative evidence for emergent domain-wall constraints in the full microscopic Hamiltonian.

This work introduces a theoretical framework based on the Kadanoff-Baym equations in spinor space to study ultrafast magnetization dynamics in itinerant ferromagnetic systems from first principles. By incorporating spin-orbit coupling into the ab initio Hamiltonian and generalizing the self-energies to include terms beyond the charge sector, I derive scattering integrals within the Markov approximation and quasiparticle renormalizations for electrons and phonons in the presence of spin-dependent effective interactions within a many-body perturbation theory approach. I explicitly discuss how magnons emerge in this framework, and derive, through suitable approximations, a closed and tractable set of equations for coupled electron, phonon, and magnon dynamics that can be solved from first principles. I discuss the equations of motion within a minimal ferromagnetic model, where the coupled equations are solved numerically. This approach allows one to treat coherent and incoherent magnetic dynamics on an equal footing, paving the way for a first-principles understanding of ultrafast magnetic dynamics and demagnetization, and opening the door to a truly predictive theory of femtomagnetism in periodic systems.

Light-induced superconducting-like states have been reported in several classes of correlated materials. From a theoretical point of view, the induction of $\eta$-pairing is a promising route to nonthermal superconductivity. Numerical studies of photo-doped Mott systems revealed $\eta$-pairing states with very high effective critical temperatures. These investigations were, however, restricted to particle–hole symmetric states in large-gap Mott insulators, while the experiments were performed on strongly correlated metallic systems without particle-hole symmetry. It is thus relevant to explore whether $\eta$-pairing also exists in non-particle–hole symmetric setups and in photo-excited metallic states. Here, we use steady-state nonequilibrium dynamical mean-field theory combined with a strong-coupling impurity solver up to third order to investigate this issue. We find that in the strongly correlated regime with a large Mott gap, and for low effective doublon and holon temperatures, $\eta$-pairing is robust against changes in the total filling and an imbalance in the doublon and holon density. An asymmetry in the effective doublon and holon temperatures can, however, strongly suppress the order parameter. In photo-doped metallic systems with a three-peak structure in the local density of states, $\eta$-pairing can be realized in setups with positive doublon and holon temperatures and a population inversion in the low-energy quasiparticle band.

The tunability and control of topological edge/surface states are crucial for the development of new device applications. In this work, by combining first-principles calculations and Wannier-based tight-binding methods, we show the emergence of quantum spin Hall phases in van der Waals heterostructures formed by stacking two trivial quintuple layers from the ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ family. We demonstrate the tunability of the edge states under interlayer strain and external electric field effects, suggesting the possibility of switching topological edge states on/off by external control. Additionally, the quantum spin Hall edge channels remain robust against interlayer twist, highlighting their stability against external perturbations. Our results provide an alternative way to create and manipulate two-dimensional topological phases in systems based on the ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ family, which can be valuable for practical applications, such as topological field-effect transistors and spintronic devices.

We use ab initio electronic-structure methods to investigate random matrix theory (RMT) universality in molecular electronic structure. Using single-reference electronic structure methods, including Hartree-Fock, configuration-interaction singles, density functional theory, and linear-response time-dependent density-functional theory, we compute single-particle orbital energies and many-electron excitations of several representative molecules (benzene, alanine, 1-phenylethylamine, methyloxirane, and helicene chains). For generic low-symmetry geometries, the unfolded spectra of these ab initio Hamiltonians exhibit Wigner-Dyson level statistics of the Gaussian orthogonal ensemble (GOE). For extended helicene chains we explicitly restrict to bound valence excitations below the ionization threshold and still observe signatures of GOE, indicating that the RMT universality may also emerge for physical states of direct relevance to real molecules. We further explore the electric and magnetic field dependence of the molecular electronic spectra. The variance of electric polarizability (level curvature, $K$) is predicted to be nonanalytic in the magnetic field which serves as an infrared cutoff, $\langle K^2\rangle \propto ln(1/|B\left|\right)$. We observe a transition to the Gaussian unitary ensemble by increasing the magnetic fields, although it occurs only at magnetic fields far beyond experimentally accessible scales. Our results indicate that random matrix universality provides a general framework for organizing ab initio predictions of interacting electron spectra in complex systems.

We explore the effects of nonmagnetic impurities (vacancy disorder) on the quantum paramagnetic phases stabilized by SU($N$) designer Hamiltonians on bipartite lattices. Using the results of our quantum Monte Carlo simulations, we demonstrate that isolated vacancies seed emergent localized SU($N$) moments (analogs of spin moments for SU(2)) in their vicinity when the low-temperature state has valence bond solid order. Indeed, our quantum Monte Carlo results for the low-temperature susceptibility in such regimes show clear evidence of the vacancy-induced Curie tails associated with these emergent moments, and our zero-temperature projector Monte Carlo results on the ground-state wave function in the valence bond basis provide additional evidence in support of this picture. Further, for such designer Hamiltonians on the Lieb lattice with two additional sites on each bond of a square lattice, we identify a low-temperature spin-liquidlike regime with no sign of spin or valence bond order. This liquidlike regime serves as a testbed for validating a recently developed argument concerning the effects of vacancy disorder in such low-temperature regimes. Consistent with this argument, we find that isolated vacancies do not seed emergent local moments in such spin liquids. Instead, in the presence of vacancy disorder, emergent local moments are associated with the presence of monomers in maximum-density dimer packings of the corresponding diluted lattice.

We report the study of plasmon-exciton coupling in nanoparticles with a metal core and an outer J-aggregate shell. Our theoretical consideration shows that in many cases of practical importance, the use of the conventional model of two coupled oscillators containing a single coupling constant $g$ is oversimplified for a reliable description of plexcitonic (plasmon-exciton) coupling effects in such systems. Therefore, one needs to develop a more justified approach for accurate evaluation of the plexcitonic coupling efficiency. Here we demonstrate that for core-shell nanospheres, two plexcitonic coupling constants $g_{+}$ and $g_{-}$ emerge naturally in our theory because of the electromagnetic coupling of the dipolar localized surface plasmon-polariton with two excitonic shell resonances. Such resonances are caused by the splitting of a J-aggregate peak owing to the presence of inner and outer boundaries of the organic shell. Our approach is rigorously justified for hybrid core-shell nanoparticles of spherical shape, and it is more suitable for a reliable description of light extinction spectra and for quantitative determination of plexcitonic coupling efficiency than the model of two coupled oscillators. We derive simple analytical expressions for the introduced coupling constants, $g_{+}$ and $g_{-}$. Our calculations for various plexcitonic nanoparticles with a gold or silver core and an isotropic J-aggregate shell are in good agreement with the extinction spectra obtained using exact equations. This work broadens the understanding of the physical phenomena caused by plasmon-exciton coupling and provides a means for the correct determination of its efficiency.

Longitudinal nonreciprocal charge transport is usually associated with broken time-reversal symmetry, either from magnetic order or an external magnetic field. Here, we show that it can also arise in nonmagnetic conductors preserving time-reversal symmetry through disorder-induced asymmetric scattering. Within a semiclassical Boltzmann theory, skew-scattering and side-jump processes generate a finite longitudinal current quadratic in the electric field. Our symmetry analysis identifies 42 point groups that allow this longitudinal nonreciprocal response. As a concrete example, gated Bernal-stacked bilayer graphene exhibits a gate-tunable nonreciprocal response, with a clear enhancement near its van Hove singularities. These results identify disorder-driven asymmetric scattering as a route to bulk longitudinal nonreciprocal charge transport in crystalline conductors.

We study an infinite-range coupled electronic-pseudospin and nuclear-spin model for ferroquadrupolar and nuclear-spin ordering in ${\mathrm{TmVO}}_4$ in external magnetic and strain fields. This material is an experimental realization of a transverse-field Ising model, where the Ising degree of freedom is quadrupolar and nonmagnetic, but a transverse component is magnetic and couples both to external magnetic fields and to the nuclear spins via a hyperfine coupling. At zero external magnetic field, the electronic and nuclear degrees of freedom undergo well-separated two-stage ordering, accompanied by the release of their respective entropies. A transverse magnetic field polarizes the electronic orbital moments and, via the hyperfine coupling, the nuclear spins. The quadrupolar ordering temperature is gradually reduced to zero. However, the nuclear transition is replaced by a crossover at nonzero magnetic field. Quantum fluctuations are enhanced near the phase transitions and lead to peaks in the magnetic susceptibility. The spectral functions reveal a softening of a low-energy mode near the quantum critical point, consistent with the closing of the excitation gap and its reopening in the disordered phase. These features provide direct dynamical signatures of the field-driven quantum critical phenomena.