Exciton dissociation plays a crucial role in the performance of optoelectronic devices based on two-dimensional (2D) transition metal dichalcogenides (TMDs). In this work, we investigate the effect of an in-plane electric field on the exciton resonance states in ${\mathrm{MX}}_2$ (M = Mo, W; X = S, Se) monolayers and few layers using the complex coordinate rotation method and the Lagrange-Laguerre polynomial expansion of the wave function. This technique enables accurate computation of both ground and excited excitonic states across a wide range of electric field strengths, overcoming limitations of previous perturbative approaches. Our calculations reveal that an electric field effectively dissociates excitons, with excited states being more easily dissociated than the ground state. The critical field for exciton dissociation is found to be smaller in ${\mathrm{WX}}_2$ monolayers compared to ${\mathrm{MoX}}_2$ monolayers due to the smaller exciton reduced mass. Furthermore, the presence of a dielectric substrate and an increase in the number of ${\mathrm{MX}}_2$ layers enhance the exciton susceptibility to the electric field, lowering the critical field for dissociation. The dependence of exciton properties on the number of ${\mathrm{MX}}_2$ layers can be well described by power functions. These findings provide valuable insights for the design and optimization of high-performance optoelectronic devices based on 2D TMDs.

The identification of atomic species on ${\mathrm{CaF}}_2\left(111\right)$ surfaces in noncontact atomic force microscopy (NC-AFM) measurements is revisited by a combinatorial qualitative analysis of images taken at different tip-sample distances. Based on the surface symmetry and without further knowledge of the tip state, a total of four principal contrast modes are predicted. All of these contrast modes are found in experiments and can be explained by a tip-surface interaction model based on electrostatic interactions in combination with Pauli repulsion. It is demonstrated that a set of two images taken at appropriate tip-sample distances is sufficient to unambiguously identify the three sublattices of the ${\mathrm{CaF}}_2\left(111\right)$ surface as well as the polarity of the tip-terminating cluster yielding atomic contrast.

The anti-Stoner excitations are a spin flips in which an electron is effectively promoted from a minority to a majority spin state, i.e., complementary to Stoner excitations and spin waves. Since their spectral power is negligible in strong itinerant ferromagnets and they are entirely absent in the ferromagnetic Heisenberg model, their properties and role in correlating electrons have scarcely been investigated. However, they are present in weak ferromagnets, fcc Ni being a prominent example. Both types of spin flips (down-to-up and up-to-down) must be treated equally in systems with degenerate spin-up and spin-down bands, particularly in antiferromagnets, for which we choose CrSb as a model system. For these two materials, we evaluate the strength of the effective interaction between the quasiparticles and the gas of virtual spin-flip excitations. To this end, we compute the corresponding self-energy taking advantage of our efficient ab initio numerical scheme [Phys. Rev. B 107, 134410 (2023)]. In Ni, we find that the band-structure renormalization caused by the anti-Stoner processes is weaker than that caused by Stoner-type magnons in the majority spin channel, but the two become comparable for minority spin carriers. The effect can be traced back primarily to the spectral strength of the respective spin excitations and the densities of the final available quasiparticle states in the scattering process. In the antiferromagnet, the situation is more complex and we observe that the electron-magnon interaction is sensitive not only to these densities of states but also critically to the spatial shapes of the coupling magnonic modes.

Symmetry-protected edge states serve as direct evidence of nontrivial electronic topology in atomically thin materials. Finding these states in experimentally realizable single-phase materials presents a substantial challenge for their use in fundamental studies and developing functional nanoscale devices. Here, we show the presence of robust edge states in phosphorene and group-Va monolayers with puckered lattice structures. By carefully analyzing the symmetry of the atomic sites and edge mode properties, we demonstrate that these atomically thin monolayers realize recently introduced obstructed atomic insulator states with partially occupied edge modes. The obstructed edge modes attain a Rashba-type spin splitting with Rashba parameter ($\alpha$) of 1.52 eV Å for arsenene. Under strain or doping effects, these obstructed insulators transition to a phase with substantial spin-Berry curvature, yielding a double quantum spin Hall state with a spin Hall conductivity $\approx 4\frac{e^2}{h}$. The experimental availability of phosphorene and other group-Va monolayers could enable verification of obstructed atomic states and enhanced spin-Berry curvature effects discussed in this study, offering the potential for applications in topological electronic and spintronic devices.

We investigated the behavior of fractional quantum Hall (FQH) states in a two-dimensional electron system with layer thickness and an in-plane magnetic field. Our comparisons across various filling factors within the first Landau level revealed a crucial observation. A slight in-plane magnetic field specifically enhances the nematic order of the $\nu =7/3$ FQH state. For this particular filling, through calculating the energy gap, the Ising nematic order parameter, the pair-correlation function, and the static structure factor, we observed that as the in-plane magnetic field increases, the system started from the isotropic FQH (IFQH) state, first enters into an anisotropic FQH (AFQH) phase without closing the spectrum gap, then the FQH nematic (FQHN) phase after neutral gap closing. The system eventually enters a gapless one-dimensional charge density wave (CDW) phase for a large in-plane field. We thus provide a full phase diagram of the $\nu =7/3$ state in a tilted magnetic field, demonstrating the existence of the FQHN, which aligns with recent resonant inelastic light scattering experimental observations.

We study a model of spinless fermions on the honeycomb lattice with nearest-neighbor exclusion and extended repulsive interactions that exhibits “lattice supersymmetry” [P. Fendley et al., Phys. Rev. Lett. 90, 120402 (2003)]. Using a combination of exact diagonalization of large ($N\le 56$ site) systems, mean-field numerics, and symmetry analysis, we establish a rich phase structure as a function of fermion density, that includes non-Fermi-liquid behavior, resonating charge stripes, domain-wall and bubble physics, and identify a finite range of fillings with extensive ground-state degeneracy and both gapped and gapless spectra. We comment on the stability of our results to relaxing the stringent requirements for supersymmetry, and on their possible broader relevance to systems of strongly correlated electrons with extended repulsive interactions.

We demonstrate that a disordered Fermi system with density-density interaction can undergo a metal-dielectric phase transition, which depends on the relationship between the real physical dimensionality $d$ and the degree of disorder. The disorder is modeled by a fractional Laplacian with Lévy index $\alpha$ in place of the ordinary one in the single-particle kinetic energy operator. Our studies of various benchmark regimes marked by an effective system dimension $\gamma =(d-\alpha )/\alpha$ show a pattern of dimensional flow of the system's density of states (DOS) at the Fermi surface. This pattern describes the continuous change of the DOS as $\gamma$ varies. Additionally, by including the extended Coulomb interaction with a general power law $r^{-\beta }$ (where $\beta \ge 0$) into the model, we observe the effect of dimensional transmutation, in which the Coulomb exponent $\beta$ becomes the effective spatial dimension. As our combined parameter $\gamma$ permits to manipulate the properties of above metal-dielectric phase transition, our findings can be used to improve functionality of the transition metal dichalcogenide channel transistors and other nanoelectronic devices.

Phonon vibration excitation is an effective approach to enhance photoelectric conversion efficiency of $g\text{−}{\mathrm{C}}_3{\mathrm{N}}_4$-based heterostructures, yet the influencing mechanism on interlayer transfer of photogenerated charges remains unclear. Herein, we show first-principles evidence of using $g\text{−}{\mathrm{C}}_3{\mathrm{N}}_4/$ transition metal dichalcogenide ($\mathrm{MoT}{\mathrm{e}}_2$ and $\mathrm{WT}{\mathrm{e}}_2$) heterostructures to achieve ultrafast interlayer transfer of photogenerated electrons and holes at the timescales of 4 ps and 200 fs, respectively. Our findings reveal that the fast transfers of photogenerated electrons and holes are both promoted by a nonadiabatic (NA) mechanism, driven via the coupling of donor and acceptor electronic states with the same phonon state. Notably, this coupling in the valence bands is significantly stronger than that in the conduction bands, which enhances interface atom motion, reduces interface distance, and strengthens wave-function overlap of spatial localized electronic states, thereby synergistically producing much faster hole transfer. Moreover, the hole transfer is also enhanced by an adiabatic (AD) mechanism through phonon-induced crossing of valence bands. Our study identifies that the synergistic effects of phonon-induced NA and AD mechanisms play a key role in interlayer transfer of photogenerated charges within $g\text{−}{\mathrm{C}}_3{\mathrm{N}}_4$-based heterostructures.

Twisted bilayer structures have emerged as a fascinating arena in condensed matter thanks to their highly tunable physics. The role of spin-orbit coupling (SOC) in twisted bilayers has gained increasing attention due to its potential for spintronics. Thus, it is appealing to propose new materials for constructing twisted bilayers with substantial SOC. In this work, the intriguing effects induced by twisting two layers of two-dimensional bismuthene are unraveled from large-scale first-principles calculations. We show that spin-orbit coupling significantly affects the electronic properties of twisted bilayer bismuthene, even more than in its untwisted counterpart. We carefully investigate how the interplay between the SOC and the twist angle impacts the band structure and spin textures of twisted bilayer bismuthene. We find that the twist angle can be deemed a control knob to switch from a small-gap semiconductor to a metallic behavior. Most crucially, the accurate analysis of the energy bands close to Fermi energy reveals a twist-tunable splitting in the mexican-hat shape of the bands that can otherwise be obtained only by applying enormous electric fields. Our predictions provide insight into innovative bismuth-based technologies for future spintronic devices.

Recently, the application of isotope engineering to design and optimize near-field radiative thermal diodes based on polar materials has emerged as an appealing and promising technique. Besides the isotope effect, the lattice thermal expansion in those polar materials with light atoms impacts appreciably their phonon and optical properties. In this work, we present a strategy for designing efficient thermal diodes through the synergy between isotope engineering and lattice expansion in light polar materials. The isotope-induced phonon frequency shift as well as the phonon softening with temperature thus give rise to match and mismatch of surface phonon polaritons (SPhPs) resonant frequency under forward and reverse temperature bias, respectively. Using cubic boron nitride (cBN) as a material platform, we obtain its dielectric function from first-principles calculation, including the four-phonon scattering and phonon frequency shift. This computational design allows us to achieve an ultrahigh thermal rectification ratio of 7.01 at a 10 nm gap, which is 75% higher than that with only isotope engineering. This study thus paves a way for effective design of radiative thermal diodes that may promote the thermal management of electronics and optoelectronics.

We study phase transitions driven by structural disorder in noncrystalline topological insulators. We introduce a procedural generation algorithm, the Perlin noise, typically used in computer graphics, to incorporate disorder to a two-dimensional lattice, allowing for a continuous interpolation between a pristine and a random lattice system, going through all different intermediate structural regimes, such as the paracrystalline and amorphous phases. We define a two-band model, including intraorbital and interorbital mixings, on the structures generated by the algorithm and we find a sequence of structure-driven topological phase transitions characterized by changes in the topological Bott index at which the insulating gap dynamically closes while evolving from the Bragg planes of the Brillouin zone towards the center. We interpret our results within the framework of Hosemann's paracrystal theory, in which distortion is included in the lattice structure factor and renormalizes the band-splitting parameter.

Understanding complex quantum dynamics in realistic materials requires insight into the underlying correlations that dominate the interactions between the participating particles. Due to the wealth of information involved in these processes, the application of artificial intelligence (AI) methods is compelling. However, unsupervised data-driven approaches typically focus on identifying maximum variations in data, rather than considering the correlations between them. Here, we present an approach that recognizes correlation patterns to explore convoluted dynamical processes. Our scheme uses singular value decomposition to extract dynamical features, unveiling the internal temporal-spatial interrelations that generate the dynamical mechanisms. We apply our approach to study light-induced wave-packet propagation in organic crystals, of interest for applications in material-based quantum computing and quantum information science. We show how transformation from the input momentum and time coordinates onto a new correlation-induced coordinate space allows direct recognition of the relaxation and dephasing components dominating the dynamics and we demonstrate their dependence on the initial pulse shape. A tensor product state composed of a linear combination of singular vectors is suggested as a pathway to reproduce the information required for further explainability of these mechanisms. Our method offers a route for elucidating complex dynamical processes using unsupervised AI-based analysis in multicomponent systems.

The nature of the charge carriers in high-$T_c$ cuprates is an essential issue to reveal their novel physical properties and the mechanism of their superconductivity. However, the experimental probes and the theoretical analysis have been mostly restricted to the linear responses. On the other hand, recent observations of Rashba-type spin-orbit coupling on the surface of high-$T_c$ cuprates imply the possible nonlinear and nonreciprocal transport phenomena under in-plane magnetic fields. In this paper, we study the nonreciprocal transport properties on the surface of cuprates by employing a $U\left(1\right)$ gauge theory framework, where the electrons are considered to be fractionalized. Our investigation highlights the intricate variations in nonreciprocal transport with respect to temperatures and dopings. First, it reveals contrasting behavior of nonreciprocity in each normal phase. Second, it discerns the tendencies between underdoped and overdoped superconducting states and their paraconductivity. The complex behaviors of nonreciprocal transport originate from the spinful and spinless nature of the charge carriers and their kinetic energy scales. These findings pave a new avenue to explore the electronic states in high-$T_c$ cuprates in terms of nonreciprocal transport phenomena.

To explore the influence of quantum-geometric effects on the Ginzburg-Landau coherence length in a dilute flat-band superconductor, we adopt a BCS-BEC crossover approach to the multiband pyrochlore-Hubbard model near the critical temperature for superconductivity. Our self-consistent formulation for this three-dimensional lattice benchmarks very well against the so-called zero-temperature coherence length, demonstrating the monotonic decay of the coherence length to zero as the interaction strength increases. Additionally, we show that the effective mass of the many-body bound states (i.e., Cooper pairs) is nearly identical to that of the lowest-lying two-body bound states in the dilute flat-band limit.

We study magnetic properties of ${\mathrm{CrO}}_2$ within the density functional theory plus dynamical mean-field theory (DFT+DMFT) approach in the paramagnetic phase. We consider the 3-orbital (per Cr site) model, containing only $t_{2g}$ states, the 5-orbital model, including all $d$-states, as well as the model including also the oxygen $p$ states. Using the recently proposed approach of calculation of exchange interactions in paramagnetic phase, we extract exchange interaction parameters and magnon dispersions for these models. While the magnon dispersion in the 3-orbital model possesses negative branches in accordance with previous studies in ferromagnetic phase, this drawback is removed in the 5-orbital model. The model, including oxygen states (with purely local interaction at chromium sites), overestimates the exchange interactions and spin-wave stiffness. While this overestimation is partly corrected by including nonlocal interaction between chromium and oxygen states within the static mean-field approximation, the 5-orbital model appears as most adequate for describing magnetic properties of ${\mathrm{CrO}}_2$ with local Coulomb interaction. The possibility of describing magnetic properties of this material starting from paramagnetic phase points to the correspondence of magnetic properties in this phase and ferromagnetic phase, as well as to the important contributions of double exchange in paramagnetic phase of ${\mathrm{CrO}}_2$.

Topological theory predicts the necessary conditions for robust dimensional reduction in a host of quantum and classical systems. Models have recently been proposed for stochastic systems which describe many biological and chemical phenomena. However, general theoretical principles are lacking for this class of systems, exemplified by the breakdown of the celebrated bulk-edge correspondence. We prove that contrary to topological phases in quantum and many classical systems, stochastic systems require nonreciprocal (or non-Hermitian) transitions for robust edge responses, which holds across all dimensions and geometries. We propose a novel explanation of hybridization that destroys edge responses in reciprocal (Hermitian) stochastic systems. Further, we show that stochastic steady states grow dramatically with nonreciprocity, in contrast to their quantum counterparts which plateaus. We analyze the resulting theoretical and physical consequences and how nonreciprocity mitigates the effects of hybridization towards robust edge states in equilibrium and nonequilibrium steady states. These results establish the crucial role of nonreciprocal interactions for responses that are robust to random perturbations in active and living matter.

We study the interplay between an on-site Hubbard repulsion and quasiperiodic potential in one-dimensional fermion chains using the density matrix renormalization group. We find that, at half filling, the quasiperiodic potential can destroy the Mott gap, leading to a metallic Luttinger liquid phase between the gapped Mott insulator at strong repulsion and the localized gapless Aubry-André insulator at strong quasiperiodic potential. Away from half filling, the metallic phase of the interacting model persists to larger critical strengths of the potential than in the noninteracting case, suggesting interaction-stabilized delocalization at finite doping. We characterize the Luttinger liquid through its charge and spin correlations, structure factors, and entanglement entropy.

Quasi-one-dimensional (1D) materials provide a unique platform for understanding the importance and influence of extended interactions on the physics of strongly correlated systems due to their relative structural simplicity and the existence of powerful theoretical tools well adapted to one spatial dimension. Recently, this was highlighted by anomalous observations in the single-particle spectral function $A(q,\omega )$ of 1D cuprate chain compounds, measured by angle-resolved photoemission spectroscopy (ARPES), which were explained by the presence of a long-range attractive interaction. Such an extended interaction should leave its fingerprints on other observables, notably the dynamical spin structure factor $S(q,\omega )$, measured by neutron scattering or resonant inelastic x-ray scattering. Starting from a simple Hubbard Hamiltonian in 1D and using time-dependent density matrix renormalization group methods, we show that the presence of long-range attractive coupling, directly through an instantaneous Coulomb interaction $V$ or retarded electron-phonon (el-ph) coupling, can introduce significant spectral weight redistribution in $S(q,\omega )$ across a wide range of doping. This underscores the significant impact that extended interactions can have on dynamical correlations among particles, and the importance of properly incorporating this influence in modeling. Our results demonstrate that $S(q,\omega )$ can provide a sensitive experimental constraint, which complements ARPES measurements, in identifying key interactions in 1D cuprates, beyond the standard Hubbard model.

The Grassmann time-evolving matrix product operator (GTEMPO) method has proven to be an accurate and efficient numerical method for the real-time dynamics of quantum impurity problems. However, its application for imaginary-time calculations is much less competitive than well-established methods such as the continuous-time quantum Monte Carlo (CTQMC). In this work, we unleash the full power of GTEMPO for zero-temperature imaginary-time calculations: The multitime impurity state is time-translationally invariant with infinite boundary conditions; therefore, it can be represented as an infinite Grassmann matrix product state (GMPS) with a nontrivial unit cell in a single time step, instead of an open boundary GMPS spanning the whole imaginary-time axis. We devise a very efficient infinite GTEMPO algorithm targeted at zero-temperature equilibrium quantum impurity problems, which is known to be a hard regime for quantum Monte Carlo methods. To demonstrate the performance of our method, we benchmark it against exact solutions in the noninteracting limit and against CTQMC calculations in the Anderson impurity models with up to two orbitals, where we show that the required bond dimension of the infinite GMPS is much smaller than its finite-temperature counterpart.