We study the scaling of the entanglement entropy in different classes of one-dimensional fermionic quasiperiodic systems with and without pairing, focusing on multifractal critical points/phases. We find that the entanglement entropy scales logarithmically with the subsystem size $N_A$ with a proportionality coefficient $\mathcal{C}$, as in homogeneous critical points, apart from possible additional small oscillations. In the absence of pairing, we find that the entanglement entropy coefficient $\mathcal{C}$ is nonuniversal and depends significantly and nontrivially both on the model parameters and electron filling, in multifractal critical points. In some of these points, $\mathcal{C}$ can take values close to the homogeneous (or ballistic) system, although it typically takes smaller values. We find a close relation between the behavior of the entanglement entropy and the small-$q$ (long-wavelength) dependence of the momentum structure factor $\mathcal{S}\left(q\right)$. $\mathcal{S}\left(q\right)$ increases linearly with $q$ as in the homogeneous case, with a slope that grows with $\mathcal{C}$. In the presence of pairing, we find that even the addition of small anomalous terms affects very significantly the scaling of the entanglement entropy compared to the unpaired case. In particular, we focused on topological phase transitions for which the gap closes with either extended or critical multifractal states. In the former case, the scaling of the entanglement entropy mirrors the behavior observed at the critical points of the homogeneous Kitaev chain, while in the latter, it shows only slight deviations arising at small length scales. In contrast with the unpaired case, we always observe $\mathcal{C}\approx 1/6$ for different critical points, the known value for the homogeneous Kitaev chain with periodic boundary conditions.

Effective heat dissipation is critical for the performance and longevity of electronic devices. This study delves into the intricacies of thermal boundary conductance (TBC) between multilayer graphene and silicon, scrutinizing its correlation with graphene thickness. Employing a combination of the no-transducer time-domain thermal reflection technique and nonequilibrium molecular dynamics simulations with empirical and machine-learning based potentials, we discover an intriguing behavior: TBC initially increases with graphene thickness, but it eventually converges, suggesting that this phenomenon originates from the transition of the phonon transport from the ballistic to the diffusive regime in multilayer graphene. It is further demonstrated that a graphene-${\mathrm{MoS}}_2$ heterostructure exhibits a thickness-independent TBC behavior due to the strong phonon localization across the entire frequency range. The present study emphasizes the significance of incorporating phonon transport regimes in the design and optimization of thermal interfaces, laying the groundwork for innovative strategies to enhance heat dissipation in electronic devices.

We examine a non-Hermitian (NH) tight-binding system comprising two orbitals per unit cell and their electrical circuit analogs. We distinguish the $\mathcal{PT}$-symmetric and non-$\mathcal{PT}$-symmetric cases characterized by nonreciprocal nearest-neighbor couplings and on-site gain and loss terms, respectively. The localization of the edge modes or the emergence of the topological properties is determined via the maximum inverse participation ratio, which has distinct dependences on the parameters that define the Hamiltonian. None of the above scenarios exhibit the non-Hermitian skin effect. We investigate the boundary modes corresponding to the topological phases in a suitably designed electrical circuit by analyzing the two-port impedance and retrieve the admittance band structure of the circuit by imposing periodic boundary conditions. The obtained results are benchmarked against the Hermitian version of the two-orbital model to compare with and differentiate from those obtained for the NH variants.

We investigate the behavior of entanglement between a single fermionic level and a fermionic bath in three distinct thermodynamic regimes. First, in thermal equilibrium, we analyze the dependence of entanglement on the considered statistical ensemble: for the grand canonical state, it is generated only for a sufficiently strong system-bath coupling, whereas it is present for arbitrarily weak couplings for the canonical state with a fixed particle number. The threshold coupling strength at which entanglement appears is shown to strongly depend on the bath bandwidth. Second, we consider the relaxation to equilibrium. In this case a transient entanglement in a certain time interval can be observed even in the weak-coupling regime, when the reduced dynamics and thermodynamics of the system can be well described by an effectively classical and Markovian master equation for the state populations. At strong-coupling strengths, entanglement is preserved for long times and converges to its equilibrium value. Finally, in voltage-driven junctions, a steady-state entanglement is generated for arbitrarily weak system-bath couplings at a certain threshold voltage. It is enhanced in the strong-coupling regime, and it is reduced by either the particle-hole or the tunnel coupling asymmetry.

In this paper, we provide a comprehensive overview of the microwave-induced manipulation of electronic spin states in negatively charged group-IV color centers in diamond with a particular emphasis on the influence of strain. Central to our investigation is the consideration of the full vectorial attributes of the magnetic fields involved, which are a $dc$ field for lifting the degeneracy of the spin levels and an $ac$ field for microwave control between two spin levels. We observe an intricate interdependence between their spatial orientations, the externally applied strain, and the resultant efficacy in spin-state control. In most studies to date the $ac$ and $dc$ magnetic field orientations have been insufficiently addressed, which has led to the conclusion that strain is indispensable for the effective microwave control of heavier group-IV vacancies, such as tin- and lead-vacancy color centers. In contrast, we find that the alignment of the $dc$ magnetic field orthogonal to the symmetry axis and the $ac$ field parallel to it can make the application of strain obsolete for effective spin manipulation. Furthermore, we explore the implications of this field configuration on the spin's optical initialization, readout, and gate fidelities.

We theoretically study scanning gate microscopy (SGM) of electron and hole trajectories in a quantum point contact (QPC) embedded in a normal-superconductor (NS) junction. At zero voltage bias, the electrons and holes transported through the QPC form angular lobes and are subject to self-interference, which marks the SGM conductance maps with interference fringes analogously as in normal systems. We predict that for an NS junction at nonzero bias, a beating pattern is to occur in the conductance probed with the use of the SGM technique owing to a mismatch of the Fermi wave vectors of electrons and holes. Moreover, the SGM technique exposes a pronounced disturbance in the angular conductance pattern, as the retroreflected hole does not retrace the electron path due to wave vector difference.

Two-dimensional (2D) semiconducting and metallic transition metal dichalcogenides (TMDs) have attracted significant attention for their promising applications in a variety of fields. Experimental observations of large exciton binding energies and nonhydrogenic Rydberg series in 2D semiconducting TMDs, along with deviations in plasmon dispersion in 2D metallic TMDs, suggest the presence of a nonconventional screening of the Coulomb interaction. The experimentally observed Mott insulating state in the charge density wave (CDW) reconstructed lattice of TMDs containing $4d$ and $5d$ elements further confirms the presence of strong Coulomb interactions in these systems. In this study, we use first-principles electronic structure calculations and constrained random-phase approximation to calculate the Coulomb interaction parameters (partially screened $U$ and fully screened $W$) between localized $d$ electrons in 2D TMDs. We specifically explore materials represented by the formula ${MX}_2$ $(M=\mathrm{Nb}, \mathrm{Ta}, \mathrm{Mo}, \mathrm{W}; X=\mathrm{S}, \mathrm{Se}, \mathrm{Te})$ and consider three different phases $(1H, 1T, \text{and} 1T^{\prime })$. Our results show that the short-range interactions are strongly screened in all three phases, whereas the long-range interactions remain significant even in metallic systems. This nonconventional screening provides a compelling explanation for the deviations observed in the usual hydrogenic Rydberg series and conventional plasmon dispersion in 2D semiconducting and metallic TMDs, respectively. Our calculations yield on-site Coulomb interaction parameters $U$ within the ranges of 0.8–2.5, 0.8–1.9, and 0.9–2.4 eV for the $1H$, $1T$, and $1T^{\prime }$ structures, respectively. These values depend on the specific chalcogen X, the number of $d$ electrons, and the correlated subspace. Using the calculated $U$ parameters for the undistorted $1T$ structure, we extract the on-site effective $U_{00}^{\mathrm{eff}}$ and nearest-neighbor $U_{01}^{\mathrm{eff}}$ Coulomb interaction parameters for reconstructed commensurate CDW $\mathrm{Nb}{X}_2$ and $\mathrm{Ta}{X}_2$ compounds. Furthermore, our findings indicate a substantially high ratio of on-site effective Coulomb interaction to bandwidth $(U_{00}^{\mathrm{eff}}/W_b\gg 1)$ in CDW TMDs, providing robust evidence for the experimentally observed strongly correlated Mott phase. This work sheds light on the nonconventional screening of Coulomb interactions in 2D TMDs, offering valuable insights into their electronic properties and potential applications in emerging technologies. It advances our fundamental understanding of these materials and holds promise for their use in various applications.

${\mathrm{PbTaS}}_2$ is a metal intercalated, layered transition metal dichalcogenide compound which has recently been predicted to be a potential topological superconductor (TSC), with a superconducting transition temperature of 2.6 K. Besides the strong interest in this class of materials, because of their high potential in quantum-computing applications, many aspects of their phenomenology are still undisclosed. Combining angle-resolved photoemission spectroscopy measurements and density functional theory calculations, we have studied the electronic properties of the centrosymmetric type-II superconductor ${\mathrm{PbTaS}}_2$ single crystals in the metallic phase, showing the presence of surface states, originated from the Pb-terminated surface, and of topological nodal lines, formed by the crossing of Ta $d_{xy}/d_{x^2-y^2}$ and Pb $p_x/p_y$ orbitals. The evidence of surface states connecting the nodal lines, as already discovered on structurally similar materials to be typical features of nodal-line semimetal-like TSCs, makes ${\mathrm{PbTaS}}_2$ a good candidate for exploring topological superconductivity.

The generation of higher-order harmonic radiation originating from the interaction of intense laser pulses with matter is typically described semiclassically: While the electronic structure and dynamics of matter is described quantum mechanically, the intense light field is described classically—and accordingly the generated harmonic radiation. However, pioneering experiments on quantum optical properties of high-order harmonic generation (HHG) in atomic gases from the group of P. Tzallas [I. Gonoskov et al., Sci. Rep. 6, 32821 (2016) and N. Tsatrafyllis et al., Nat. Commun. 8, 15170 (2017)], and theoretical investigations from the group of M. Lewenstein [M. Lewenstein et al., Nat. Phys. 17, 1104 (2021) and P. Stammer et al., Phys. Rev. Lett. 128, 123603 (2022)] have impressively demonstrated that light's quantum properties are observable in the strong-field realm. In this paper, we develop a quantum optical description of HHG in a bulk semiconductor originating from the nonlinear Bloch current. This mechanism of HHG, known as the intraband current, constitutes the major contribution to the emission spectrum for harmonic with energies of quanta roughly below the bandgap. Under certain approximations, employing a quantum description of both light and matter, we obtain analytical solutions, which allow us to analyze the classical and quantum optical characteristics of the fundamental mode of light and the harmonic modes. We find intricate but sufficiently mild modifications of the photon statistics of the fundamental mode and coherent displacements depending on the parameters of the driving laser field. Similar to high-harmonic generation in atoms, the fundamental and emitted harmonic field modes are entangled. Moreover, our analytical model predicts parameter ranges where these quantum optical properties will be most pronounced, allowing protocols for quantum information processing with high photon numbers over a large range of frequencies.

We investigate the magnetotransport of topological Dirac semimetals (DSMs) while taking into account the Lifshitz transition of the Fermi arc surface states. We demonstrate that a bulk momentum-dependent gap term, which is usually neglected in the study of bulk energy-band topology, can cause the Lifshitz transition by developing an additional Dirac cone on the surface to prevent the Fermi arcs from connecting with the bulk Dirac points. As a result, Weyl orbits can be turned off by the surface Dirac cone without destroying the bulk Dirac points. In response to the surface Lifshitz transition, the Weyl-orbit mechanism for the three-dimensional (3D) quantum Hall effect (QHE) in topological DSMs will break down. The resulting quantized Hall plateaus can be thickness dependent, similar to those based on Weyl orbits but their widths and quantized values become irregular. Accordingly, we propose that apart from bulk Weyl nodes and Fermi arcs, surface Lifshitz transitions are also crucial for realizing stable Weyl orbits and 3D QHE in real materials.

Bulk transition metal dichalcogenides (TMDs) have found widespread applications on nanophotonics, condensed matter physics, and quantum optics, due to their high refractive index and stable excitonic response at room temperature. In this paper, based on the finite-element method simulations, we demonstrate that the high refractive index enables the fabrication of bulk $\mathrm{W}{\mathrm{S}}_2$ into high-quality-factor metasurfaces that support chiral quasibound states in the continuum (Q-BICs). Interestingly, the Q-BIC resonance can in turn hybridize with excitons in the $\mathrm{W}{\mathrm{S}}_2$ metasurface itself. The self-hybridized exciton-polaritons, induced by the strong coupling between a Q-BIC and excitons, exhibit a typical anticrossing behavior with the Rabi splitting up to 136.5 meV. Such remarkable anticrossing behavior is also well elucidated by the coupled oscillator model. Intriguingly, we numerically verify that the self-hybridized exciton-polaritons are photonic spin-controlled, attributed to the chiral Q-BIC with the circular dichroism approaching 0.91. Therefore, we can control the exciton-photon interaction by simply changing the helicity of incident light. We believe that the outstanding self-hybridized exciton-polaritons in a $\mathrm{W}{\mathrm{S}}_2$ metasurface itself, without external microcavities, could pave the way for large-scale, low-cost integrated polaritonic devices at room temperature. Additionally, the chiral Q-BIC will enrich the toolbox for engineering exciton-photon interactions in bulk TMDs and other semiconductors. The photonic spin-controlled self-hybridized exciton-polaritons would find utility in ultrafast all-optical switches, modulators, chiral light-emitting devices, and valleytronic devices.

Floquet topological insulators have been widely investigated in lower-dimensional systems. However, Floquet topological insulators induced by time-periodic driving in higher-dimensional systems remain unexplored. In this work, we study the effects of time-periodic driving in a four-dimensional (4D) normal insulator, focusing on topological phase transitions at the resonant quasienergy gap. We consider two types of time-periodic driving, including a time-periodic onsite potential and a time-periodic vector potential. We reveal that both types of time-periodic driving can transform the 4D normal insulator into a 4D Floquet topological insulator characterized by an emergent second Chern number. Moreover, it is found that the topological phase of the 4D system can be modulated by tuning the strength and frequency of the time-periodic driving. Our work will be helpful for the future investigation of Floquet topological insulators in higher dimensions.

Motivated by the remarkable properties of superfluid edge dislocations in ${}^4\mathrm{He}$, we discuss a broad class of quantum systems—boundaries in phase-separated lattice states, magnetic domain walls, and ensembles of Luttinger liquids—that can be classified as transverse quantum fluids (TQFs). After introducing the general idea of a TQF, we focus on a coupled array of Luttinger liquids forming an incoherent TQF. This state is a long-range ordered quasi-one-dimensional superfluid, topologically protected against quantum phase slips by the tight binding of instanton dipoles, that has no coherent quasiparticle excitations at low energies. An incoherent TQF is a striking example of the irrelevance of the Landau quasiparticle criterion for superfluidity in systems that lack Galilean invariance. We detail its phenomenology, to motivate a number of experimental studies in condensed matter and cold atomic systems.

The synthesis, structural analysis, and physical properties of dichalcogenide families ${\mathrm{Pd}}_{1\text{−}x}{\mathrm{Ir}}_x{\mathrm{Te}}_2$ and ${\mathrm{Pd}}_{1\text{−}x}{\mathrm{Rh}}_x{\mathrm{Te}}_2$ with $0\le x\le 1$ are reported. All compositions show layered structures belonging to the $P\overline{3}m1$ space group at room temperature. These dichalcogenides show $\rho \sim T^2$ regime at low temperatures, indicating a strong electron-electron coupling. At high temperatures, the observed regime is $\rho \sim T$, associated to electron-phonon coupling. These regimes are characteristic of a Fermi liquid behavior. $\rho \left(T\right)$ in both families presents two metals with disordered alloys behavior associated with the residual resistivity ratio $\frac{{\rho }_0}{\rho \left(300\mathrm{K}\right)}\propto x\left(1-x\right)$ where $x$ is the Ir or Rh molar fraction. Pauli paramagnetism is observed in all compositions in total agreement with a Fermi liquid behavior with an important effective mass contribution. Hole-type carriers were determined by Seebeck coefficient measurements, and we determined an entropy configuration using the Mott relation for the diffusive regime and an extra term, which is independent of temperature $(\delta )$.

Evidence is presented for a reentrant quantum paraelectric (QPE) state preceded by a dipole glass (DG) phase with a nonclassical exponent in the quantum critical regime of $\mathrm{SrF}{\mathrm{e}}_{12}{\mathrm{O}}_{19}$. It is shown that the DG transition is accompanied by a spin glass (SG) transition. Further, the ergodic symmetry-breaking temperatures for the DG and SG transitions coincide ($T_{\mathrm{DG}}\sim T_{\mathrm{SG}}$) within $\pm 1$ K suggesting that $\mathrm{SrF}{\mathrm{e}}_{12}{\mathrm{O}}_{19}$ exhibits a canonical multiglass state. It is shown that these transitions are coupled through biquadratic and lower order couplings of two diverse order parameter fields. The stability of the dipole glass state is enhanced magnetically as evidenced by the increase in the freezing temperature with magnetic field ($H$). The reentrant QPE state, on the other hand, is found to give way to another frequency-dependent peak in the temperature dependence of dielectric constant, most likely a DG phase, under dc magnetic field ($H$). Further, this transition is not linked to any magnetic transition, in sharp contrast to the higher temperature multiglass transition. The transition temperature of this phase decreases with increasing magnetic field for a fixed frequency unlike the higher temperature DG transition. This raises the possibility of locating a quantum critical point (QCP) in this system at a higher magnetic field than that used in the present work. These results are discussed in the light of quantum critical models of multiferroic transitions. Our results highlight the need for more theoretical studies specific to multiferroic quantum criticality in multiglass systems.

Heterointerfaces between ferromagnetic and antiferromagnetic materials play an important role in the development and applications of magnetic and electronic devices. Here, atomic and electronic structures of two types of ${\mathrm{Fe}}_3{\mathrm{O}}_4\text{/}\mathrm{FeO}$ interfaces with different magnetic coupling modes have been investigated by combining advanced transmission electron microscopy and first-principles calculations. It is found that the ${\mathrm{Fe}}_3{\mathrm{O}}_4\text{/}\mathrm{FeO}$ (001) and ${\mathrm{Fe}}_3{\mathrm{O}}_4\text{/}\mathrm{FeO}$ (111) interfaces can be formed between FeO and ${\mathrm{Fe}}_3{\mathrm{O}}_4$ due to different phase transformations. The ${\mathrm{Fe}}_3{\mathrm{O}}_4\text{/}\mathrm{FeO}$ (111) interface is generally closer to the steady state. The electronic structure of both types of ${\mathrm{Fe}}_3{\mathrm{O}}_4\text{/}\mathrm{FeO}$ interfaces changes significantly, which leads to a metal-insulator transition of the ${\mathrm{Fe}}_3{\mathrm{O}}_4$ layer at the interfaces. The energy difference between the ferromagnetic and antiferromagnetic coupling states across the ${\mathrm{Fe}}_3{\mathrm{O}}_4\text{/}\mathrm{FeO}$ interfaces is very small, indicating that magnetic flip-flopping easily occurs in the ${\mathrm{Fe}}_3{\mathrm{O}}_4\text{/}\mathrm{FeO}$ system. The atomic magnetic moment of the interfacial Fe atoms at the ${\mathrm{Fe}}_3{\mathrm{O}}_4\text{/}\mathrm{FeO}$ (001) interface decreases by ∼10% due to the preferentially occupied $d_{\mathrm{xz}}$ and $d_{\mathrm{yz}}$ orbitals, while that at the ${\mathrm{Fe}}_3{\mathrm{O}}_4\text{/}\mathrm{FeO}$ (111) interface remains almost unchanged. These findings suggest that the ${\mathrm{Fe}}_3{\mathrm{O}}_4$/FeO interfaces are susceptible to magnetic coupling transition and may find applications in low-power consumption magnetic and electronic devices.

${\mathrm{CePd}}_3{\mathrm{S}}_4$ exhibits interplay between ferromagnetism (FM), quadrupolar order, and the Kondo effect at low temperatures with a FM transition temperature that is much higher than the value expected from the de Gennes scaling of the heavier $R{\mathrm{Pd}}_3{\mathrm{S}}_4$ compounds. In this work, we investigated the electrical transport and magnetic properties of ${\mathrm{CePd}}_3{\mathrm{S}}_4$ under pressure up through 12 GPa to better understand the interplay between electronic and magnetic phases in this material. Our findings show that the low-pressure FM state is suddenly replaced by a magnetically ordered phase that is most likely antiferromagnetic that spans from $\sim 7$ to $\sim 11$ GPa. Whereas this could be described as an example of avoided quantum criticality, given that clear changes in resistance and Hall data are detected near 6.3 GPa for all temperatures below 300 K, it is also possible that the change in ground state is a response to a pressure-induced change in structure. The lack of any discernible change in the pressure dependence of the room-temperature unit-cell parameter-volume across this whole pressure range suggests that this change in structure is either more subtle than could be detected by our measurements (i.e., development of weak wave vector) or the transition is electronic (such as a Lifshitz transition).

As the ultimate one-dimensional (1D) systems, ordered assemblies of monatomic chains, bound stably on the surface of thin atomic layers with good transferability, attachability, and twistability, can be used to construct innovative quantum structures from the ground up. Although atomic chains have been realized on high-index vicinal crystalline planes, metal surfaces, etc., their easy exfoliation, displacement, and shape manipulation remain difficult due to the rigidity of the solid templates. Phosphorene has intriguing physical and electronic properties, most notably in its tunable strain engineering capability and anisotropic structures. Previous studies, especially the structural response under stresses, have predominately been limited to 0 K, with phosphorene's accurate behaviors at room temperature yet to be comprehensively explored. Here, we report a computational study based on density functional theory at 300 K, which uncovers a twinning-mediated structural transformation in phosphorene in response to in-plane strains, in contrast to the conventional understanding of its intrinsic properties. Interestingly, the discovered 1D twinning channel with strong capabilities to capture and localize free atoms demonstrates its potential as an outstanding template in the construction of diverse self-assembled, long-range-ordered monatomic chains. Most importantly, aided by the inherent flexibility of phosphorene film, the monatomic chains can be easily transferred and attached to couple with other systems, or manipulated into a variety of curvilinear formations that possess unique spin configurations. This work is potentially extendable to other phosphorene analogs, enriching the toolbox for the development of transferable, attachable, and twistable atomic nanoarchitectures and paving the way to new paths for the fundamental study of low-dimensional systems.

We show that the characteristic function of the probability distribution associated with the change of an observable in a two-point measurement protocol with a perturbation can be written as an autocorrelation function between an initial state and a certain unitary evolved state by an effective unitary operator. Using this identification, we probe how the evolved state spreads in the corresponding conjugate space, by defining a notion of the complexity of the spread of this evolved state. For a sudden quench scenario, where the parameters of an initial Hamiltonian (taken as the observable measured in the two-point measurement protocol) are suddenly changed to a new set of values, we first obtain the corresponding Krylov basis vectors and the associated Lanczos coefficients for an initial pure state, and define the associated spread complexity. Interestingly, we find that in such a protocol, the Lanczos coefficients can be related to various cost functions used in the geometric formulation of circuit complexity, for example, the one used to define Fubini-Study complexity. We illustrate the evolution of spread complexity both analytically, by using Lie algebraic techniques, and also by performing numerical computations. This is done for cases when the Hamiltonian before and after the quench are taken as different combinations of chaotic and integrable spin chains. We show that the spread complexity saturates for large values of the parameter only when the prequench Hamiltonian is chaotic. Furthermore, in these examples, we also discuss the importance of the role played by the initial state, which is determined by the time-evolved perturbation operator.