A comparative study of the gaps measured in two techniques, angle-resolved photoelectron spectroscopy and spectroscopic imaging scanning tunneling microscopy, is presented. In particular the study focuses on the more overdoped region of the cuprate phase diagram in the superconducting state. While the total densities of states measured in the two techniques agree very well, it is shown that the peak in the density of states, ${\mathrm{\Delta }}_{\mathrm{DOS}}$, is consistently displaced to higher energies relative to the maximal superconducting gap, ${\mathrm{\Delta }}_0$, determined in photoemission. The difference between the two gaps is more evident for the less doped samples reflecting increased normalization of bands. This observation will clearly influence the boundaries in the phase diagrams of the cuprates defined by these two techniques.

We derive a Kubo-like formula for the thermal Hall conductance of a 2d lattice systems which is free from ambiguities associated with the definition of energy magnetization. We use it to define a relative topological invariant of gapped 2d lattice systems at zero temperature. Up to a numerical factor, it can be identified with the difference of chiral central charges for the corresponding edge modes. This establishes the bulk-boundary correspondence for the chiral central charge. We also show that for any local commuting projector Hamiltonian, the relative chiral central charge vanishes, while for free fermionic systems, it is related to the zero-temperature electric Hall conductance via the Wiedemann-Franz law.

In this work, we present an atomistic first-principles framework for modeling the low-temperature electronic and transport properties of disordered two-dimensional (2D) materials with randomly distributed point defects (impurities). The method is based on the $T$-matrix formalism in combination with realistic density-functional theory descriptions of the defects and their scattering matrix elements. From the $T$-matrix approximations to the disorder-averaged Green's function and the collision integral in the Boltzmann transport equation, the method allows calculations of, e.g., the density of states including contributions from bound defect states, the quasiparticle spectrum and the spectral linewidth (scattering rate), and the conductivity/mobility of disordered 2D materials. We demonstrate the method by examining these quantities in monolayers of the archetypal 2D materials graphene and transition metal dichalcogenides contaminated with vacancy defects and substitutional impurity atoms. By comparing the Born and $T$-matrix approximations, we also demonstrate a strong breakdown of the Born approximation for defects in 2D materials manifested in a pronounced renormalization of, e.g., the scattering rate by the higher-order $T$-matrix method. As the $T$-matrix approximation is essentially exact for dilute disorder, i.e., low defect concentrations ($c_{\text{dis}}\ll 1$) or density ($n_{\text{dis}}\ll A_{\text{cell}}^{-1}$ where $A_{\text{cell}}$ is the unit-cell area), our first-principles method provides an excellent framework for modeling the properties of disordered 2D materials with defect concentrations relevant for devices.

Magnetization measurements and time-of-flight neutron powder-diffraction studies on the high-temperature (300–980 K) magnetism and crystal structure (321–1200 K) of a pulverized ${\mathrm{YCrO}}_3$ single crystal have been performed. Temperature-dependent inverse magnetic susceptibility coincides with a piecewise linear function with five regimes, with which we fit a Curie-Weiss law and calculate the frustration factor $f$. The fit results indicate a formation of magnetic polarons between 300 and 540 K and a very strong magnetic frustration. By including one factor $\eta$ that represents the degree of spin interactions into the Brillouin function, we can fit well the applied-magnetic-field dependence of magnetization. No structural phase transition was observed from 321 to 1200 K. The average thermal expansions of lattice configurations ($a$, $b$, $c$, and V) obey well the $\mathrm{Gr}\ddot{\mathtt{u}}\mathrm{neisen}$ approximations with an anomaly appearing around 900 K, implying an isosymmetric structural phase transition, and display an anisotropic character along the crystallographic $a$, $b$, and $c$ axes with the incompressibility $K_0^a>K_0^c>K_0^b$. It is interesting to find that at 321 K, the local distortion size $\mathrm{\Delta }$(O2) $\approx 1.96\mathrm{\Delta }$(O1) $\approx 4.32\mathrm{\Delta }$(Y) $\approx 293.89\mathrm{\Delta }$(Cr). Based on the refined Y-O and Cr-O bond lengths, we deduce the local distortion environments and modes of Y, Cr, O1, and O2 ions. Especially, the Y and O2 ions display obvious atomic displacement and charge subduction, which may shed light on the dielectric property of the ${\mathrm{YCrO}}_3$ compound. Additionally, by comparing Kramers ${\mathrm{Mn}}^{3+}$ with non-Kramers ${\mathrm{Cr}}^{3+}$ ions, it is noted that being a Kramers or non-Kramers ion can strongly affect the local distortion size, whereas, it may not be able to change the detailed distortion mode.

Topological Weyl semimetals (WSMs) have attracted widespread interest due to the chiral Weyl fermions and surface Fermi arcs that enable unique optical and transport phenomena. In this work, we present angle-resolved Raman spectroscopy of TaP, a prototypical noncentrosymmetric WSM, for five excitation wavelengths ranging from 364 to 785 nm. The Raman-active modes, $A_1$, $B_1^1$, and $B_1^2$ modes, exhibit two main unique features beyond the conventional Raman theory. First, the relative intensities of Raman-active modes change as a function of the excitation wavelength. Second, angle-resolved polarized Raman spectra show systematic deviation from the Raman tensor theory. In particular, the $B_1^1$ mode is absent for 633-nm excitation, whereas the $B_1^2$ mode shows an unusual twofold symmetry instead of a fourfold symmetry for 488-, 532-, and 633-nm excitations. These unconventional phenomena are attributed to the interference effect in the Raman process owing to the existence of multiple carrier pockets with almost the same energy but different symmetries.

We investigated the field-sweep-rate and time dependence of the transverse resistivity anomalies in ultrathin $\mathrm{SrRu}{\mathrm{O}}_3$ epitaxial thin films the behaviors of which resemble what has been claimed to be the topological Hall effect. We find that the magnitudes of the anomalies are independent of the field sweep rate, while the magnetic field at which the anomalies appear $\left(H_{\mathrm{hump}}\right)$ and the coercive field $\left(H_c\right)$ exhibit identical sweep-rate dependence. We also show that the transverse resistivity under a fixed external magnetic field exhibits transient behavior, eventually (≈5000 s) approximating the value of the anomalous Hall resistivity that is obtained after the magnetization reversal processes are completed. These results indicate that $H_c$ is inhomogeneous within the films and activation energies of the magnetization reversal at $H_{\mathrm{hump}}$ and $H_c$ are identical. The observed field-sweep-rate and time dependence of the transverse resistivity anomalies can be understood in the framework of conventional magnetic switching dynamics, and topological interpretation would not be necessarily taken into account. Our results are in line with a model in which inhomogeneity of $H_c$ and anomalous Hall resistivity are responsible for the transverse resistivity anomalies in $\mathrm{SrRu}{\mathrm{O}}_3$.

We report pressure evolution of charge density wave (CDW) order and the emergence of superconductivity (SC) in $1\mathit{T}\text{−}{\mathrm{VSe}}_2$ single crystal by studying resistance and magnetoresistance behavior under high pressure. With increasing quasihydrostatic pressure the CDW order enhances with its ordering temperature ($\sim 100\mathrm{K}$ at ambient P) increasing marginally up to 5 GPa. At higher pressures, CDW-like resistance anomaly increases more rapidly with the characteristic temperature reaching $\sim 290\mathrm{K}$ at 14.2 GPa. Upon further increase of pressure, the resistance anomaly due to CDW order gets suppressed drastically with rapidly increased metallicity (as clearly evidenced from the increased RRR value) and superconductivity emerges at $\sim 15$ GPa, with the onset critical temperature ($T_c$) $\sim 4$ K. The pressure dependence of $T_c$ is found negligible, different from an increase or a dome-shaped behavior seen in isostructural layered diselenide superconductors. The high-pressure magnetoresistance and Hall measurements suggest successive electronic structural changes with Fermi surface modifications at 5 and $\sim 12$ GPa.

By using the momentum-space Lanczos recursive method which considers rigorously all multiple-scattering events, we unveil that the nonperturbative disorder effect has a dramatic impact on the charge transport of a two-dimensional electron system with Rashba spin-orbit coupling in the low-density region. Our simulations find a power-law dependence of the dc longitudinal conductivity on the carrier density, with the exponent linearly dependent on the Rashba spin-orbit strength but independent of the disorder strength. Therefore, the classical charge transport influenced by complicated multiple-scattering processes also shows the characteristic feature of the spin-orbit coupling. This highly unconventional behavior is argued to be observable in systems with tunable carrier density and Rashba splitting, such as the ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ interface, the heterostructure of Rashba semiconductors bismuth tellurohalides, and the surface alloy ${\mathrm{Bi}}_x{\mathrm{Pb}}_y{\mathrm{Sb}}_{1-x-y}/\mathrm{Ag}\left(111\right)$.

We consider the quantum Ising chain with uniformly distributed random antiferromagnetic couplings $(1\le J_i\le 2)$ and uniformly distributed random transverse fields $\left({\mathrm{\Gamma }}_0\le {\mathrm{\Gamma }}_i\le 2{\mathrm{\Gamma }}_0\right)$ in the presence of a homogeneous longitudinal field, $h$. Using different numerical techniques (density-matrix renormalization group, combinatorial optimization, and strong disorder renormalization group methods) we explore the phase diagram, which consists of an ordered and a disordered phase. At one end of the transition line $\left(h=0,{\mathrm{\Gamma }}_0=1\right)$ there is an infinite disorder quantum fixed point, while at the other end $\left(h=2,{\mathrm{\Gamma }}_0=0\right)$ there is a classical random first-order transition point. Close to this fixed point, for $h>2$ and ${\mathrm{\Gamma }}_0>0$ there is a reentrant ordered phase, which is the result of quantum fluctuations by means of an order through disorder phenomenon.

We consider a one-dimensional spin chain system with quenched disorder and in the presence of a local periodic drive. We study the time evolution of the system in the Floquet basis and evaluate the fidelity susceptibility, which is a measure of how a given state changes under a small perturbation, of states to a weak periodic drive. We demonstrate that the statistical properties of the fidelity susceptibility over different disorder realizations can be used to identify two phases of the system: (1) the many-body localized phase, in which the susceptibility exhibits long tails while its average value decreases rapidly as disorder increases, and (2) the ergodic phase, in which the susceptibility distribution is narrow and its average value weakly depends on disorder. This distinction in the average value of the susceptibility between the two phases develops readily for systems with ten or more spins. Therefore, recently built networks of qubits subject to a local drive can simulate dynamics of a system in the many-body localization regime. We also show that the spin accumulation speed is correlated with the fidelity susceptibility and can also be used to distinguish the two phases.

We compute the $K$- and $L_3$-edge resonant inelastic x-ray-scattering (RIXS) spectrum of the columnar and the staggered quantum dimer states accessible to the square lattice Heisenberg magnet. Utilizing a bond-operator representation mean-field theory we investigate the RIXS features of the one- and two-triplon excitation spectrum supported by the quantum dimer model in the background of condensed singlet excitation. We find that the two-triplon excitation boundary lies within an energy range of $2.7J_2\left(1.7J_2\right)$ to $9J_2\left(7.5J_2\right)$ for the columnar (staggered) phase, where $J_2$ is the interbond coupling strength. We estimated the two-triplon gap to be $2.7J_2$ $\left(1.7J_2\right)$ for the columnar (staggered) dimer phase. The highest intensity of the $K$-edge RIXS spectrum is localized approximately around the $(\pi /2,\pi /2)$ point for both the columnar and the staggered phases. At the $L_3$ edge we study the one- and two-triplon signal considering experimental scattering geometry, polarization restriction, and experimental resolution effects. Our calculations find a contribution to the two-triplon RIXS signal that originates from the local hard-core dimer constraint. This leads to a finite nonzero signal at the (0,0) momentum transfer which can offer an explanation for the existing ladder RIXS experiments and also predicts a nonzero signal for the two-dimensional quantum dimer system. We find that the $L_3$-edge RIXS response of the one- and two-triplon signal could exist in antiphase rung modulation for zero and $\pi$ as found in inelastic neutron scattering. Since the disordered phase has the potential to harbor a variety of quantum paramagnetic states, our RIXS calculations provide useful signatures to identify the true nature of the ordering pattern.

Monolayer transition metal dichalcogenides (TMDs) offer a novel two-dimensional platform for semiconductor devices. One such application, whereby the added low-dimensional crystal physics (i.e., optical spin selection rules) may prove TMDs a competitive candidate, are quantum dots as qubits. The band structure of TMD monolayers offers a number of different degrees of freedom and combinations thereof as potential qubit bases, primarily electron spin, valley isospin, and the combination of the two due to the strong spin-orbit coupling known as a Kramers qubit. Pure spin qubits in monolayer $\mathrm{Mo}{X}_2$ (where $X=\text{S}$ or Se) can be achieved by energetically isolating a single valley and tuning to a spin degenerate regime within that valley by a combination of a sufficiently small quantum dot radius and a large perpendicular magnetic field. Within such a TMD spin qubit, we theoretically analyze single-qubit rotations induced by electric dipole spin resonance. We employ a rotating-wave approximation within a second-order time-dependent Schrieffer-Wolf effective Hamiltonian to derive analytic expressions for the Rabi frequency of single-qubit oscillations, and optimize the mechanism or the parameters to show oscillations up to $250\mathrm{MHz}$. This is significantly faster than similar predictions found for TMD qubits in the Kramers pair spin-valley or valley-only basis as well as experimental results for conventional semiconductor devices.

In this paper we present a modified localization landscape theory to calculate localized/confined electron and hole states and the corresponding energy eigenvalues without solving a (large) eigenvalue problem. We motivate and demonstrate the benefit of solving ${\widehat{H}}^{2}u=1$ in the modified localization landscape theory in comparison to $\widehat{H}u=1$, solved in the localization landscape theory. We detail the advantages by fully analytic considerations before targeting the numerical calculation of electron and hole states and energies in III-N heterostructures. We further discuss how the solution of ${\widehat{H}}^{2}u=1$ is used to extract an effective potential $W$ that is comparable to the effective potential obtained from $\widehat{H}u=1$, ensuring that it can for instance be used to introduce quantum corrections to drift-diffusion transport calculations. Overall, we show that the proposed modified localization landscape theory keeps all the benefits of the localization landscape theory but further improves factors such as convergence of the calculated energies and the robustness of the method against the chosen integration region for $u$ to obtain the corresponding energies. We find that this becomes especially important for here studied $c$-plane InGaN/GaN quantum wells with higher In contents. All these features make the proposed approach very attractive for calculation of localized states in highly disordered systems, where partitioning the systems into different subregions may be difficult.

We extend the scope of Kitaev spin liquids to non-Archimedean lattices. For the pentaheptite lattice, which results from the proliferation of Stone-Wales defects on the honeycomb lattice, we find an exactly solvable non-Abelian chiral spin liquid with spontaneous time-reversal symmetry breaking due to lattice loops of odd length. Our findings call for potential extensions of exact results for Kitaev models which are based on reflection positivity, which is not fulfilled by the pentaheptite lattice. We further elaborate on potential realizations of our chiral spin-liquid proposal in strained $\alpha \text{−}{\mathrm{RuCl}}_3$.

The emergence of superdiffusive spin dynamics in integrable classical and quantum magnets is well established by now, but there is no generally valid theoretical explanation for this phenomenon. A fundamental difficulty is that the hydrodynamic fluctuations of conserved quasiparticle modes are purely diffusive. We argue that in isotropic integrable magnets, a complete hydrodynamic description must include soft “gauge” degrees of freedom, that arise from spontaneous breaking of the Bethe pseudovacuum symmetry. We show that the coarse-grained time evolution of these modes lies in the Kardar-Parisi-Zhang universality class of dynamics.

Confined geometries such as semiconductor quantum dots are promising candidates for fabricating quantum computing devices. When several quantum dots are in proximity, spatial correlation between electrons in the system becomes significant. In this paper, we employ a variational formulation for calculating accurate two-electron wavefunctions in configuration space, irrespective of potential geometry. To evaluate the Coulomb integrals with high accuracy, a numerical integration method using multiple Gauss quadratures is used. With this approach, we investigate the confinement of two electrons in double quantum dots, and evaluate the spatial entanglement. We investigate the dependence of spatial entanglement on various geometrical parameters. We derive the two-particle wavefunctions in the asymptotic limit of the separation distance between quantum dots and obtain universal saturation values for the spatial entanglement. Resonances in the entanglement values due to avoided level crossings of states are observed. We also demonstrate the formation of electron clusters and show that the entanglement value is a good indicator for the formation of such clusters. Further, we show that a precise tuning of the entanglement values is feasible with applied external electric fields.

Chiroptical responses of helical superstructures are determined by collective behaviors of the individual building blocks. In this paper, we present a full theoretical description of the collective resonance in superstructures. We use the gold nanorods as individual building blocks and arrange them helically along an axis in an end-to-end fashion. Numerical simulations on single unit cells reveal that the plasmonic coupling between the nanorods produces hybridized resonances, whose intensity is strongly dependent on the excitation light with left- or right-handed circular polarizations (LCP or RCP). A node-mode criterion is proposed on the basis of the microscopic mechanism, which successfully explains the difference between LCP and RCP. We further demonstrate, by repeating the unit cell from 1 to infinity along the helical axis, the multiple hybridized resonances gradually evolve and merge into a single collective resonance, whose energy is also dependent on LCP and RCP. An analytical description is provided for the collective resonance of the helical superstructure on the basis of the coupled dipole approximation method. Our theory shows that $n$ collective resonance modes are present in the helical superstructure with the unit cell consisting of $n$ nanorods. Strikingly, only one resonance can be excited by the incident light with certain circular polarization. We propose a universal selection rule for such selective excitation of the collective resonances by analyzing the symmetry of the helical superstructures. The insights provided in this work may shed light on future designs and fabrications of helical superstructures using plasmonic building blocks.