We investigate an antiferromagnetic spin-1 Heisenberg chain in the presence of Dyzaloshinskii-Moriya interactions (DMI) and an external magnetic field. We study the resulting spin chain using a combination of numerical and analytical techniques. Using DMRG simulations to determine the spectral gap and the entanglement spectrum, we map out the phase diagram as a function of magnetic field strength and DMI strength. We provide a qualitative interpretation for these numerical findings by mapping the spin-1 chain on a spin-$1/2$ ladder and using a bosonization approach.

Optical conductivity $\left[\sigma \right(\omega \left)\right]$ of ${\mathrm{CeRhIn}}_5$ and ${\mathrm{YbNi}}_3{\mathrm{Ga}}_9$ have been measured at external pressures to 10 GPa and at low temperatures to 6 K. Regarding ${\mathrm{CeRhIn}}_5$, at ambient pressure the main feature in $\sigma \left(\omega \right)$ is a Drude peak due to free carriers. With increasing pressure, however, a characteristic midinfrared (mIR) peak rapidly develops in $\sigma \left(\omega \right)$, and its peak energy and width increase with pressure. These features are consistent with an increased conduction ($c$)-$f$ electron hybridization at high pressure and show that pressure has tuned the electronic state of ${\mathrm{CeRhIn}}_5$ from very weakly to strongly hybridized ones. As for ${\mathrm{YbNi}}_3{\mathrm{Ga}}_9$, in contrast, a marked mIR peak is observed already at ambient pressure, indicating a strong $c\text{−}f$ hybridization. At high pressures, however, the mIR peak shifts to lower energy and becomes diminished and seems to merge with the Drude component at 10 GPa. Namely, ${\mathrm{CeRhIn}}_5$ and ${\mathrm{YbNi}}_3{\mathrm{Ga}}_9$ exhibit some opposite tendencies in the pressure evolution of $\sigma \left(\omega \right)$ and electronic structure. These results are discussed in terms of the pressure evolution of $c\text{−}f$ hybridized electronic states in Ce and Yb compounds, in particular in terms of the electron-hole symmetry often considered between Ce and Yb.

On the basis of a Chern-Simons field-theoretical description we propose a simple method for the derivation of model interactions for Pfaffian paired states. We verify the method in the case of the Pfaffian (i.e., Moore-Read) state and derive a general form of the model interaction in the case of the particle-hole (PH) Pfaffian. More than one Landau level is needed to establish the correlations of the PH Pfaffian, and we present the values of relevant three-body pseudopotentials for two Landau levels.

Realization of half-metallicity with a sizable minority-spin gap and ferromagnetic ordering has been a central research emphasis in the development of next-generation spintronic devices. To date, only three-dimensional half-metals have been achieved experimentally, while their counterparts based on two-dimensional (2D) materials remain to be materialized despite extensive efforts based on various predictive designs. This standing challenge is largely due to stringent requirements to establish ferromagnetic order in low-dimensional systems. Here we use first-principles approaches to show that atomically thin zigzag tungsten dichalcogenide $\mathrm{W}{X}_2$ ($X=\mathrm{S}$, Se) nanoribbons preserving the stoichiometry of $\mathrm{W}:X=1:2$ stand as highly appealing intrinsic half-metallic systems, without invoking the prevailing approaches of applying an external electric field, chemical modification, or carrier doping. The readily accessible half-metallicity is attributed to distinctly different edge reconstructions, insulating along the X-terminated edges and metallic along the self-passivated W-terminated edges; the latter are further characterized by a robust spin-polarized electron transmission channel. These findings are expected to provide indispensable elemental building blocks for spintronic applications purely based on 2D materials.

The Kekule pattern of the (anti)ferromagnetic exchange field on monolayer ${\text{MoS}}_2$ can be induced by proximity to the (111) surface of ${\text{BiFeO}}_3$ on both sides. The three-band tight binding model of the ${\text{MoS}}_2$ layer with Kekule patterned exchange field is applied to describe the heterostructures. The tight binding model is justified by the first principle calculations. The magnetization orientations of the substrates control the pattern of the exchange field, which then switches the band structures of the lowest zigzag edge states between being metallic and insulating. The lowest four zigzag edge bands provide conducting channels with a spin-polarized current. Optical excitation of carriers in these bands generates sizable spin and charge currents, which are theoretically modeled by the perturbation solution of the semiconductor Bloch equation. The injected spin currents have multiple resonant peaks at a few frequencies, which can be switched off by rotating the magnetization orientations of the substrates.

An entanglement spectrum encodes statistics beyond the entanglement entropy, of which several have been studied in the context of many-body localization. We numerically study the extreme value statistics of entanglement spectra of many-body localized eigenstates. The physical information encoded in these spectra is almost fully carried by the few smallest elements, suggesting the extreme value statistics to have physical significance. We report the surprising observation of Gumbel statistics. Our result provides an analytical, parameter-free characterization of many-body localized eigenstates.

Dirac-like Hamiltonians, linear in momentum $k$, describe the low-energy physics of a large set of novel materials, including graphene, topological insulators, and Weyl fermions. We show here that the inclusion of a minimal $k^2$ Wilson's mass correction improves the models and allows for systematic derivations of appropriate boundary conditions for the envelope functions on finite systems. Considering only Wilson's masses allowed by symmetry, we show that the $k^2$ corrections are equivalent to Berry-Mondragon's discontinuous boundary conditions. This allows for simple numerical implementations of regularized Dirac models on a lattice, while properly accounting for the desired boundary condition. We apply our results on graphene nanoribbons (zigzag and armchair), and on a PbSe monolayer (topological crystalline insulator). For graphene, we find generalized Brey-Fertig boundary conditions, which correctly describe the small gap seen on ab initio data for the metallic armchair nanoribbon. On PbSe, we show how our approach can be used to find spin-orbital-coupled boundary conditions. Overall, our discussions are set on a generic model that can be easily generalized for any Dirac-like Hamiltonian.

A physical system exposes to us in a real space, while its description often refers to its reciprocal momentum space. A connection between them can be established by exploring patterns of quasiparticles interference (QPI), which is experimentally accessible by Fourier transformation of the scanning tunneling spectroscopy. We here investigate how local and global features of QPI patterns are related to the geometry and topology of electronic structure in the considered physical system. A reduced response function (RRF) approach is developed that can analyze QPI patterns with clear physical pictures. The generalized joint density of states, which is the imaginary part of RRF, is justified for studying QPI. Moreover, we reveal that global patterns of QPI may be indicators of topological numbers for gapless systems, and we demonstrate the robustness of such indicators against distractive local features of QPI for topological materials with complicated band structures.

Motivated by the recent experimental observation of the topological Anderson insulator in disordered atomic wires based on the Su-Schrieffer-Heeger (SSH) model, we study disorder effects on a dimerized Kitaev superconductor chain, which is regarded as the superconductor version of the SSH model. By computing the real-space winding number and the zero-bias differential conductance, we analyze the topological phase transitions occurring in a dimerized Kitaev superconductor chain with disorder. It is found that disorder can induce a topologically nontrivial superconductor phase hosting Majorana zero modes (MZMs). We can regulate the appearance of disorder-induced MZMs by adjusting the dimerization parameter. Finally, we use the self-consistent Born approximation method to verify the numerical results.

Water molecules at solid surfaces typically arrange in layers. The physical origin of the hydration layers is usually explained by two different reasons: (1) the attraction between the surface and water and (2) the water confinement due to the surface. While the attraction is specific to the particular solid, the confinement is a general property of surfaces; a differentiation between the two effects is, therefore, critical for research on interactions at aqueous interfaces. Here, we investigate the graphite-water interface, which is a widely used model system where the solid-water attraction is often considered to be negligible. Similar to previous studies, we observe hydration layers using three-dimensional atomic force microscopy at the graphite-water interface. We explain why the confinement could cause the formation of hydration layers even in the absence of attraction between surface and water by employing Monte Carlo simulations. Using additional molecular dynamics simulations, we continue to show that at ambient conditions, however, the confinement alone does not cause the formation of layers at the graphite-water interface. We thereby demonstrate that there is a significant graphite-water attraction.

Rotating all islands in square artificial spin ice (ASI) uniformly about their centers gives rise to the recently reported pinwheel ASI. At angles around ${45}^{\circ }$, the antiferromagnetic ordering changes to ferromagnetic and the magnetic configurations of the system exhibit near degeneracy, making it particularly sensitive to small perturbations. We investigate through micromagnetic modeling the influence of dipolar fields produced by physically extended islands in field-driven magnetization processes in pinwheel arrays and compare the results to hysteresis experiments performed in situ using Lorentz transmission electron microscopy. We find that magnetization end states induce a Heisenberg pseudoexchange interaction that governs both the interisland coupling and the resultant array reversal process. Symmetry reduction gives rise to anisotropies and array-corner mediated avalanche reversals through a cascade of nearest-neighbor (NN) islands. The symmetries of the anisotropy axes are related to those of the geometrical array but are misaligned to the array axes as a result of the correlated interactions between neighboring islands. The NN dipolar coupling is reduced by decreasing the island size and, using this property, we track the transition from the strongly coupled regime towards the pure point dipole one and observe modification of the ferromagnetic array reversal process. Our results shed light on important aspects of the interactions in pinwheel ASI and demonstrate a mechanism by which their properties may be tuned for use in a range of fundamental research and spintronic applications.

Recently, superconductivity in BaPtAs with the noncentrosymmetric SrPtSb and the centrosymmetric YPtAs-structure has been discovered. Its noncentrosymmetric and centrosymmetric structures make BaPtAs a charming compound for searching the effect of spin-orbit coupling (SOC) onto superconductors with broken and preserved spatial inversion symmetry. We have investigated the effect of SOC on the physical and electron-phonon interaction properties of these phases of BaPtAs by using the generalized gradient approximation of the density functional theory and the plane-wave pseudopotential method. The inclusion of SOC has moderate effect on the elastic and electronic properties, and on phonon frequencies for both phases of BaPtAs. However, SOC makes an opposite impact on their Eliashberg spectral function. For the noncentrosymmetric phase, this coupling decreases the strength of dominant peaks of Eliashberg spectral function, reducing the values of average electron-phonon coupling and superconducting transition temperature. The scenario is exactly opposite for the centrosymmetric phase. For both phases, the hybridized Pt-As vibrations play a strongly significant role in determining their electron-phonon interaction properties since their electronic states have the dominant contribution near the Fermi level. The superconducting temperature is estimated to be 2.87 K for the SrPtSb phase and 2.38 K for the YPtAs phase. These values compare well with the reported measured values of 2.8 K and 2.1–3.0 K, respectively.

The electron charge density distribution of materials is one of the key quantities in computational materials science as theoretically it determines the ground state energy and practically it is used in many materials analyses. However, the scaling of density functional theory calculations with number of atoms limits the usage of charge-density-based calculations and analyses. Here we introduce a machine-learning scheme with local-environment-based graphs and graph convolutional neural networks to predict charge density on grid points from the crystal structure. We show the accuracy of this scheme through a comparison of predicted charge densities as well as properties derived from the charge density, and that the scaling is $O$($N$). More importantly, the transferability is shown to be high with respect to different compositions and structures, which results from the explicit encoding of geometry.

We examine coherent phonons in a strongly driven sample of optimally-doped high temperature superconductor ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$. We observe a nonlinear lattice response of the 4.5 THz copper-oxygen vibrational mode at high excitation densities, evidenced by the observation of the phonon third harmonic and indicating the mode is strongly anharmonic. In addition, we observe how high-amplitude phonon vibrations modify the position of the electronic charge transfer resonance. Both of these results have important implications for possible phonon-driven nonequilibrium superconductivity.

The cubic chiral helimagnets with the $P{2}_{1}3$ space group represent a group of compounds in which the stable skyrmion-lattice state is experimentally observed. The key parameter that controls the energy landscape of such systems and determines the emergence of a topologically nontrivial magnetic structure is the Dzyaloshinskii-Moriya interaction (DMI). Chemical substitution is recognized as a convenient instrument to tune the DMI in real materials and has been successfully utilized in studies of a number of chiral magnets, such as MnSi, FeGe, MnGe, and others. In our study, we applied small-angle neutron scattering to investigate how chemical substitution influences the skyrmionic properties of an insulating helimagnet ${\mathrm{Cu}}_2{\mathrm{OSeO}}_3$ when Cu ions are replaced by either Zn or Ni. Our results demonstrate that the DMI is enhanced in the Ni-substituted compounds $(\mathrm{Cu},{\mathrm{Ni})}_2{\mathrm{OSeO}}_3$, but weakened in $(\mathrm{Cu},{\mathrm{Zn})}_2{\mathrm{OSeO}}_3$. The observed changes in the DMI strength are reflected in the magnitude of the spin-spiral propagation vector and the temperature stability of the skyrmion phase.

We have executed ab initio pseudopotential calculations on the structural, electronic, elastic, mechanical, vibrational, and electron-phonon interaction properties of hexagonal ZrRuP (h-ZrRuP) and orthorhombic ZrRuP (o-ZrRuP). The electronic states of both phases near the Fermi energy are found to be dominated by the $d$ electrons of transition metal atoms, suggesting that they play a more active role in the generation of superconducting state for both phases of ZrRuP. A critical assessment of their elastic and mechanical properties reveals that the lattice of h-ZrRuP is softer than that of o-ZrRuP. A comparison of phonon dispersion curves for both phases indicates that the lower transverse acoustic branch of h-ZrRuP is much softer than that of o-ZrRuP. The soft character of this phonon branch gives rise to strong electron-phonon interaction in h-ZrRuP. Therefore the electron-phonon coupling parameter for h-ZrRuP equals to 1.25 which is considerably larger than the corresponding value of 0.57 for o-ZrRuP. As a consequence, phonon and electron-phonon interaction properties are crucial in making superconducting transition temperature much higher for h-ZrRuP than o-ZrRuP. At the end, the value of this temperature is found to be 12.49 K for h-ZrRuP and 3.89 K for o-ZrRuP which coincide with their experimental values of 12.93 and 3.82 K.

Two-dimensional (2D) topological materials (TMs) have attracted tremendous attention due to the promise of revolutionary devices with nondissipative electric or spin currents. Unfortunately, the scarcity of 2D TMs holds back the experimental realization of such devices. In this work, based on our recently developed, highly efficient TM discovery algorithm using symmetry indicators, we explore the possible 2D TMs in all nonmagnetic compounds in four recently proposed materials databases for possible 2D materials. We identify hundreds of 2D TM candidates, including 205 topological (crystalline) insulators and 299 topological semimetals. In particular, we highlight MoS, with a mirror Chern number of −4, as a possible experimental platform for studying the interaction-induced modification to the topological classification of materials. Our results winnow out the topologically interesting 2D materials from these databases and provide a TM gene pool for further experimental studies.

We study the entanglement Hamiltonian (EH) associated with the reduced density matrix of free fermion models in a delocalized-localized Anderson phase transition. We show numerically that the structure of the EH matrix differentiates the delocalized from the localized phase. In the delocalized phase, EH becomes a long-range Hamiltonian but is short-range in the localized phase, no matter what the configuration of the system's Hamiltonian is (whether it is long- or short-range). With this view, we introduce the entanglement conductance (EC), which quantifies how much EH is long-range, and we propose it as an alternative quantity to measure entanglement in the Anderson phase transition, by which we locate the phase transition point of some one-dimensional free fermion models. In addition, by applying the finite-size method to the EC, we find three-dimensional Anderson phase transition critical disorder strength.