Clean quasi-one-dimensional systems demonstrate Van Hove singularities in the density of states $\nu$ and resistivity $\rho$, occurring when the Fermi level crosses the bottom of some transversal quantization subband. However, taking the scattering on impurities into the account should smear the singularities. As we have shown in our previous work [Phys. Rev. B 99, 035414 (2019)], for the case of clean conducting tubes, the character of smearing strongly depends on the impurity concentration $n$. For $n\gg n_c$, the singularities are simply rounded, while for $n\ll n_c$, the initial peak is asymmetrically split into two for the case of attracting impurities, $n_c$ being a crossover concentration. In this work, we extend our consideration to “strips”—quasi-one-dimensional structures in 2D conductors. Here also for $n\ll n_c$, an original Van Hove singularity is asymmetrically split into two peaks. However, in contrast to the tube case, the amplitudes of scattering at impurities depend on their positions and these peaks are inhomogeneously broadened. The strongest broadening occurs in the left peak, arising, for attracting impurities, due to the scattering at the quasistationary levels that form a relatively broad impurity band with a weak quasi-Van Hove feature on its lower edge. Different parts of $\rho \left(\varepsilon \right)$ are dominated by different groups of impurities: close to the minimum the most effective scatterers, paradoxically, are the “weakest” impurities located close to nodes of the electronic wave function. The quasi-Van Hove feature at the left maximum is dominated by the strongest impurities located close to antinodes.

Cubic spinel ${\mathrm{GeNi}}_2{\mathrm{O}}_4$ exhibits intriguing magnetic properties with two successive antiferromagnetic phase transitions $(T_{N1}\approx 12.1$ and $T_{N2}\approx 11.4\mathrm{K})$ with the absence of any structural transition. We have performed detailed heat-capacity and magnetic measurements in different crystallographic orientations. A magnetic phase in the presence of the magnetic field $(H\ge 4\mathrm{T})$ along the [111] direction is revealed, which is not observed when the magnetic field is applied along the [100] and [110] directions. High-field neutron powder-diffraction measurements confirm such a change in the magnetic phase, which could be ascribed to a spin reorientation in the presence of the magnetic field. A strong magnetic anisotropy and competing magnetic interactions play a crucial role in the complex magnetic behavior in this cubic system.

We study the dependence of the Dzyaloshinskii-Moria interaction (DMI) using the $s\text{−}d$ model in the bilayer ferromagnet/heavy-metal system on the mechanical strain applied to the system. We show that DMI is sensitive to the strain perpendicular to the film plane. It can vary 40% under the strain of 0.3%. Such a strong variation is in agreement with recent experiment [Phys. Rev. Lett. 124, 157202 (2020)]. The DMI coefficient variation is mostly related to the change of the distance between heavy-metal atomic planes under the strain. Changing the in-plane distance between the heavy-metal ions does not produce strong variation of DMI. Anisotropy of the DMI interaction may appear if the strain is anisotropic in the plane of the bilayer. The DMI anisotropy is related to the anisotropy of the electron effective mass in the film plane induced by the strain.

Superconductor–topological insulator (SC-TI) heterostructures were proposed to be a possible platform to realize and control Majorana zero modes. Despite experimental signatures indicating their existence, univocal interpretation of the observed features demands theories including realistic electronic structures. To achieve this, we solve the Kohn–Sham–Dirac–Bogoliubov–de Gennes equations for ultrathin ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ films on superconductor palladium telluride within the fully relativistic Korringa-Kohn-Rostoker method and investigate quasiparticle spectra as a function of chemical potential and film thickness. We find multiple proximity-induced gaps where the gap sizes highly depend on characteristics of the TI states. The TI Dirac interface state is relevant to the induced gap only when the chemical potential is close to the Dirac-point energy. Otherwise, at a given chemical potential, the largest induced gap arises from the highest-energy quantum-well states, whereas the smallest gap arises from the TI topological surface state with its gap size depending on the TI pairing potential.

We report two reversible pressure-induced isosymmetric phase transitions in $\alpha -\mathrm{A}{\mathrm{g}}_2\mathrm{S}$ that are accompanied by two compressive anomalies at 7.5 and 16 GPa, respectively. The first transition arises from a sudden and drastic puckering of the wrinkled Ag-S layers, which leads to an anomalous structural softening at high pressure and gives rise to the ultrahigh compressive ductility in $\alpha -\mathrm{A}{\mathrm{g}}_2\mathrm{S}$. The second transition stems from a pressure-driven electronic state crossover from a conventional semiconductor to a topological metal. The band-crossing points near the Fermi energy form a nodal-line structure due to the preservation of the time-reversal and space-inversion symmetries under pressure. Our findings not only reveal the underlying mechanism responsible for the ultrahigh ductility in this class of inorganic semiconductors, but also provide a distinctive member to the growing family of topological metals and semimetals.

Interatomic potential plays a key role in ensuring the accuracy and reliability of molecular-dynamics simulation results. While most empirical potentials are benchmarked against a set of carefully chosen bulk material properties, recent advances in machine learning have seen the emergence of neural-network-based mathematical potentials capable of describing highly complex potential energy surfaces for a variety of systems. We report here the development of a neural-network interatomic potential (NNIP) with modified embedded-atom method background density as fingerprint functions, which could accurately model the energetics of metallic nanoparticles and clusters (Cu as a representative example) widely used in catalysis. To appropriately account for the diverse chemical environments encountered in nanoparticles/nanoclusters, an extensive set of atomic configurations (totaling 18 084) were calculated using density-functional-theory (DFT) at the Perdew-Burke-Ernzerhof level. In addition to standard bulk properties such as cohesive energies and elastic constants, the sampled configurations also include a substantial number of differently oriented crystal facets and differently sized nanoparticles and nanoclusters, greatly expanding the value range of NNIP features that was otherwise quite limited. The complex energy potential surface of Cu can be faithfully reproduced, with an average error of 0.011 eV/at for energy states within 3 eV of the ground state. As an illustration, the developed NNIP is used to simulate the molecular dynamics of copper nanoparticles, and good agreement is achieved between DFT and the NNIP.

For polycrystalline exchange-biased thin films the macroscopic magnetic properties evolve from a complex interplay of different individual magnetic anisotropies which are directly connected to the grain volume distribution and to the crystal and interface structure of the layer system. A quantitative comparison of models describing a macroscopically observed exchange bias by the contributing anisotropies has in most cases been hampered by neglecting their time dependence with respect to data acquisition and storage times. Using a recently developed model we are able to connect time-dependent parts of the prevailing anisotropies with parameters describing the polycrystalline structure of the layer system. The model will be compared to experiments on a prototypical IrMn/CoFe bilayer, where structural and magnetic parameters have been systematically altered by varying the deposition rate of the antiferromagnetic layer and the field-cooling temperature. The combination of angular-resolved measurements obtained by vectorial magneto-optic Kerr magnetometry and a systematic analysis of the polycrystalline structure enables the disentanglement of the different anisotropy contributions to the macroscopic exchange bias and coercive fields and serves as a verification of the utilized model.

In spintronics, simultaneous realization of high tunneling magnetoresistance and low resistivity in magnetic tunnel junctions (MTJs) is challenging because insulating layers with higher barrier heights generally generate highly spin-polarized currents but increase resistivity. We overcome this trade-off relationship using Brillouin-zone-folded bands at the interfaces in the Fe/spinel ${\mathrm{MgGa}}_2{\mathrm{O}}_4/\mathrm{Fe}\mathrm{MTJ}$. Interfacial resonant states that enhance conductance are formed by folded bands, with Fe–O hybridization playing a key role in the resonant effect intensity at the Fermi level. The electronegativity of cation Ga in spinel oxide ${\mathrm{MgGa}}_2{\mathrm{O}}_4$ is found to be a crucial physical quantity to control an intensity of the interfacial-resonant effect from the comparative analysis with the ${\mathrm{MgAl}}_2{\mathrm{O}}_4$-based MTJ.

In this work we numerically studied disordered quantum transport in a quantum anomalous Hall insulator-superconductor junction based on the effective edge model approach. In particular, we focus on the parameter regime with the mean-free path due to elastic scattering much smaller than the sample size and superconductor coherence length, and discuss disordered transport behavior in the presence of different numbers of chiral edge modes, as well as nonchiral metallic modes. Our numerical results demonstrate that the presence of multiple chiral edge modes or nonchiral metallic modes will lead to a strong Andreev conversion, giving rise to half-electron half-hole transmission through the junction structure, in sharp contrast to the suppression of Andreev conversion in the single chiral edge mode case. Our results suggest the importance of additional transport modes in the quantum anomalous Hall insulator-superconductor junction and will guide future transport measurements.

Interacting quantum many-body systems often generate exotic orders, either topological or conventional competing orders. Understanding these phases and the phase transitions between them are common issues in condensed-matter physics. How to characterize these states in a convincing and convenient way remains ambiguous. Here, we report our numerical study on the interacting $\nu =\frac{1}{2}$ hard-core boson system with topological flat bands based on the infinite density matrix group algorithm. We explicitly show that the entanglement spectral flow can be used to diagnose the quantum phases emerging in the hard-core boson systems. In particular, the subsequent charge pumping exhibits a linear, sinelike, and indiscernible dependence by the flux threading in the fractional Chern insulator, supersolid, and solid state, respectively. The real-space boson occupancy in the thermodynamic limit is further calculated for a better understanding of the respective state. We compare the phase diagram obtained here with that obtained by the previously exact diagonalization method, and qualitative differences are observed. Therefore, the infinite density matrix group algorithm provides a convincing and convenient way to study the phase transition in such a strongly correlated topological system.

Light-engineering of quantum materials via electromagnetic dressing is considered an on-demand approach for tailoring electronic band dispersions and even inducing topological phase transitions. For probing such dressed bands, photoemission spectroscopy is an ideal tool, and we employ here a novel experiment based on ultrafast photoemission momentum microscopy. Using this setup, we measure the in-plane momentum-dependent intensity fingerprints of the electromagnetically-dressed sidebands from a Au(111) surface for $s$- and $p$-polarized infrared driving. We find that at metal surfaces, due to screening of the driving laser, the contribution from Floquet-Bloch bands is negligible, and the dressed bands are dominated by the laser-assisted photoelectric effect. Also, we find, from calculations, that in contrast to general expectations, $s$-polarized light can dress free-electron states at large photoelectron momenta. Our results show that the dielectric response of the material must carefully be taken into account when using photoemission for the identification of light-engineered electronic band structures.

We report a neutron-scattering study on ${\mathrm{Pr}}_{2-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_4$ ($x\approx 0.5$) with magnetic incommensurability $\epsilon =0.461$ at 10 K, showing direct evidence for out-of-plane magnetic excitations caused by a non-negligible interlayer spin coupling ($J_{\perp }$). The magnetic spectrum is fully represented by linear spin wave theory considering an unconventional body-centered-like stacking of discommensurated spin stripes. A large easy-plane-type single-ion anisotropy ($\approx 1.5$ meV) has been found to be responsible for a finite-energy ($\approx 13$ meV) Goldstone mode at the magnetic zone center. Our results validate the presence of a sizable out-of-plane interaction resulting in an anisotropic three-dimensional nature of spin dynamics in ${\mathrm{Pr}}_{2-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_4$ near the half-doped region.

The multiscale entanglement renormalization ansatz (MERA) provides a constructive algorithm for realizing wave functions that are inherently scale invariant. Unlike conformally invariant partition functions, however, the finite bond dimension $\chi$ of the MERA provides a cutoff in the fields that can be realized. In this paper, we demonstrate that this cutoff is equivalent to the one obtained when approximating a thermal state of a critical Hamiltonian with a matrix product operator (MPO) of finite bond dimension $\chi$. This is achieved by constructing an explicit mapping between the isometries of the MERA and the local tensors of the MPO. In terms of energy scales, our results show that a finite bond dimension MERA is equivalent to introducing both an infrared and an ultraviolet scale, characterizing relevant and irrelevant perturbations on the underlying conformal field theory.

We investigate a textbook mixed-anion compound $\mathrm{Sr}{\mathrm{VO}}_2\mathrm{H}$ using first-principles calculation, to theoretically pin down the factors that stabilize its anion ordering. We find that the trans preference by the characteristic crystal field in the ${\mathrm{VO}}_4{\mathrm{H}}_2$ octahedron in addition to a coherent shrinkage along the V-H-V direction, taking place when such direction is consistent among neighboring hydrogens, stabilize the anion ordering observed in experiment. Our study gives an important clue for controlling the anion ordering in transition metal oxyhydrides.

In this work, we perform a combination of classical and spin wave analysis on the one-dimensional spin-$S$ Kitaev-Heisenberg-Gamma model in the region of an antiferromagnetic Kitaev coupling. Four phases are found, including a Néel ordered phase, a phase with $O_h\to D_3$ symmetry breaking, and “$D_3$-breaking I, II” phases which both break $D_3$ symmetries albeit in different ways, where $O_h$ is the full octahedral group and $D_3$ is the dihedral group of order six. The lowest-lying spin wave mass is calculated perturbatively in the vicinity of the hidden SU(2) symmetric ferromagnetic point.

A bilayer consisting of a ferrimagnetic insulator (FiM) and a heavy metal (HM) can be used as a “pump-probe” system to analyze the magnetic properties of the FiM. An oscillating electric current in the HM induces spin current injection into the FiM via the spin Hall effect. The resulting magnetization dynamics of the FiM, in turn, causes spin pumping back into the HM and modifies its conductivity via the inverse spin Hall effect (ISHE). We present a phenomenological theory to model the ISHE output spectrum, in which the Landau-Lifshitz-Gilbert equations governing the FiM dynamics are coupled to the spin-diffusion equations governing the spin and charge transports in the HM. It is found that the ISHE signal is greatly enhanced at the magnetization compensation point of the FiM. Furthermore, the peak frequencies and amplitudes of the ISHE spectrum are strongly correlated to the magnetic properties of the FiM sublattices. Most interestingly, the ISHE output can be increased by several orders of magnitude by tuning the on-site-sublattice and cross-sublattice damping constants. Our analysis shows the possibility of using the FiM/HM bilayer system as a sensitive probe into the magnetic parameters of the FiM sublattices. Conversely, the drastically enhanced ISHE signal with appropriate tuning of the damping parameters suggests a means to substantially improve the spin torque efficiency in FiM-based heterostructures.

Cofunctionality—the coexistence of different (possibly even contraindicated) properties in the same compound—is an exciting prospect that never fails to deliver interesting surprises, as in transparent while electrically conducting compounds, topological insulators having Rashba spin split bands, or electrically conducting while thermally insulating (thermoelectric) compounds. Here we study a cofunctionality of ferroelectricity and Rashba effect that combines the directional helical spin-polarization characteristic of the energy bands of bulk Rashba compounds with the existence of two opposite electric polarization states, characteristic of atomic displacements in displacive ferroelectrics. Flipping of the ferroelectric polarization (e.g., via an applied electric field) would result in the reversal of the Rashba spin polarization. However, thus far, only very few (essentially one) compounds have been found to be ferroelectric Rashba semiconductors (FERSCs), e.g., GeTe ($R3m$). In this paper, we propose a general strategy for the identification of compounds that possess cofunctionalities and apply it to perform an inverse design, finding compounds that simultaneously have ferroelectricity and Rashba spin splitting. The inverse design combining functionality $f_1$ with $f_2$ involves definition and utilization of causal factors that enable the said functionalities, and involves three steps: (1) screening materials that satisfy the enabling DPs common to the two functionalities $f_1$ and $f_2$; (2) filtering the materials according to DPs that are unique to each of the individual functionalities $f_1$ and $f_2$; and (3) by using the ensuing two compound lists of compounds $C\left(f_1\right)$ and $C\left(f_2\right)$ identifying the intersection between them, i.e., compounds $C\left(f_1,f_2\right)$ possessing simultaneous $f_1$ and $f_2$. Based on this process, we design 52 atomic combinations not suspected to be FERSCs that were previously synthesized. Of these 52 compounds, we find 24 FERSCs that are thermodynamically stable (i.e., reside on the convex hull) and, at the same time, feature larger spin splitting (large than 25 meV). These include ${\mathrm{BrF}}_5\left(Cmc{2}_1\right)$, $\mathrm{TlI}{\mathrm{O}}_3\left(R3m\right)$, $\mathrm{Zn}{\mathrm{I}}_2{\mathrm{O}}_6\left(P{2}_1\right)$, $\mathrm{LaTa}{\mathrm{O}}_4\left(Cmc{2}_1\right)$, ${\mathrm{Tl}}_3{\mathrm{S}}_3\mathrm{Sb}\left(R3m\right)$, ${\mathrm{Sn}}_2{\mathrm{P}}_2{\mathrm{Se}}_6$ (Pc), and ${\mathrm{Bi}}_2\mathrm{Si}{\mathrm{O}}_5\left(Cmc{2}_1\right)$ that have Rashba spin splitting of 31, 57, 111, 40, 90, 67, and 76 meV, respectively. Density functional theory calculations illustrate the reversal of the spin texture when the electric polarization is flipped. This paper validates a general approach for the search of other cofunctionalities based on causal enabling design principles rather than uncovering machine correlations.

In phononic crystals composed of solid inclusions distributed periodically in a fluid matrix, Bloch waves are a superposition of acoustic and elastic waves coupled at the boundaries of inclusions. Resonances internal to the unit cell and localized on the solid inclusions, when present, populate the phononic band structure with additional hybridization bands. Comparing the cases of nylon in water and of steel in water, that are conveniently accessible to experiment, we relate the hybridization bands to the resonant modes, also termed quasinormal modes, of a single solid inclusion immersed in water, that are identified numerically using a stochastic excitation technique. To characterize the hybridization of the resonant modes with the continuum of Bloch waves, we compute the complex phononic band structure giving evanescent Bloch waves with acoustoelastic coupling taken into account. In the particular case of hexagonal acoustoelastic phononic crystals, we observe that the acoustic Dirac cone centered at $K$ points of the first Brillouin zone can be severely affected without breaking the symmetry of the crystal.