We have carried out magnetization, heat-capacity, electrical, and magnetoresistance measurements (2–300 K) for the polycrystalline form of intermetallic compounds, $R_2\mathrm{RhS}{\mathrm{i}}_3(R=\mathrm{Gd}$, Tb, and Dy), forming in a $\mathrm{Al}{\mathrm{B}}_2$-derived hexagonal structure with a triangular $R$ network. This work was primarily motivated by a revival of interest on $\mathrm{G}{\mathrm{d}}_2\mathrm{PdS}{\mathrm{i}}_3$ after about two decades in the field of topological Hall effect due to magnetic skyrmions. We report here that these compounds are characterized by double antiferromagnetic transitions $(T_N=13.5$ and 12 K for Gd, 13.5 and 6.5 K for Tb, 6.5 and 2.5 K for Dy), but antiferromagnetism seems to be quite complex. The most notable observations common to all these compounds are as follows: (i) There are many features in the data mimicking those seen for $\mathrm{G}{\mathrm{d}}_2\mathrm{PdS}{\mathrm{i}}_3$, including the two magnetic transitions and the magnetic-field-induced changes in isothermal magnetization as though there are two metamagnetic transitions well below $T_N$. In view of such a resemblance of the properties, we speculate that these Rh-based materials offer a good playground to study topological Hall effect in a centrosymmetric structure, with its origin lying in triangular lattice of magnetic $R$ ions. (ii) There is an increasing contribution of electronic scattering with decreasing temperature towards $T_N$ in all cases, similar to $\mathrm{G}{\mathrm{d}}_2\mathrm{PdS}{\mathrm{i}}_3$, thereby serving as examples for a theoretical prediction for a classical spin-liquid phase in metallic magnetic systems due to geometrical frustration.

Dependence of transport coefficients of the $\mathrm{Yb}{\left({\mathrm{Rh}}_{1-x}{\mathrm{Co}}_x\right)}_2{\mathrm{Si}}_2$ series of alloys on temperature and cobalt concentration is explained by an asymmetric Anderson model which takes into account the exchange scattering of conduction electrons on ytterbium ions and the splitting of $4f$ states by the crystalline electric field (CEF). The substitution of rhodium by cobalt is described as an increase of chemical pressure which reduces the exchange coupling and the CEF splitting. The scaling analysis and numerical NCA solution of the model show that the effective degeneracy of the $4f$ state at a given temperature depends on the relative magnitude of the Kondo scale and the CEF splitting. Thus, we find that dependence of the thermopower, $S\left(T\right)$, on temperature and cobalt concentration can be understood as an interplay of quantum fluctuations, driven by the Kondo effect, and thermal fluctuations, which favor a uniform occupation of the CEF states. The theoretical model captures all the qualitative features of the experimental data and it explains the evolution of the shape of $S\left(T\right)$ with the increase of cobalt concentration.

We study the anisotropic spin-boson model (SBM) with the subohmic bath by a numerically exact method based on variational matrix product states. A rich phase diagram is found in the anisotropy-coupling strength plane by calculating several observables. There are three distinct quantum phases: a delocalized phase with even parity (phase I), a delocalized phase with odd parity (phase II), and a localized phase with broken $Z_2$ symmetry (phase III), which intersect at a quantum tricritical point. The competition between those phases gives an overall picture of the phase diagram. For small power of the spectral function of the bosonic bath, the quantum phase transition (QPT) from phase I to III with mean-field critical behavior is present, similar to the isotropic SBM. The phase diagram with three different phases can be found at large power of the spectral function: For the highly anisotropic case, the system experiences the QPTs from phase I to II via first order, and then to phase III via second order with the increase of the coupling strength. For the low anisotropic case, the system only experiences the continuous QPT from phase I to phase III with the non-mean-field critical exponents. Very interestingly, at the moderate anisotropy, the system would display the continuous QPTs for several times but with the same critical exponents. This unusual reentrance to the same localized phase is discovered in light-matter interacting systems. The present study on the anisotropic SBM could open an avenue to the rich quantum criticality.

First-principles density functional theory with the time-dependent Bethe-Salpeter Equation (BSE) is used to calculate the second harmonic generation (SHG) spectra of five trigonal prismatic ($2H$-phase) transition metal dichalcogenide (TMD) monolayers, $\mathrm{Mo}{\mathrm{S}}_2, \mathrm{MoS}{\mathrm{e}}_2, \mathrm{W}{\mathrm{S}}_2, \mathrm{WS}{\mathrm{e}}_2$, and $\mathrm{MoT}{\mathrm{e}}_2$, as a function of biaxial and uniaxial strain. It is shown that it is important to take excitonic effects into account when studying the effects of strain on SHG. All the TMDs exhibit very strong SHG, with hexagonal monolayer $\mathrm{MoT}{\mathrm{e}}_2$ dominating over the other TMDs in the 0.5–1.4 eV region. These results are shown to agree with experimental data. While $\mathrm{W}{\mathrm{S}}_2$ appears to be a good candidate for strain-tolerant applications because the SHG is insensitive to strain, $\mathrm{WS}{\mathrm{e}}_2$ exhibits a strong, consistent strain response that points to potential strain-sensitive applications. Distinct subpeaks of the $C$ exciton are observed which, when compared with the electronic structure, are attributed to specific transitions in the Brillouin zone, with the most important contributions coming from the $K\left(v_1{\to }_{}{c}_2\right),Q\left(v_1{\to }_{}{c}_1\right),$ and $\mathrm{\Gamma }(v_1\to c_1)$ points. These findings open avenues of exploration for potential applications of these materials in strain-sensitive devices and improve our understanding of the $C$ exciton in TMDs.

We show that H-phase transition metal dichalcogenide (TMD) monolayers, such as ${\mathrm{MoS}}_2$ and ${\mathrm{WSe}}_2$, are orbital Hall insulators. They present very large orbital Hall conductivity plateaus in their semiconducting gap, where the spin Hall conductivity vanishes. Our results open the possibility of using TMDs for orbital current injection and orbital torque transfers that surpass their spin-counterparts in spin-orbitronics devices. The orbital Hall effect in TMD monolayers occurs even in the absence of spin-orbit coupling. It can be linked to exotic momentum-space Dresselhaus-like orbital textures, analogous to the spin-momentum locking in two-dimensional Dirac fermions that arise from a combination of orbital attributes and lattice symmetry.

Using accurate first-principles calculations based on many-body perturbation theory, we predict that two-dimensional ${\mathrm{MoS}}_2$ hosts edge excitons with universal character, intrinsic to the existence of edges and lying well below the onset of bulk features. These excitons are largely insensitive to edge terminations or orientation, persisting even in the presence of metallic screening at zigzag edges, with large binding energies of $\sim 0.4$ eV. Additional excitons can also emerge in ultranarrow ribbons or as a function of the chemical nature of the termination. The chemical, structural, and electronic similarities with Se- or W-based transition-metal dichalcogenides suggest that these optical features could be common in this class of materials.

We have derived a method which allows us to compute the full and the Pauli reference kinetic potentials for atoms and molecules in a real-space representation. This is done by applying the optimized effective potential (OEP) method to the Kohn-Sham noninteracting kinetic energy expression. Additionally, we have also derived a simplified OEP variant based on the common energy denominator approximation which has proven to give much more stable and robust results than the original OEP. Moreover, we have also proved that at the solution point our approach is formally equivalent to the commonly used Bartolotti-Acharya formula.

We study theoretically the strong-field absorption of an ultrafast optical pulse by a gapped graphene monolayer. At low field amplitudes, the absorbance in pristine graphene is equal to the universal value of $2.3\%$. Although the ultrafast optical absorption for low field amplitudes is independent of the polarization, linear or circular, of the applied optical pulse, for high field amplitudes, the absorption strongly depends on the pulse polarization. For a linearly polarized pulse, the optical absorbance is saturated at the value of $\approx 1.4\%$ for the pulse's amplitude of $\ge 0.4\mathrm{V}/\AA$, but no such saturation is observed for a circularly polarized pulse. For the gapped graphene, the absorption of a linearly polarized pulse shows a weak dependence on the bandgap, while for a circularly polarized pulse, the absorption is very sensitive to the bandgap.

We report on broadband ferromagnetic resonance linewidth measurements performed on epitaxial Heusler thin films. A large and anisotropic two-magnon scattering linewidth broadening is observed for measurements with the magnetization lying in the film plane, while linewidth measurements with the magnetization saturated perpendicular to the sample plane reveal low Gilbert damping constants of $(1.5\pm 0.1)\times {10}^{-3}$, $(1.8\pm 0.2)\times {10}^{-3}$, and $<8\times {10}^{-4}$ for ${\mathrm{Co}}_2\mathrm{MnSi}/\mathrm{MgO}$, ${\mathrm{Co}}_2\mathrm{MnAl}/\mathrm{MgO}$, and ${\mathrm{Co}}_2\mathrm{FeAl}/\mathrm{MgO}$, respectively. The in-plane measurements are fit to a model combining Gilbert and two-magnon scattering contributions to the linewidth, revealing a characteristic disorder length scale of 10–100 nm.

We show by direct numerical simulations that the turbulence generated by steadily heating a long cylinder immersed in helium II is strongly inhomogeneous and consists of a dense turbulent layer of quantized vortices localized around the cylinder. We analyze the properties of this superfluid turbulence in terms of radial distribution of the vortex line density and the anisotropy and we compare these properties to the better-known properties of homogeneous counterflow turbulence in channels.

We study the time evolution of the cloud of Dy atoms dispersed in superfluid helium and investigate the possibility of using these atoms as tracers for the imaging of superfluid-helium flows. The atoms are produced by pulsed laser ablation and are visualized via their laser-induced fluorescence. It turns out that the observation time is limited by the optical pumping of the atomic population into a nonabsorbing metastable state which is also responsible for the saturation of the fluorescence yield observed earlier.

We explore the relation between the entanglement of a pure state and its energy variance for a local one-dimensional Hamiltonian, as the system size increases. In particular, we introduce a construction which creates a matrix product state of arbitrarily small energy variance ${\delta }^2$ for $N$ spins, with bond dimension scaling as $\sqrt{N}{D}_0^{1/\delta }$, where $D_0>1$ is a constant. This implies that a polynomially increasing bond dimension is enough to construct states with energy variance that vanishes with the inverse of the logarithm of the system size. We run numerical simulations to probe the construction on two different models and compare the local reduced density matrices of the resulting states to the corresponding thermal equilibrium. Our results suggest that the spatially homogeneous states with logarithmically decreasing variance, which can be constructed efficiently, do converge to the thermal equilibrium in the thermodynamic limit, while the same is not true if the variance remains constant.

We performed neutron diffraction experiments on a single crystal of an $S=\frac{1}{2}$ frustrated ferromagnetic chain compound ${\mathrm{NaCuMoO}}_4$(OH) at zero and finite magnetic fields. Three magnetic Bragg peaks with the propagation vector of $\mathit{q}=(0,\delta ,0)$ $[\delta =0.481(1\left)\right]$ were observed at the zero field, which means that an incommensurate helical magnetic order was realized. Using the ratio of the intensities between these magnetic peaks, a proper-screw structure was suggested, where the spiral plane is the crystallographic $ac$ plane. While the $\delta$ is unchanged at lower fields, it decreases linearly with the field where ${\mu }_{0}H\ge 2.5\mathrm{T}$. The field dependence is consistent with that of the field-induced spin density wave state that originated from the formation of the bound state of two magnons in the $S=\frac{1}{2}$ frustrated ferromagnetic chain.

By using a microscopic dipole-exchange theory within a Green's function formalism, we study the coupling regime of microwave cavity photons to magnons in nanostructures. The ferromagnetic nanostructures considered are single- and double-layer films, nanowires with rectangular cross-sections, and one-dimensional magnonic crystal arrays of nanowires. In contrast with previous studies of magnon-photon hybrid systems, where either bulklike magnetic samples or macroscopic spheres or films were utilized, a discrete lattice of effective spins is employed to establish a microscopic theory for describing the dependence of the magnon frequencies on the wave vector. We explore hybrid systems derived from the discrete magnons in nanostructures and a selected microwave cavity photon, where strong photon-magnon coupling is expected. This may extend the functionality of the existing hybrid systems or may introduce new functionality. The dependence of the hybridized frequency modes on applied magnetic field are calculated and it is shown that the results are significantly modified compared with those for magnetic bulk materials. In particular, a series of anticrossing phenomena of the cavity mode and multiple magnon modes of ferromagnetic nanostructures are reported. Our findings are important for future applications in integrated hybrid systems for quantum magnonics.

Rhenium based noncentrosymmetric superconductors crystallizing in $\alpha$-Mn structure have become potential candidates to exhibit an unconventional superconducting ground state. Here we report a detailed investigation on the superconducting and normal state properties of ${\mathrm{Re}}_{5.5}\mathrm{Ta}$, that also has the $\alpha$-Mn structure. Magnetization, specific heat, and transport measurements confirm the bulk superconducting transition $T_C$ at 8.0 K. Upper critical field value [$H_{C2}\left(0\right)$] calculated from magnetization, specific heat, and AC transport measurements exceed the Pauli paramagnetic limit (14.7 T), indicating that the superconducting properties of ${\mathrm{Re}}_{5.5}\mathrm{Ta}$ are probably unconventional in nature. However, low-temperature specific heat and transverse-field muon spin rotation measurements suggest a surprising nodeless isotropic superconducting gap, although with strong electron-phonon coupling.

We report here a giant $\left|{\chi }_{baa}^{\left(2\right)}\right|=780$ pm/V second harmonic and $\left|{\chi }_{aaaa}^{\left(3\right)}\right|=1.4\times {10}^{-17}{\mathrm{m}}^2/{\mathrm{V}}^2$ third harmonic signal from single atomic sheet of buckled hexagonal GaAs. We demonstrate this through the solution of an ab initio real-time Bethe-Salpeter equation by including the electron-hole screened-exchange self-energy. The coupling between time-dependent external electric field and correlated electrons is treated within the modern theory of polarization. The result of our calculation envisage monolayer GaAs to be a prominent member in the material library for nonlinear signal generations.

In order to explore the physical properties of orthorhombic ${\mathrm{U}}_2\mathrm{C}{\mathrm{o}}_3\mathrm{S}{\mathrm{i}}_5$-type $\mathrm{S}{\mathrm{m}}_2\mathrm{R}{\mathrm{u}}_3\mathrm{G}{\mathrm{e}}_5$, we have carried out a combined study by means of the measurements of the magnetic susceptibility χ, electrical resistivity ρ, Seebeck coefficient S, and specific heat $C_p$. An antiferromagnetic phase transition at the Néel temperature $T_N\simeq 7\mathrm{K}$ has been identified by all measured physical quantities. Remarkably, another intrinsic phase transition characterized by marked features has been discerned at $T^{*}\simeq 240\mathrm{K}$. The distinct peak in $C_p$ at $T^{*}$ with the lack of thermal hysteresis behavior provides strong evidence for the second-order phase transition in nature. It is noticed that the observations near $T^{*}$ are reminiscent of a typical charge density wave (CDW) ordering. We compared the experimental results with those observed in a polymorph of $\mathrm{S}{\mathrm{m}}_2\mathrm{R}{\mathrm{u}}_3\mathrm{G}{\mathrm{e}}_5$ with the tetragonal $\mathrm{S}{\mathrm{c}}_2\mathrm{F}{\mathrm{e}}_3\mathrm{S}{\mathrm{i}}_5$-type structure which was recently reported to exhibit the coexistence of magnetic and CDW phase transitions. On this basis, the observed features in orthorhombic $\mathrm{S}{\mathrm{m}}_2\mathrm{R}{\mathrm{u}}_3\mathrm{G}{\mathrm{e}}_5$ have been discussed by comparing with the results in tetragonal $\mathrm{S}{\mathrm{m}}_2\mathrm{R}{\mathrm{u}}_3\mathrm{G}{\mathrm{e}}_5$ as well as other CDW systems.

We investigate the spin-1/2 Heisenberg antiferromagnet on a kagome lattice with breathing anisotropy (i.e., with weak and strong triangular units), constructing an improved simplex resonating valence bond (RVB) ansatz by successive applications (up to three times) of local quantum gates, which implement a filtering operation on the bare nearest-neighbor RVB state. The resulting projected entangled pair state involves a small number of variational parameters (only one at each level of application) and preserves full lattice and spin-rotation symmetries. Despite its simple analytic form, the simplex RVB provides very good variational energies at strong and even intermediate breathing anisotropy. We show that it carries ${\mathbb{Z}}_2$ topological order which does not fade away under the first few applications of the quantum gates, suggesting that the RVB topological spin liquid becomes a competing ground state candidate for the kagome antiferromagnet at large breathing anisotropy.