The noncentrosymmetric superconductor ${\mathrm{Re}}_6\mathrm{Zr}$ has attracted much interest for its possible unconventional superconducting state with broken time-reversal symmetry. Here we report ${}^{185/187}\mathrm{Re}$ nuclear quadrupole resonance measurements on ${\mathrm{Re}}_6\mathrm{Zr}$ $(T_c=6.72$ K) and the isostructural compounds ${\mathrm{Re}}_{27}{\mathrm{Zr}}_5$ $(T_c=6.53$ K) and ${\mathrm{Re}}_{24}{\mathrm{Zr}}_5$ $(T_c=5.00$ K). The nuclear spin-lattice relaxation rate $1/T_1$ shows a coherence peak below $T_c$ and decreases exponentially at low temperatures in all three samples. The superconducting gap $\mathrm{\Delta }$ derived from the $1/T_1$ data is $2\mathrm{\Delta }=3.58k_B{T}_c,3.55k_B{T}_c$, and $3.51k_B{T}_c$ for ${\mathrm{Re}}_6\mathrm{Zr},{\mathrm{Re}}_{27}{\mathrm{Zr}}_5$, and ${\mathrm{Re}}_{24}{\mathrm{Zr}}_5$, respectively, which is close to the value of $3.53k_B{T}_c$ expected for weak-coupling superconductivity. These data suggest conventional $s\text{-wave}$ superconductivity with a fully opened gap in this series of compounds.

In this work we propose and explore an effective numerical approach for investigation of critical current dependence on applied magnetic field for magnetic Josephson junctions with in-plane magnetization orientation. This approach is based on micromagnetic simulation of the magnetization reversal process in the ferromagnetic layer with introduced internal magnetic stiffness and subsequent reconstruction of the critical current value using total flux or reconstructed actual phase difference distribution. The approach is flexible and shows good agreement with experimental data obtained on Josephson junctions with ferromagnetic barriers. Based on this approach we have obtained a critical current dependence on applied magnetic field for rectangular magnetic Josephson junctions with high size aspect ratio. We have shown that the rectangular magnetic Josephson junctions can be considered for application as an effective Josephson magnetic memory element with the value of critical current defined by the orientation of magnetic moment at zero magnetic field. An impact of shape magnetic anisotropy on critical current is revealed and discussed. Finally, we have considered a curling magnetic state in the ferromagnetic layer and demonstrated its impact on critical current.

In the framework of a multiorbital Hubbard model description of superconductivity, a matrix formulation of the superconducting pairing interaction that has been widely used is designed to treat spin, charge, and orbital fluctuations within a random phase approximation (RPA). In terms of Feynman diagrams, this takes into account particle-hole ladder and bubble contributions as expected. It turns out, however, that this matrix formulation also generates additional terms which have the diagrammatic structure of vertex corrections. Here we examine these terms and discuss the relationship between the matrix-RPA superconducting pairing interaction and the Feynman diagrams that it sums.

A domain wall and spin supercurrent can coexist in magnets with easy-cone anisotropy owing to simultaneous spontaneous breaking of $Z_2$ and U(1) symmetries. Their interaction is theoretically investigated in quasi-one-dimensional ferromagnets within the Landau-Lifshitz-Gilbert phenomenology. Specifically, the spin supercurrent can exert the torque on a domain wall and thereby drive it. We also show, as a reciprocal phenomenon, a field-induced motion of a domain wall can generate spin supercurrent.

We performed terahertz time-domain spectroscopy, low-frequency Raman scattering, and Brillouin light scattering on vitreous glucose to investigate the boson peak (BP) dynamics. In the spectra of $\alpha \left(\nu \right)/{\nu }^2$ $\mathrm{[}\alpha \left(\nu \right)$ is the absorption coefficient], the BP is clearly observed around 1.1 THz. Correspondingly, the complex dielectric constant spectra show a universal resonancelike behavior only below the BP frequency. As an analytical scheme, we propose the relative light-vibration coupling coefficient (RCC), which is obtainable from the combination of the far-infrared and Raman spectra. The RCC reveals that the infrared light-vibration coupling coefficient $C_{\mathrm{IR}}\left(\nu \right)$ of the vitreous glucose behaves linearly on frequency which deviates from Taraskin's model of $C_{\mathrm{IR}}\left(\nu \right)=A+B{\nu }^2$ [S. N. Taraskin et al., Phys. Rev. Lett. 97, 055504 (2006)]. The linearity of $C_{\mathrm{IR}}\left(\nu \right)$ might require modification of the second term of the model. The measured transverse sound velocity shows an apparent discontinuity with the flattened mode observed in the inelastic neutron scattering study [N. Violini et al., Phys. Rev. B 85, 134204 (2012)] and suggests a coupling between the transverse acoustic and flattened modes.

The nonlocal coherent-potential approximation provides a systematic technique for the study of short-range ordering effects in a variety of disordered systems. In its original formulation the technique, however, shows an unwanted dependence on details in the coarse-grained effective medium construction. This is particularly evident in the study of $\vec{k}$-resolved quantities, such as the Bloch spectral function and other non-site-diagonal observables. We remove the issue and recover fully physical results in first principles studies of real materials, by means of a resampling procedure first proposed for model tight-binding Hamiltonians. The prescription is further generalized to the case of complex unit cell compounds, with more than a single sublattice, and illustrated through examples from metallic alloys and disordered local moment simulations of paramagnetism in the prototype iron-based superconductor FeSe.

We calculate and present an analytic form of the magneto-optical conductivity for the gapped low-energy Kane model in two and three dimensions separately. The two-dimensional case maps onto the $\alpha \text{−}{\mathcal{T}}_3$ model at a particular value of $\alpha =1/\sqrt{3}$. In two dimensions, two chiral sectors exist, between which there are no optically activated transitions. In three dimensions, the extra dimension of dispersion mixes the two sectors so that intra- and intersector transitions can occur. The latter type of transition can be separated out via circular polarizations of light, and it shows a distinct signature in the transverse conductivity.

Rashba spin-orbit interaction leads to a number of electromagnetic cross-correlation effects by inducing a mixing of electric and magnetic degrees of freedom. In this study, we investigate the optical properties of a magnetic Rashba conductor by deriving an effective Hamiltonian based on an imaginary-time path-integral formalism. We show that the effective Hamiltonian can be described in terms of toroidal and quadrupole moments, as has been argued in the case of insulator multiferroics. The toroidal moment turns out to coincide with the spin gauge field induced by the Rashba field. It causes Doppler shift by inducing intrinsic spin current, resulting in anisotropic light propagation (directional dichroism) irrespective of the polarization. The quadrupole moment on the other hand results in a magneto-optical phenomenon such as a Faraday effect for circularly polarized waves.

The ever increasing level of control in the fabrication of graphene/hexagonal boron nitride ($h$-BN) lateral heterostructures makes it promising for material realization of exotic electronic and spintronic properties of graphene. Yet recent first-principles studies have revealed that the pronounced half-metallicity expected for electrically biased freestanding graphene nanoribbons is severely suppressed when the lateral heterostructures are orientationally aligned. By properly tailoring the orientational misalignment between zigzag graphene and chiral $h$-BN nanoribbons, here we show that the half-metallicity can be substantially enhanced from the aligned case, back to be comparable in magnitude with the freestanding case. In addition, the strain energy accumulation in such misaligned heterojunctions is significantly diminished, favoring physical realization of such structures. The restored half-metallicity is largely attributed to the recovered superexchange interaction between the electrons at the opposite heterojunction interfaces. The present findings may have important implications in the development of graphene-based spintronics.

Tunneling between a point contact and a one-dimensional wire is usually described with the help of a tunneling Hamiltonian that contains a $\delta$ function in position space. Whereas the leading-order contribution to the tunneling current is independent of the way this $\delta$ function is regularized, higher-order corrections with respect to the tunneling amplitude are known to depend on the regularization. Instead of regularizing the $\delta$ function in the tunneling Hamiltonian, one may also obtain a finite tunneling current by invoking the ultraviolet cutoffs in a field-theoretic description of the electrons in the one-dimensional conductor, a procedure that is often used in the literature. For the latter case, we show that standard ultraviolet cutoffs lead to different results for the tunneling current in fermionic and bosonized formulations of the theory, when going beyond leading order in the tunneling amplitude. We show how to recover the standard fermionic result using the formalism of functional bosonization and revisit the tunneling current to leading order in the interacting case.

The elastic dipole tensor is a fundamental quantity relating the elastic field and atomic structure of a point defect. We review three methods in the literature to calculate the dipole tensor and apply them to hydrogen in $\alpha$-zirconium using density functional theory (DFT). The results are compared with the dipole tensor deduced from earlier experimental measurements of the $\lambda$ tensor for hydrogen in $\alpha$-zirconium. There are significant errors with all three methods. We show that calculation of the $\lambda$ tensor, in combination with experimentally measured elastic constants and lattice parameters, yields dipole tensor components that differ from experimental values by only 10%–20%. There is evidence to suggest that current state-of-the-art DFT calculations underestimate bonding between hydrogen and $\alpha$-zirconium.

In systems where electrons form both dispersive bands and small local spins, we show that changes in the spin configuration can tune the bands through a Lifshitz transition, resulting in a continuous metal-insulator transition associated with a progressive change in the Fermi surface topology. In contrast to the Mott-Hubbard and Slater pictures, this spin-driven Lifshitz transition appears in systems with a small electron-electron correlation and large hybridization. We show that this situation is realized in $5d$ distorted perovskites with half-filled $t_{2g}$ bands such as ${\mathrm{NaOsO}}_3$, where the strong $p-d$ hybridization reduces the local moment, and spin-orbit coupling causes a large renormalization of the electronic mobility. This weakens the role of electronic correlations and drives the system towards an itinerant magnetic regime which enables spin fluctuations.

We use first-principles calculations to investigate the band structure evolution of $\mathrm{W}{X}_2$/$\mathrm{Mo}{X}_2$ ($X$ = S, Se) heterobilayers under a perpendicular electric field. We characterize the extent to which the type II band alignment in these compounds can be tuned or inverted electrostatically. Our results demonstrate two effects of the stacking configuration. First, different stackings produce different net dipole moments, resulting in band offset variations that are larger than 0.1 eV. Second, based on symmetry constraints that depend on stacking, a perpendicular electric field may hybridize $\mathrm{W}{X}_2$ and $\mathrm{Mo}{X}_2$ bands that cross at the Brillouin zone corner $K$. Our results suggest that external electric fields can be used to tune the physics of intralayer and interlayer excitons in heterobilayers of transition metal dichalcogenides.

We use the density-matrix renormalization group, applied to a one-dimensional model of continuum Hamiltonians, to accurately solve chains of hydrogen atoms of various separations and numbers of atoms. We train and test a machine-learned approximation to $F\left[n\right]$, the universal part of the electronic density functional, to within quantum chemical accuracy. We also develop a data-driven, atom-centered basis set for densities which greatly reduces the computational cost and accurately represents the physical information in the machine-learning calculation. Our calculation (a) bypasses the standard Kohn-Sham approach, avoiding the need to find orbitals, (b) includes the strong correlation of highly stretched bonds without any specific difficulty (unlike all standard DFT approximations), and (c) is so accurate that it can be used to find the energy in the thermodynamic limit to quantum chemical accuracy.

Measurements of the electric resistivity $\rho \left(T\right)$ under pressure up to 8 GPa were performed on high-quality single crystals of the Yb-based heavy-fermion system $\beta -{\mathrm{YbAlB}}_4$ in the temperature range $2<T<300$ K. In the resistivity data, we observed pressure-induced magnetic ordering above the critical pressure $P_{\mathrm{c}}\sim 2$ GPa. The clear difference in the phase diagram under pressure using two types of pressure media indicates that the transition temperature may be further enhanced under application of uniaxial pressure. With pressure, this phase-transition temperature $T_{\mathrm{M}}$ is enhanced, reaching 32 K at 8 GPa, which is the highest transition temperature so far recorded for the Yb-based heavy-fermion compounds. The power-law exponent $\alpha$ in $\rho ={\rho }_0+A{T}^{\alpha }$ below $T_{\mathrm{M}}$ gradually changes from 3/2 to 5/2 with increasing pressure from 2 to 8 GPa. In contrast, the resistivity exhibits a $T$-linear behavior in the temperature range $2\le T\le 20$ K and is insensitive to pressure below $P_{\mathrm{c}}$. In this pressure regime, the magnetization is also nearly independent of pressure and shows no anomaly above 2 K. Our results indicate that a quantum critical point for $\beta -{\mathrm{YbAlB}}_4$ is also located near $P_{\mathrm{c}}$ in addition to the strange metal region near the ambient pressure.

The eigenstate thermalization hypothesis conjectures that for a thermodynamically large system in one of its energy eigenstates, the reduced density matrix describing any finite subsystem is determined solely by a set of relevant conserved quantities. In a chaotic quantum system, only the energy is expected to play that role and hence eigenstates appear locally thermal. Integrable systems, on the other hand, possess an extensive number of such conserved quantities and therefore the reduced density matrix requires specification of all the corresponding parameters (generalized Gibbs ensemble). However, here we show by unbiased statistical sampling of the individual eigenstates with a given finite energy density that the local description of an overwhelming majority of these states of even such an integrable system is actually Gibbs-like, i.e., requires only the energy density of the eigenstate. Rare eigenstates that cannot be represented by the Gibbs ensemble can also be sampled efficiently by our method and their local properties are then shown to be described by appropriately truncated generalized Gibbs ensembles. We further show that the presence of these rare eigenstates differentiates the model from the chaotic case and leads to the system being described by a generalized Gibbs ensemble at long time under a unitary dynamics following a sudden quench, even when the initial state is a typical (Gibbs-like) eigenstate of the prequench Hamiltonian.

The excitation of plasmonic gold nanoparticles by ultrashort laser pulses can trigger interesting electron-based effects in biological media such as production of reactive oxygen species or cell membrane optoporation. In order to better understand the optical and thermal processes at play, we modeled the interaction of a subpicosecond, near-infrared laser pulse with a gold nanorod in water. A nonthermal model is used and compared to a simple two-temperature thermal approach. For both models, the computation of the transient optical response reveals strong plasmon damping. Electron emission from the metal into the water is also calculated in a specific way for each model. The dynamics of the resulting local plasma in water is assessed by a rate equation model. While both approaches provide similar results for the transient optical properties, the simple thermal one is unable to properly describe electron emission and plasma generation. The latter is shown to mostly originate from electron-electron thermionic emission and photoemission from the metal. Taking into account the transient optical response is mandatory to properly calculate both electron emission and local plasma dynamics in water.

The lacunar spinel $\mathrm{Ge}{\mathrm{V}}_4{\mathrm{S}}_8$ undergoes orbital and ferroelectric ordering at the Jahn-Teller transition around 30 K and exhibits antiferromagnetic order below about 14 K. In addition to this orbitally driven ferroelectricity, lacunar spinels are an interesting material class, as the vanadium ions form ${\mathrm{V}}_4$ clusters representing stable molecular entities with a common electron distribution and a well-defined level scheme of molecular states resulting in a unique spin state per ${\mathrm{V}}_4$ molecule. Here we report detailed x-ray, magnetic susceptibility, electrical resistivity, heat capacity, thermal expansion, and dielectric results to characterize the structural, electric, dielectric, magnetic, and thermodynamic properties of this interesting material, which also exhibits strong electronic correlations. From the magnetic susceptibility, we determine a negative Curie-Weiss temperature, indicative for antiferromagnetic exchange and a paramagnetic moment close to a spin $S=1$ of the ${\mathrm{V}}_4$ molecular clusters. The low-temperature heat capacity provides experimental evidence for gapped magnon excitations. From the entropy release, we conclude about strong correlations between magnetic order and lattice distortions. In addition, the observed anomalies at the phase transitions also indicate strong coupling between structural and electronic degrees of freedom. Utilizing dielectric spectroscopy, we find the onset of significant dispersion effects at the polar Jahn-Teller transition. The dispersion becomes fully suppressed again with the onset of spin order. In addition, the temperature dependencies of dielectric constant and specific heat possibly indicate a sequential appearance of orbital and polar order.

Static spin-stripe order and superconductivity were systematically studied in ${\mathrm{La}}_{2-x}{\mathrm{Ba}}_x{\mathrm{CuO}}_4$ $\left(0.11\le x\le 0.17\right)$ at ambient pressure by means of magnetization and $\mu \mathrm{SR}$ experiments. We find that all the investigated ${\mathrm{La}}_{2-x}{\mathrm{Ba}}_x{\mathrm{CuO}}_4$ samples exhibit static spin-stripe order and that the quasi-two-dimensional superconducting (SC) transition temperature $T_{\mathrm{c}1}$ and the static spin-stripe order temperature $T_{\mathrm{so}}$ have very similar values throughout the phase diagram. Moreover, the magnetic and the SC properties of the $x=0.155$ (LBCO-0.155) and $x=0.17$ (LBCO-0.17) samples were studied under hydrostatic pressure. As a remarkable result, in these bulk cuprate superconductors, the three-dimensional SC transition temperature $T_{\mathrm{c}}$ and $T_{\mathrm{so}}$ nearly coincide $[T_{\mathrm{c}}\left(p\right)\simeq T_{\mathrm{so}}\left(p\right)]$ at all pressure investigated $(0\le p\le 2.3$ GPa). We also observed a pressure induced transition from long-range spin stripe order to a disordered magnetic state at $p^{☆}\simeq 1.6$ GPa in LBCO-0.155, coexisting with a SC state with substantial superfluid density. In LBCO-0.17, a disordered magnetic state is present at all $p$. The present results indicate that static magnetic order and SC pairing correlations develop in a cooperative fashion in ${\mathrm{La}}_{2-x}{\mathrm{Ba}}_x{\mathrm{CuO}}_4$, and provide a new route of understanding the complex interplay between static magnetism and superconductivity in the stripe phase of cuprates.

There is increasing body of experimental evidences of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in quasi-low-dimensional organic and heavy-fermion superconductors. The emergence of the FFLO phase has been demonstrated mainly based on a thermodynamic quantity or microscopically with spin polarization distribution that exhibit anomalies within the superconducting state in the presence of the in-plane magnetic field. However, the direct observation of superconducting order parameter modulation is so far (still) missing. Within the quasiclassical approach and Ginzburg-Landau formalism we study how the orbital effect of the in-plane field influences the FFLO instability in quasi-one-dimensional superconductors with a sufficiently weak interlayer coupling locking the magnetic flux to Josephson-type vortices. By making use of the continuum limit approximation of the Frenkel-Kontorova model for competing periodicities, we find and characterize the locking behavior of the modulation wave vector, when it remains equal to the magnetic length through some range of values of the external field.