We respond to the Comment by Pushkarov. We find that, in solid ${}^4\mathrm{He}, {}^3\mathrm{He}$ impurity atoms that pin dislocation segments are not impuritons, but randomly walking particles. The interpretation for the rotation effect, which was based on the impuriton model, does have to be totally reconsidered, taking into account the motion of randomly walking ${}^3\mathrm{He}$ in the strong elastic potential near the core of edge dislocations.

We show that the gap parameter in semi-Dirac material induces a large degree of sensitivity for interband optical conductivity with respect to the polarization direction. The optical conductivity reveals an abruptly large value at a certain frequency for light along a particular polarization direction while it is significantly suppressed along the direction orthogonal to the former. The direction-dependent optical conductivity may, in turn, be used to uniquely predict the dispersive nature of the two-dimensional semi-Dirac materials, in addition to other possible applications in the field of transparent conductors.

We theoretically study coherent multiple Andreev reflections in a biased three-terminal Josephson junction. We demonstrate that the direct current flowing through the junction consists of supercurrent components when the bias voltages are commensurate. This dissipationless current depends on the phase in the superconducting leads and stems from the Cooper pair transfer processes induced by nonlocal Andreev reflections of the quasiparticles originating from the superconducting leads. We identify supercurrent-enhanced lines in the current and conductance maps of the recent measurement [PNAS 115, 6991 (2018)] on a nanowire Josephson junction and show that the magnitude of the phase-dependent current components is proportional to the junction transparency with the power corresponding to the component order.

We show that the $N$-patch functional renormalization group (pFRG), a theoretical method commonly applied to correlated electron systems, is unable to implement consistently the matrix element interference arising from strong momentum dependence in the Bloch state contents or the interaction vertices. We show that such a deficit could lead to results incompatible with the checkable limits of weak and strong coupling. We propose that the pFRG could be improved by better accounting for momentum conservation.

Kondo-based semimetals and semiconductors are of extensive current interest as a viable platform for strongly correlated states in the dilute carrier limit. It is thus important to explore the routes to understand such systems. One established pathway is through the Kondo effect in metallic nonmagnetic analogs, in the so called half-filling case of one conduction electron and one $4f$ electron per site. Here, we demonstrate that Kondo-based semimetals develop out of conduction electrons with a low-carrier density in the presence of an even number of rare-earth sites. We do so by studying the Kondo material ${\mathrm{Yb}}_3{\mathrm{Ir}}_4{\mathrm{Ge}}_{13}$ along with its closed-$4f$-shell counterpart, ${\mathrm{Lu}}_3{\mathrm{Ir}}_4{\mathrm{Ge}}_{13}$. Through magnetotransport, optical conductivity, and thermodynamic measurements, we establish that the correlated semimetallic state of ${\mathrm{Yb}}_3{\mathrm{Ir}}_4{\mathrm{Ge}}_{13}$ below its Kondo temperature originates from the Kondo effect of a low-carrier conduction-electron background. In addition, it displays fragile magnetism at very low temperatures, which in turn, can be tuned to a Griffiths-phase-like regime through Lu-for-Yb substitution. These findings are connected with recent theoretical studies in simplified models. Our results can pave the way to exploring strong correlation physics in a semimetallic environment.

We present and motivate an efficient way to include orbital-dependent many-body correlations in trial wave functions of real-space quantum Monte Carlo methods for use in electronic structure calculations. We apply our new orbital-dependent backflow wave function to calculate ground state energies of the first row atoms using variational and diffusion Monte Carlo methods. The systematic overall gain of correlation energy with respect to single determinant Jastrow-Slater wave functions is competitive with the best single determinant trial wave functions currently available. The computational cost per Monte Carlo step is comparable to that of simple backflow calculations.

We present exact results for the susceptibility of the interacting resonant level model in equilibrium. Detailed simulations using both the numerical renormalization group and density matrix renormalization group were performed in order to compare with closed analytical expressions. By first bosonizing the model and then utilizing the integrability of the resulting boundary sine-Gordon model, one finds an analytic expression for the relevant energy scale $T_K$ with excellent agreement to the numerical results. On the other hand, direct application of the Bethe ansatz of the interacting resonant level mode does not correctly reproduce $T_K$—however, if the bare parameters in the model are renormalized, then quantities obtained via the direct Bethe ansatz such as the occupation of the resonant level as a function of the local chemical potential do match the numerical results. The case of one lead is studied in the most detail, with many results also extending to multiple leads, although there still remain open questions in this case.

We report the transport properties of bilayer graphene (BLG) due to the increase of Coulomb potential fluctuations and the decrease of K adatom concentration $\left({\mathrm{n}}_{\mathrm{K}}\right)$ induced by diffusion and cluster formation of the K adatom as a function of temperature (20–300 K) and time at room temperature (RT). Upon K adatom deposition on BLG at $T=20$ K, conductivity decreased due to the emergence of Coulomb scatterers, and the dependence of conductivity transformed from linear $\left(\sigma \sim n^{\alpha },\alpha \sim 1\right)$ to superlinear $\left(\alpha \sim 1.5\right)$. As the inhomogeneity of the Coulomb potential on BLG increased by cluster formation of K adatoms, the magnitude of the conductivity increased, and the dependence of conductivity on charge carrier density (curvature) shifted towards linear behavior. We fit the experimental data with Boltzmann transport theory to show that the changes in the transport properties of BLG in the presence of charged impurities originate from two factors, ${\mathrm{n}}_{\mathrm{K}}$ and the Thomas-Fermi screening vector $\left({\mathrm{q}}_{\mathrm{TF}}\right)$, which are both affected by cluster formation of K adatoms on BLG and the subsequent increase of Coulomb potential inhomogeneity.

The chiral edge state (CES) at zero magnetic field has already been realized in the magnetically doped topological insulator (TI). However, this scheme strongly relies on material breakthroughs, and in fact, most of the TIs cannot be driven into a Chern insulator in this way. Here, we propose to achieve the CESs in two-dimensional TI/ferromagnetic insulator/TI sandwiched structures through spin-selective coupling between the helical edge states of the two TIs. Due to this coupling, the edge states of one spin channel are gapped and those of the other spin channel remain almost gapless, so that the helical edge states of each isolated TI are changed into the CESs. Such CESs can be hopefully achieved in all TI materials, which are immune to magnetic-disorder-induced backscattering. We propose to implement our scheme in the van der Waals heterostructures between monolayer $1T^{\prime }\text{−}{\mathrm{WTe}}_2$ and bilayer ${\mathrm{CrI}}_3$. The electrical control of magnetism in bilayer ${\mathrm{CrI}}_3$ switches the transport direction of the CESs, which can realize a low-consumption transistor.

The Kelvin-Helmholtz instability is well known in classical hydrodynamics where it explains the sudden emergence of interfacial surface waves as a function of the flow velocity parallel to the interface. It can be carried over to the inviscid two-fluid dynamics of superfluids, to describe the stability of the phase boundary separating two bulk phases of superfluid ${}^3\mathrm{He}$ in rotating flow when the boundary is localized with a magnetic-field gradient. The results from extensive measurements as a function of temperature and pressure confirm that in the superfluid the classic condition for stability is changed and that the magnetic polarization of the $B$ phase at the phase boundary has to be taken into account, which yields the magnetic-field-dependent interfacial surface tension.

In most lattice models, the closing of a band gap typically occurs at high-symmetry points in the Brillouin zone. Differently, in the Creutz model—describing a system of spinless fermions hopping on a two-leg ladder pierced by a magnetic field—the gap closing at the quantum phase transition between the two topologically nontrivial phases of the model can be moved by tuning the hopping amplitudes. We take advantage of this property to examine the nonequilibrium dynamics of the model after a sudden quench of the magnetic flux through the plaquettes of the ladder. For a quench to one of the equilibrium quantum critical points, we find that the revival period of the Loschmidt echo—measuring the overlap between initial and time-evolved states—is controlled by the gap closing zero-energy modes. In particular, and contrary to expectations, the revival period of the Loschmidt echo for a finite ladder does not scale linearly with size but exhibits jumps determined by the presence or absence of zero-energy modes. We further investigate the conditions for the appearance of dynamical quantum phase transitions in the model and find that, for a quench to an equilibrium critical point, such transitions occur only for ladders of sizes which host zero-energy modes. Exploiting concepts from quantum thermodynamics, we show that the average work and the irreversible work per lattice site exhibit a weak dependence on the size of the system after a quench across an equilibrium critical point, suggesting that quenching into a different phase induces effective correlations among the particles.

Thermal properties of molybdenum disulfide $\left({\mathrm{MoS}}_2\right)$ have recently attracted attention related to fundamentals of heat propagation in strongly anisotropic materials, and in the context of potential applications to optoelectronics and thermoelectrics. Multiple empirical potentials have been developed for classical molecular dynamics (MD) simulations of this material, but it has been unclear which provides the most realistic results. Here, we calculate lattice thermal conductivity of single- and multilayer pristine ${\mathrm{MoS}}_2$ by employing three different thermal transport MD methods: equilibrium, nonequilibrium, and homogeneous nonequilibrium ones. We mainly use the Graphics Processing Units Molecular Dynamics code for numerical calculations, and the Large-scale Atomic/Molecular Massively Parallel Simulator code for crosschecks. Using different methods and computer codes allows us to verify the consistency of our results and facilitate comparisons with previous studies, where different schemes have been adopted. Our results using variants of the Stillinger-Weber potential are at odds with some previous ones and we analyze the possible origins of the discrepancies in detail. We show that, among the potentials considered here, the reactive empirical bond order (REBO) potential gives the most reasonable predictions of thermal transport properties as compared to experimental data. With the REBO potential, we further find that isotope scattering has only a small effect on thermal conduction in ${\mathrm{MoS}}_2$ and the in-plane thermal conductivity decreases with increasing layer number and saturates beyond about three layers. We identify the REBO potential as a transferable empirical potential for MD simulations of ${\mathrm{MoS}}_2$ which can be used to study thermal transport properties in more complicated situations such as in systems containing defects or engineered nanoscale features. This work establishes a firm foundation for understanding heat transport properties of ${\mathrm{MoS}}_2$ using MD simulations.

By revealing an underlying relation between the Dzyaloshinskii-Moriya interaction (DMI) and the scalar spin chirality, we have developed the theory of magnon thermal Hall effects in antiferromagnetic systems. The dynamic fluctuation of the scalar chirality is shown to directly respond to the nontrivial topology of magnon bands. In materials such as the jarosites compounds ${\mathrm{KFe}}_3{\left(\mathrm{OH}\right)}_6{\left({\mathrm{SO}}_4\right)}_2$ and veseignite ${\mathrm{BaCu}}_3{\mathrm{V}}_2{\mathrm{O}}_8{\left(\mathrm{OH}\right)}_2$ in the presence of in-plane DMI, the time-reversal symmetry can be broken by the fluctuations of scalar chirality even in the case of coplanar $\mathrm{q}=0$ magnetic configuration. The spin-wave Hamiltonian is influenced by a fictitious magnetic flux determined by the in-plane DMI. Topological magnon bands and corresponding nonzero Chern numbers are presented without the need of a canted noncoplanar magnetic ordering. The canting angle dependence of thermal Hall conductivity is discussed in detail as well. These results provide a clear principle of chirality-driven topological effects in antiferromagnetically coupled systems.

In this paper, we investigate exchange-biased square nanodots whose lateral sizes range between 130 and 500 nm, in comparison with continuous films by kinetic Monte Carlo simulations. We use a granular model which takes into account disordered interfacial phases by considering less stable magnetic grains at the interface in the antiferromagnetic (AF) layer. We further model the effect of the nanofabrication process by considering grains with reduced surfaces at the edges, due to grain cutting. Since less stable grains at the nanodot edges in the AF layer have been experimentally evidenced, we assumed a weaker anisotropy for the grains which are in the AF layer at the dot edges. Our results evidence two different mechanisms of the ferromagnetic (F) layer reversal depending on the magnitude of the coupling between F grains. In the weak coupling regime relative to the anisotropy, the exchange field is independent of the coupling and no variability from one nanodot to another is observed. By contrast, in the strong coupling regime, the exchange field depends on the coupling and it shows a high variability from one nanodot to another. Our model also well explain some experimental features observed in NiFe/IrMn nanodots (for various lateral sizes) and continuous films, at various measurement temperatures and various AF thicknesses. Finally, our model explains a long lasting issue about why the exchange field in nanodots can be either smaller or larger than in continuous films.

Doping dependence of the superconducting state structure and spin-fluctuation pairing mechanism in the $\mathrm{Ba}{\left(\mathrm{F}{\mathrm{e}}_{1-x}\mathrm{C}{\mathrm{o}}_x\right)}_2\mathrm{A}{\mathrm{s}}_2$ family is studied. BCS-like analysis of experimental data shows that in the overdoped regime, away from the antiferromagnetic (AFM) transition, the spin-fluctuation interaction between the electron and hole gaps is weak, and $\mathrm{Ba}{\left(\mathrm{F}{\mathrm{e}}_{1-x}\mathrm{C}{\mathrm{o}}_x\right)}_2\mathrm{A}{\mathrm{s}}_2$ is characterized by three essentially different gaps. In the three-gap state an anisotropic (nodeless) electron gap ${\mathrm{\Delta }}_e\left(x,\phi \right)$ has an intermediate value between the dominant inner ${\mathrm{\Delta }}_{2h}\left(x\right)$ and outer ${\mathrm{\Delta }}_{1h}\left(x\right)$ hole gaps. Close to the AFM transition the electron gap ${\mathrm{\Delta }}_e\left(x,\phi \right)$ increases sharply and becomes closer in magnitude to the dominant inner hole gap ${\mathrm{\Delta }}_{2h}\left(x\right)$. The same two-gap state with close electron and inner hole gaps ${\mathrm{\Delta }}_{2h}\left(x\right)\approx {\mathrm{\Delta }}_e\left(x,\phi \right)$ is also preserved in the phase of coexisting antiferromagnetism and superconductivity. The doping dependence of the electron gap ${\mathrm{\Delta }}_e\left(x,\phi \right)$ is associated with the strong doping dependence of the spin-fluctuation interaction in the AFM transition region. In contrast to the electron gap ${\mathrm{\Delta }}_e\left(x,\phi \right)$, the doping dependence of the hole gaps ${\mathrm{\Delta }}_{1,2h}\left(x\right)$ and the critical temperature $T_c\left(x\right)$, both before and after the AFM transition, are associated with a change of the density of states ${\gamma }_{nh}\left(x\right)$ and the intraband electron-phonon interaction in the hole bands. The nonphonon spin-fluctuation interaction in the hole bands in the entire Co concentration range is small compared with the intraband electron-phonon interaction and is not dominant in the $\mathrm{Ba}{\left(\mathrm{F}{\mathrm{e}}_{1-x}\mathrm{C}{\mathrm{o}}_x\right)}_2\mathrm{A}{\mathrm{s}}_2$ family.

We present here precise measurements of the resonance frequency, lifetime, and shape of confined acoustic modes in the tens of GHz regime in GaAs/AlAs superlattice planar and micropillar cavities at low temperatures ($\sim 20$ K). The subharmonic resonant pump-probe technique, where the repetition rate of the pump laser is tuned to a subharmonic of the cavity resonance to maximize the amplitude of the acoustic resonance, has been used in combination with a Sagnac interferometer technique for high sensitivity ($\sim 10$ fm) to the surface displacement. The cavity fundamental mode at $\sim 20$ GHz and the higher-order cavity harmonics up to $\sim 180$ GHz have been clearly resolved. Mechanical $Q$ values up to $2.7\times {10}^4$ have been measured in a planar superlattice, and the direct spatial mapping of confined acoustic modes in a superlattice micropillar cavity has been demonstrated. The $Q$-frequency product obtained is $\sim 5\times {10}^{14}$, demonstrating the suitability of these superlattice cavities for optomechanical applications.

The compression of ${\mathrm{SH}}_2$ and its subsequent decomposition to ${\mathrm{SH}}_3$, presumably in a cubic $Im\overline{3}m$ structure, has led to the discovery of conventional superconductivity with the highest measured and confirmed $T_c$ to date, 203 K at 160 GPa. Recent theoretical studies suggest that a mixture of S with other elements of the chalcogen group could improve the superconducting temperature. Here, we present a detailed analysis of the thermodynamic properties of S and Se mixtures in the bcc lattice with $Im\overline{3}m$ symmetry using a cluster expansion technique to explore the phase diagram of ${\mathrm{S}}_x{\mathrm{Se}}_{1-x}{\mathrm{H}}_3$. In contrast to earlier reports, we find that ${\mathrm{S}}_{0.5}{\mathrm{Se}}_{0.5}{\mathrm{H}}_3$ is not stable in the pressure range between 150 and 200 GPa. However, phases at compositions ${\mathrm{S}}_{0.2}{\mathrm{Se}}_{0.8}{\mathrm{H}}_3,{\mathrm{S}}_{0.\overline{3}}{\mathrm{Se}}_{0.\overline{6}}{\mathrm{H}}_3$, and ${\mathrm{S}}_{0.6}{\mathrm{Se}}_{0.4}{\mathrm{H}}_3$ are stable at 200 GPa, while additional phases at ${\mathrm{S}}_{0.25}{\mathrm{Se}}_{0.75}{\mathrm{H}}_3$ and ${\mathrm{S}}_{0.75}{\mathrm{Se}}_{0.25}{\mathrm{H}}_3$ are accessible at lower pressures. Electron-phonon calculations show that the values of $T_c$ are consistently lower for all ternary phases, indicating that mixtures of S and Se with H might not be a viable route towards compounds with improved superconducting properties.

The out-of-plane angular (${\theta }_{\mathrm{H}}$) dependence of the inverse spin Hall effect (ISHE) voltage ($V_{\mathrm{ISHE}}$) generated by spin pumping has been investigated in ${\mathrm{Y}}_3\mathrm{F}{\mathrm{e}}_5{\mathrm{O}}_{12}$ (YIG)/NiO/Pt trilayers. A simple sinusoidal angular dependence of $V_{\mathrm{ISHE}}$ has been viewed as a signature of spin pumping. Surprisingly, we observe an extensive plateau in the $V_{\mathrm{ISHE}}$ vs ${\theta }_{\mathrm{H}}$ plots with a pronounced peak feature at ${\theta }_{\mathrm{H}}\sim {45}^{\circ }$ to ${60}^{\circ }$ when the measurement temperature is close to the Néel temperature $\left(T_{\mathrm{N}}\right)$ of NiO. This phenomenon can be understood as arising from the competition between the exchange coupling at the YIG/NiO interface, the easy-plane and in-plane easy-axis anisotropies of NiO, and the effect of the applied magnetic field. While insulating antiferromagnetic films can efficiently transmit spin currents and show promise for integration in spintronic devices, the underlying physics of spin ordering and dynamics is richer than currently understood.