We report temperature and density dependences of the spin susceptibility of strongly interacting electrons in Si inversion layers. We measured (i) the itinerant electron susceptibility ${\chi }^{*}$ from the Shubnikov-de Haas oscillations in crossed magnetic fields and (ii) thermodynamic susceptibility ${\chi }_{\mathrm{T}}$ sensitive to all the electrons in the layer. Both ${\chi }^{*}$ and ${\chi }_{\mathrm{T}}$ are strongly enhanced with lowering the electron density in the metallic phase. However, there is no sign of divergency of either quantity at the density of the metal-insulator transition $n_c$. Moreover, the value of ${\chi }_{\mathrm{T}}$, which can be measured across the transition down to very low densities deep in the insulating phase, increases with density at $n<n_c$, as expected. In the absence of magnetic field, we found the temperature dependence of ${\chi }^{*}$ to be consistent with Fermi-liquid-based predictions, and to be much weaker than the power law predicted by non-Fermi-liquid models. We attribute a much stronger temperature dependence of ${\chi }_{\mathrm{T}}$ to localized spin droplets. In strong enough in-plane magnetic field, we found the temperature dependence of ${\chi }^{*}$ to be stronger than that expected for the Fermi liquid interaction corrections.

A time- and polarization-resolved pump-probe reflective interferometry measurement of fused silica excited by a femtosecond laser pulse above the damage threshold is presented. We compare the evolution of both the amplitude and the phase of the reflectivity with a rate equation coupled with a Drude model, widely used to interpret pump-probe experiments where a laser probe interacts with an excited semiconductor or dielectric. Despite the success reported in literature of such a model to reproduce experiments on a wide band-gap dielectric below the damage threshold, we show that it is not valid in the regime of interaction explored in this paper. The dielectric function at the laser wavelength is directly retrieved from our measurements, and several hypotheses are proposed to account for the observations.

We reveal the orbital-selective metal-insulator transition in a $4d$ multiorbital system, ${\mathrm{Sr}}_3{\left({\mathrm{Ru}}_{1-x}{\mathrm{Mn}}_x\right)}_2{\mathrm{O}}_7\left(x=0-0.2\right)$, by means of angle-resolved photoemission spectroscopy. With a small substitution $\left(x=0.05\right)$ of Mn with localized $3d$ orbitals, the spectra for the $4d_{xy}$ band become incoherent with a large gap, while the $4d_{xz/yz}$ bands stay metallic with sharp quasiparticle peaks. Intriguingly, this lifts band hybridization among $4d$ orbitals, and causes a two- to one-dimensional crossover in the remaining Fermi surface. Significant nesting in the remaining Fermi surface is implied to induce the reported magnetic ordering, and yields the insulating bulk state at higher Mn substitution, where all bands are gapped and totally incoherent. The availability of orbital-selective tuning of the pseudogap by a small impurity will prompt further theoretical studies of Hund's metals, which were recognized only recently in condensed matter physics.

We present a study of the transmission of electrons through a semiconductor quantum wire with strong spin-orbit coupling in proximity to an $s$-wave superconductor, which is Coulomb blockaded. Such a system supports Majorana zero modes in the presence of an external magnetic field. Without superconductivity, phase lapses are expected to occur in the transmission phase, and we find that they disappear when a topological superconducting phase is stabilized. We express tunneling through the nanowire with the help of effective matrix elements, which depend on both the fermion parity of the wire and the overlap with Bogoliubov–de Gennes wave functions. Using a modified scattering matrix formalism, that allows for including electron-electron interactions, we study the transmission phase in different regimes.

We study the neutral and charged optical excitations (excitons and trion) in the prototypical wide-gap insulator LiF using the first-principles $GW/\mathrm{BSE}$ approach and its extension for trions. In addition to neutral excitons we find bound trion states with a trion binding energy of 20–30 meV. At the same time the lowest bright exciton and trion are well separated by about 400 meV in the absorption spectrum both for the bulk and the (001) surface crystal. Even though the charged trions are slightly more extended compared to their neutral counterparts, they remain localized on a few atoms only and keep the Frenkel-like character of the neutral excitons. With such strongly localized trions, LiF stands out from currently investigated trionic materials and highlights itself for further studies.

We report on the magnetic, thermodynamic, and electronic properties of the Gd-doped Kondo-lattice compound ${\mathrm{YbFe}}_2{\mathrm{Zn}}_{20}$ ($T_K\approx 32$ K) by means of $T$-dependent magnetization, specific heat, and electron spin resonance (ESR) measurements. As Gd is incorporated in this system (${\mathrm{Yb}}_{1-x}{\mathrm{Gd}}_x{\mathrm{Fe}}_2{\mathrm{Zn}}_{20}$), the Yb contribution to the Sommerfeld coefficient remains almost unaltered for $x$ = 0.005 and 0.01 at ${\gamma }_{\mathrm{eff}}\approx$ 500 mJ ${\mathrm{mol}}^{-1}$ ${\mathrm{K}}^{-2}$, however, for $x=0.05$, it is reduced to ${\gamma }_{\mathrm{eff}}=450$ mJ ${\mathrm{mol}}^{-1}$ ${\mathrm{K}}^{-2}$. As expected for heavy-fermion systems, the ${\mathrm{Gd}}^{3+}$ ESR experiments show an enhanced Korringa relaxation rate, $b=d\left(\mathrm{\Delta }H\right)/\left(dT\right)$, due to the exchange interaction between the ${\mathrm{Gd}}^{3+}$ localized magnetic moment and the high $4f$-conduction electrons ($ce$) density of states at the Fermi level. Below $T_K$, the ${\mathrm{Gd}}^{3+}$ ESR $g$ shift presents a peculiar $T$ dependence. For $x\lesssim 0.01$, we associate the $g$ shift to an internal molecular AFM field due to the $ce$ screening of the ${\mathrm{Yb}}^{3+}$ magnetic moments in the Kondo condensate with a value of $\lambda =-2.80\left(1\right)$ mol Oe/emu. The negative value reflects a singlet nonmagnetic ground-state formation, consistent with a Kondo-lattice system. Still below $T_K$, but for $x=0.05$, the ${\mathrm{Gd}}^{3+}$ ESR $g$ shift presents a positive $T$ dependence, which we now associate to an internal molecular FM field due to a ${\mathrm{Gd}}^{3+}-{\mathrm{Gd}}^{3+}$ superexchangelike interaction via extended Fe $3d$ $ce$. A Fermi surface reconstruction process is found to take place in the crossover from the high-$T$ to low-$T$ regimes, such that a momentum transfer dependence of the ${\mathrm{Gd}}^{3+}-ce$ exchange interaction $\left[J_{f-ce}\left(q\right)\right]$ in the former is lost as the Kondo condensate sets in.

We propose a solid-state hybrid platform based on an array of implanted nitrogen-vacancy (NV) centers in diamond magnetically coupled to a mechanical oscillator. The mechanical oscillator and the NV electronic spins both act as a quantum bus and allow us to induce an effective long-range interaction between distant nuclear spins, relaxing the requirements on their spatial distance. The coherent nuclear spin-spin interaction, having the form of an Ising model, can be maintained in the presence of mechanical damping and spin dephasing via a pulsed dynamical decoupling of the nuclear spins in addition to the microwave driving field of the electronic spins. The present hybrid platform provides a scalable way to prepare multipartite entanglement among nuclear spins with long coherence times and can be applied to generate graph states that may be used for universal quantum computing.

Kepler's observation of comet tails initiated the research on the radiation pressure of celestial objects and 250 years later they found new incarnation after the Maxwell's equations were formulated to describe a plethora of light-matter coupling phenomena. Further, quantum mechanics gave birth to the photon drag effect. Here, we develop a microscopic theory of this effect which can occur in a general system containing Bose-Einstein–condensed particles, which possess an internal structure of quantum states. By analyzing the response of the system to an external electromagnetic field we find that such a drag results in a flux of particles constituting both the condensate and the excited states. We show that in the presence of the condensed phase, the response of the system acquires steplike behavior as a function of the electromagnetic field frequency with the elementary step determined by the internal energy structure of the particles.

We address the interpretation proposed in the paper [Simon, Phys. Rev. B 97, 121406(R) (2018)] of the thermal conductance data from [Banerjee et al., Nature (London) 559, 205 (2018)]. We show that the interpretation is inconsistent with experimental data and the sample structure. In particular, the paper misses the momentum mismatch between contrapropagating modes. Contrary to the claim of the paper, low energy tunneling involves a large momentum change. We consider only the “small Majorana velocity” mechanism [Simon, Phys. Rev. B 97, 121406(R) (2018)]. Other mechanisms, interpretations of the experiment, and their difficulties are beyond the scope of this Comment.

Feldman argues that simply having a large velocity mismatch and long wavelength disorder is not likely to result in sufficient non-equilibration of Majorana edge modes at $\nu =5/2$ to explain recent thermal transport experiments. I agree that this picture alone is probably too simple, although small modifications of the mechanism could still be viable.

Magnetic anisotropy controls the orientational stability and switching properties of magnetic states, and therefore plays a central role in spintronics. First-principles density functional theory calculations are able, in most cases, to provide a satisfactory description of bulk and interface contributions to the magnetic anisotropy of particular film/substrate combinations. In this paper we focus on achieving a simplified understanding of some trends in interfacial magnetic anisotropy based on a simple tight-binding model for quasiparticle states in a heavy-metal/ferromagnetic-metal bilayer film. We explain how to calculate the magnetic anisotropy energy of this model from the quasiparticle spin susceptibility, compare with more conventional approaches using either a perturbative treatment of spin-orbit interactions or a direct calculation of the dependence of the energy on the orientation of the magnetization, and show that the magnetic anisotropy can be interpreted as a competition between a Fermi sea term favoring perpendicular anisotropy and a Fermi surface term favoring in-plane anisotropy. Based on this finding, we conclude that perpendicular magnetic anisotropy should be expected in an itinerant electron thin film when the spin magnetization density is larger than the product of the band exchange splitting and the Fermi level density of states of the magnetic state.

Ab initio low-energy effective Hamiltonians of two typical high-temperature copper-oxide superconductors, whose mother compounds are ${\mathrm{La}}_2{\mathrm{CuO}}_4$ and ${\mathrm{HgBa}}_2{\mathrm{CuO}}_4$, are derived by utilizing the multiscale ab initio scheme for correlated electrons (MACE). The effective Hamiltonians obtained in the present study serve as platforms of future studies to accurately solve the low-energy effective Hamiltonians beyond the density functional theory. It allows further study on the superconducting mechanism from first principles and a quantitative basis without adjustable parameters not only for the available cuprates but also for future design of higher $T_{\mathrm{c}}$ in general. More concretely, we derive effective Hamiltonians for three variations: (1) a one-band Hamiltonian for the antibonding orbital generated from strongly hybridized Cu $3d_{x^2-y^2}$ and O $2p_{\sigma }$ orbitals, (2) a two-band Hamiltonian constructed from the antibonding orbital and Cu $3d_{3z^2-r^2}$ orbital hybridized mainly with the apex oxygen $p_z$ orbital, and (3) a three-band Hamiltonian consisting mainly of Cu $3d_{x^2-y^2}$ orbitals and two O $2p_{\sigma }$ orbitals. Differences between the Hamiltonians for ${\mathrm{La}}_2{\mathrm{CuO}}_4$ and ${\mathrm{HgBa}}_2{\mathrm{CuO}}_4$, which have relatively low and high critical temperatures $T_{\mathrm{c}}$, respectively, at optimally doped compounds, are elucidated. The main differences are summarized as follows: (i) the oxygen $2p_{\sigma }$ orbitals are farther ($\sim 3.7$ eV) below from the Cu $d_{x^2-y^2}$ orbital in the case of the La compound than the Hg compound ($\sim 2.4$ eV) in the three-band Hamiltonian. This causes a substantial difference in the character of the $d_{x^2-y^2}-2p_{\sigma }$ antibonding band at the Fermi level and makes the effective onsite Coulomb interaction $U$ larger for the La compound than the Hg compound for the two- and one-band Hamiltonians. (ii) The ratio of the second-neighbor to the nearest transfer $t^{\prime }/t$ is also substantially different (0.26 for the Hg and 0.15 for the La compound) in the one-band Hamiltonian. Heavier entanglement of the two bands in the two-band Hamiltonian implies that the two-band rather than the one-band Hamiltonian is more appropriate for the La compound. The relevance of the three-band description is also discussed especially for the Hg compound.

Electronic stopping power in warm dense matter can affect energy transport and heating in astrophysical processes and internal confinement fusion. For cold condensed matter systems, stopping power can be modeled from first-principles using real-time time-dependent density functional theory (DFT). However, high temperatures (10's to 100's of eV) may be computationally prohibitive for traditional Mermin-Kohn-Sham DFT. New experimental measurements in the warm dense regime motivates the development of first-principles approaches, which can reach these temperatures. We have developed a time-dependent orbital-free density functional theory, which includes a novel nonadiabatic and temperature-dependent kinetic energy density functional, for the simulation of stopping power at any temperature. The approach is nonlinear with respect to the projectile perturbation, includes all ions and electrons, and does not require a priori determination of screened interaction potentials. Our results compare favorably with Kohn-Sham for temperatures in the WDM regime, especially nearing 100 eV.

We demonstrate the strong tunability of the spin-pumping contribution to magnetic damping in a thin-film ferromagnetic free layer interfacing with a synthetic ferrimagnet (SFM), acting as a spin sink, via a thin Cu spacer. The effect strongly depends on the magnetic state of the SFM, a trilayer structure composed of two Fe layers coupled via indirect exchange mediated by a Cr spacer. With increasing Cr thickness, the SFM state undergoes a transition from an antiparallel configuration via a noncollinear configuration to a parallel configuration. We can explain the corresponding nonmonotonous dependence of spin relaxation in the free layer in terms of modulation of the longitudinal spin transport as well as relaxation of the transverse angular momentum in the SFM. The results should be useful for designing high-speed spintronic devices where tunability of spin relaxation is advantageous.

The interplay between competing short-range (SR) and long-range (LR) interactions can cause nontrivial structures in phase diagrams. Recently, horn-shaped unusual structures were found by Monte Carlo simulations in the phase diagram of the Ising antiferromagnet (IA) with infinite-range ferromagnetic-like (F) interactions [Phys. Rev. B 93, 064109 (2016); Phys.Rev.B 96, 174428 (2017)], and also in an IA with LR interactions of elastic origin modeling spin-crossover materials [Phys. Rev. B 96, 144425 (2017)]. To clarify the nature of the phases associated with the horn structures, we study the phase diagram of the IA model with infinite-range F interactions by applying a variational free energy in a cluster mean-field (CMF) approximation. While the simple Bragg-Williams mean-field theory for each sublattice does not produce a horn structure, we find such structures with the CMF method. This confirms that the local thermal fluctuations enabled by the multisite clusters are essential for this phenomenon. We investigate in detail the structure of metastable phases in the phase diagram. In contrast to the phase diagram obtained by the Monte Carlo studies, we find a triple point, at which ferromagnetic-like, antiferromagnetic-like, and disordered phases coexist, and also six tristable regions accompanying the horn structure. We also point out that several characteristic endpoints of first-order transitions appear in the phase diagram. We propose three possible scenarios for the transitions related to the tristable regions. Finally, we discuss the relation between the triple point in this phase diagram and that of a possible lattice-gas model, in which solid, liquid, and gas phases can coexist.

An analysis is presented of the ${}^{237}\mathrm{Np}-{}^{17}\mathrm{O}$ cross-relaxation (CR) process at temperatures below $T=10$ K that was reported [Tokunaga et al., Phys. Rev. B 74, 064421 (2006)] in ${}^{17}\mathrm{O}$ NMR studies of ${\mathrm{NpO}}_2$. The CR evidently results from ${}^{237}\mathrm{Np}$ spin fluctuations driven by indirect spin-spin interactions analogous to the Suhl-Nakamura [Nakamura, Prog. Theor. Phys. 20, 542 (1958)] effect in conventional magnets. Here, however, there is a body of evidence that the interacting ${\mathrm{Np}}^{4+}$ ions are in a magnetic, rank-5 dotriakontadipolar ground state [Santini et al., Phys. Rev. Lett. 97, 207203 (2006); Magnani et al., Phys. Rev. B 78, 104425 (2008)]. Owing to the observed exponential form of the fluctuation spectrum, it is possible to evaluate explicitly the CR bandwidth in terms of any specified ${}^{237}\mathrm{Np}-{}^{237}\mathrm{Np}$ (spin-spin) coupling Hamiltonian. We model the latter as an enhanced dipolar coupling. The enhancement is concluded to be compound, with the “enlarged nuclear moment” mechanism identified in the paramagnetic state [Tokunaga et al., Phys. Rev. B 74, 064421 (2006)] responsible for a factor $\sim 22$, while the indirect ${}^{237}\mathrm{Np}-{}^{237}\mathrm{Np}$ coupling effect is found to be $\sim 240$ times the amplitude of the classical dipolar interaction. We suggest that these results are consistent with the identification of a magnetic rank 5 multipolar ground state [Magnani et al., Phys. Rev. B 78, 104425 (2008)] for ${\mathrm{NpO}}_2$.

We report the Raman scattering measurements on the triple-layer ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{Ca}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{10+\mathrm{z}}$ (Bi2223) crystals of four different doping levels from slightly overdoped to strongly underdoped regimes. We observed a double pair breaking peak in the antinodal $B_{1\mathrm{g}}$ configuration that we attribute to the two antinodal gaps opening on the outer and inner $\mathrm{Cu}{\mathrm{O}}_2$ plane (OP and IP) band, respectively. The doping dependence of the pair breaking peak energy was investigated. Considering the difference in doping level between the IP and OP, all the $B_{1\mathrm{g}}$ pair breaking peak energies for OP and IP were found to align on a single line as a function of doping, which is consistent with the previous results on the double and monolayer cuprates. Within our experimental accuracy the IP and OP peaks start to appear almost at the same temperature. These findings suggest some sort of interaction between the layers. The observed gap energy is very large, not scaling with $T_{\mathrm{c}}$.

We analyze a family of two-dimensional BCS Hamiltonians with general $l$-wave pairing interactions, classifying the models in this family that are Bethe-ansatz solvable in the finite-size regime. We show that these solutions are characterized by nontrivial winding numbers, associated with topological phases, in some part of the corresponding phase diagrams. By means of a comparative study, we demonstrate benefits and limitations of the mean-field approximation, which is the standard approach in the limit of a large number of particles. The mean-field analysis also allows us to extend part of the results beyond integrability, clarifying the peculiarities associable with the integrability itself.

We investigate the edge magnetism and the spin transport properties of an SU(2)-symmetric Kitaev spin liquid (KSL) model put forward by Yao and Lee [Phys. Rev. Lett. 107, 087205 (2011)] on the honeycomb lattice. In this model, the spin degrees of freedom fractionalize into a ${\mathbb{Z}}_2$ static gauge field and three species of either gapless (Dirac) or gapped (chiral) Majorana fermionic excitations. We find that, when a magnetic field is applied on a zigzag edge, the Dirac KSL exhibits a nonlocal magnetization associated with the existence of zero-energy edge modes. The application of a spin bias $V={\mu }_{\uparrow }-{\mu }_{\downarrow }$ at the interface of the spin system with a normal metal produces a spin current into the KSL, which depends as a power law on $V$, in the zero-temperature limit, for both Dirac and chiral KSLs, but with different exponents. Lastly, we study the longitudinal spin Seebeck effect, in which a spin current is driven by the combined action of a magnetic field perpendicular to the plane of the honeycomb lattice and a thermal gradient at the interface of the KSL with a metal. Our results suggest that edge magnetization and spin transport can be used to probe the existence of charge-neutral edge states in quantum spin liquids.