It is predicted that a new class of systems, superconductor/normal metal (S/N) heterostructures, can reveal the in-plane Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) instability under nonequilibrium conditions at temperatures close to the critical temperature. It does not require any Zeeman interaction in the system. For S/N heterostructures under nonequilibrium distribution there is a natural easily adjustable parameter, the voltage, which can control the FFLO state. This FFLO state can be of different types: plane wave, stationary wave, and even two-dimensional structures are possible. Some types of FFLO state are accompanied by a magnetic flux, which can be observed experimentally. All the types of FFLO state can be revealed through the temperature dependence of the linear response of the system on the applied magnetic field near $T_c$, which strongly differs from that for the homogeneous state.

We present the results of muon-spin relaxation measurements on the triangular lattice Heisenberg antiferromagnet $\alpha$-KCrO${}_2$. We observe sharp changes in behavior at an ordering temperature of $T_{\mathrm{c}}=23$ K, with an additional broad feature in the muon-spin relaxation rate evident at $T=13$ K, both of which correspond to features in the magnetic contribution to the heat capacity. This behavior is distinct from both the Li- and Na-containing members of the series. These data may be qualitatively described with the established theoretical predictions for the underlying spin system.

We exploit the unique properties of optical waves in nanophotonic structures to enhance the capabilities for active control of electromagnetic thermal transfer at nanoscale. We show that the near-field thermal transfer between two nanospheres can exhibit a thermal rectification effect with very high contrast and large operating bandwidth. In this system, the scale invariance properties of the resonance modes result in a large difference in the coupling constants between relevant modes in the forward and reverse scenarios. Such a difference provides a mechanism for thermal rectification. The two-sphere system can also exhibit negative differential thermal conductance.

Droplet solitons are coherently precessing solitary waves that have been recently realized in thin ferromagnets with perpendicular anisotropy. In the strongly nonlinear regime, droplets can be well approximated by a slowly precessing, circular domain wall with a hyperbolic tangent form. Utilizing this representation, this work develops a general droplet modulation theory and applies it to study the long-range effects of the magnetostatic field and a nanocontact spin torque oscillator (NC-STO) where spin polarized currents act as a gain source to counteract magnetic damping. An analysis of the dynamical equations for the droplet's center, frequency, and phase demonstrates a negative precessional frequency shift due to long-range dipolar interactions, dependent on film thickness. Further analysis also demonstrates the onset of a saddle-node bifurcation at the minimum sustaining current for the NC-STO. The basin of attraction associated with the stable node demonstrates that spin torque enacts a restoring force to excursions of the droplet from the nanocontact center, observed previously in numerical simulations. Large excursions lead to the droplet's eventual decay into spin waves.

We investigate the transverse field Ising model on a diamond chain using series expansions about the high-field limit and exact diagonalizations. For the unfrustrated case we accurately determine the quantum critical point and its expected 2d Ising universality separating the polarized and the ${\mathcal{Z}}_2$ symmetry broken phase. In contrast, we find strong evidence for a disorder by disorder scenario for the fully-frustrated transverse field Ising model, i.e., except for the pure Ising model, having an extensive number of ground states, the system is always in a quantum disordered polarized phase. The low-energy excitations in this polarized phase are understood in terms of exact local modes of the model. Furthermore, an effective low-energy description for an infinitesimal transverse field allows us to pinpoint the quantum disordered nature of the ground state via mapping to an effective transverse field Ising chain and to determine the induced gap to the elementary effective domain wall excitation very accurately.

We develop a self-consistent theory for current-induced spin-wave excitations in normal metal/magnetic insulator bilayer structures. We compute the spin-wave dispersion and dissipation, including dipolar and exchange interactions in the magnet, the spin diffusion in the normal metal, as well as the surface anisotropy, spin-transfer torque, and spin pumping at the interface. We find that (1) the spin-transfer torque and spin pumping affect the surface modes more than the bulk modes; (2) spin pumping inhibits high-frequency spin-wave modes, thereby redshifting the excitation spectrum; (3) easy-axis surface anisotropy induces a new type of surface spin wave, which reduces the excitation threshold current and greatly enhances the excitation power. We propose that the magnetic insulator surface can be engineered to create spin-wave circuits utilizing surface spin waves as information carriers.

In ferromagnetic thin films, broken inversion symmetry and spin-orbit coupling give rise to interfacial Dzyaloshinskii-Moriya interactions. Analytic expressions for spin-wave properties show that the interfacial Dzyaloshinskii-Moriya interaction leads to nonreciprocal spin-wave propagation, i.e., different properties for spin waves propagating in opposite directions. In favorable situations, it can increase the spin-wave attenuation length. Comparing measured spin-wave properties in ferromagnet/normal metal bilayers and other artificial layered structures with these calculations could provide a useful characterization of the interfacial Dzyaloshinskii-Moriya interactions.

We have extended nonlocal orbital-free methods which enforce the correct linear response in the noninteracting uniform electron gas limit, developed at zero temperature for the kinetic energy to finite temperature for the full noninteracting free energy. Comparisons are made to the Thomas-Fermi approximation and to the orbital-dependent Kohn-Sham method. We find significantly improved agreement for the resulting functional with Kohn-Sham for a wide range of densities and temperatures. We also provide the necessary formulas for implementation in quantum molecular dynamics simulations.

We investigate the magnetic and metal-insulator (M-I) phase diagram of the $\frac{1}{5}$-depleted square-lattice Hubbard model at $\frac{1}{4}$ filling by the mean-field approximation. There exist three magnetic phases of nonmagnetic (N), antiferromagnetic (AF), and ferromagnetic (F) types, each realized for the large intrasquare hopping $t_1$, intersquare hopping $t_2$, and Coulomb interaction $U$, respectively. Within each magnetic phase, the M-I transition of Lifshitz type emerges and, finally, six kinds of phases are identified in the $U-t_1/t_2$ plane. When $t_1=t_2$, we find that the Dirac cone and nearly flat band around the $\Gamma$ point form the SU(3) multiplet. The SU(3) effective theory well describes the phase transitions between NI, paramagnetic-metal (PM), and AF phases. The NI and AFI phases are characterized by different Berry phases as in polyacetylene or graphene.

The stereoscopic angle-dependent magnetoresistance oscillations (AMRO) in an organic conductor $\alpha$-(BEDT-TTF)${}_2$KHg(SCN)${}_4$ were measured across the temperature-pressure boundary that separates the charge-density-wave state from the metallic state. The gnomonic projections of the data clearly resolved the contributions from different parts of the Fermi surfaces. The temperature and pressure dependencies of the AMRO results revealed the progressive formation of a quasi-one-dimensional orbit in the charge-density-wave state. The AMRO measurements at ambient pressures and at low temperatures revealed the presence of two sets of quasi-one-dimensional Fermi surfaces. Additional evidence for multiple quasi-one-dimensional orbits was obtained from the data collected in conjunction with the in-plane field rotations.

The interplay between interactions and disorder in closed quantum many-body systems is relevant for thermalization phenomenon. In this paper, we address this competition in an infinite temperature spin system by means of the Loschmidt echo (LE), which is based on a time reversal procedure. This quantity has been formerly employed to connect quantum and classical chaos, and in the present many-body scenario we use it as a dynamical witness. We assess the LE time scales as a function of disorder and interaction strengths. The strategy enables a qualitative phase diagram that shows the regions of ergodic and nonergodic behavior of the polarization under the echo dynamics.

The time-resolved change in the surface potential upon photoexcitation has been measured in two $n$-type photovoltaics, Si (111) 7×7 and ZnO ($10\overline{1}0$), using two different laser pump-synchrotron x-ray probe methodologies. Taken together, these experiments allow the dynamics of the surface photovoltage (SPV) to be monitored over timescales of subnanoseconds to milliseconds. The timescales for the photoinduced change in the SPV are dramatically different in the two samples, with measured SPV decay time constants of 6.6 μs for Si and up to 1.2 ms (dependent on surface oxygen concentration) for ZnO. The carrier dynamics at the Si (111) 7×7 surface are well modeled by a self-decelerating relaxation model involving the recombination of carriers by thermionic emission across the surface depletion layer on nanosecond timescales. In the case of ZnO ($10\overline{1}0$), a persistent photoconductivity (PPC) is observed, which is influenced by oxygen annealing conditions during sample preparation. Persistent photoconductivity is also observed when the surface is illuminated with subband-gap (405 nm) radiation, revealing that defect states approximately 340 meV above the valence band edge are directly associated with the PPC. We demonstrate that, under the conditions of our experiment, PPC mediated by these defects dominates over the oxygen photodesorption mechanism. These observations are consistent with the hypothesis that ionized oxygen vacancy states are responsible for PPC in ZnO.

Here we suggest a hybrid spin noise spectroscopy technique, which is sensitive to the spin Hall effect. Our main idea is to study correlations between transverse voltage fluctuations and spin polarization fluctuations, which appear as a result of spin-charge coupling that is fundamental for the spin Hall effect. It is shown that, while the standard spin-spin correlation function is not sensitive to the spin Hall effect, spin-transverse voltage and transverse voltage–transverse voltage correlation functions provide the missing sensitivity, which is linear and quadratic in the spin Hall coefficient, respectively. We anticipate that the proposed method could find applications in studies of spin-charge coupling in semiconductors and other materials.

Ionized nitrogen molecules (${}^{15}$N${}_2^{+}$) are used as efficient point sources for creating NV${}^{-}$ pairs in diamond with nanoscale spatial separation and up to 55 kHz magnetic coupling strength. Co-implantation of ${}^{12}$C${}^{+}$ increased the yield of pairs, and a ${}^{13}$C-depleted diamond allowed 0.65 ms coherence times to be obtained. Further coupling to a third dark spin provided a strongly coupled three-spin register. These results mark an important step towards realization of multiqubit systems and scalable NV${}^{-}$ quantum registers.

We demonstrate that spin polarization and valley polarization have quantitatively similar effects on the resistivity of a two-dimensional electron gas in a silicon-on-insulator quantum well. In so doing, we also examine the dependence on disorder, leading to a coarse but global phenomenology of how the resistivity depends on its key parameters: spin and valley polarization, density, disorder, and temperature.

We present a detailed analysis of the skew-scattering contribution to the spin Hall conductivity using an extended version of the resonant scattering model of Fert and Levy [Phys. Rev. Lett. 106, 157208 (2011)]. For $5d$ impurities in a Cu host, the proposed phase shift model reproduces the corresponding first-principles calculations. Crucial for that agreement is the consideration of two scattering channels related to $p$ and $d$ impurity states since the discussed mechanism is governed by a subtle interplay between the spin-orbit and potential scattering in both angular-momentum channels. It is shown that the potential scattering strength plays a decisive role for the magnitude of the spin Hall conductivity.

We investigate the electron spin degree of freedom in imbalanced density $\nu =1$ bilayer quantum Hall states using the resistively detected nuclear-spin–lattice relaxation rate $1/T_1$. The values of $1/T_1$ in imbalanced states increase rapidly in the vicinity of $\nu =1$, similar to the phenomenon that is observed in the region in which skyrmion crystals are formed. Furthermore, the value of $1/T_1$ in the back layer (the layer from which electrons are transferred to the front layer) also increases in the intermediate imbalanced state. These results indicate that the low-energy electron-spin mode, similar to the mode observed in skyrmion crystals, exists across the two layers. We suggest that such a mode arises in spin-pseudospin intertwined SU(4) skyrmions.

The persistent current in strictly one-dimensional Dirac systems is investigated within two different models, defined in the continuum and on a lattice, respectively. The object of the study is the effect of a single magnetic or nonmagnetic impurity in the two systems. In the continuum Dirac model, an analytical expression for the persistent current flowing along a ring with a single delta-like magnetic impurity is obtained after regularization of the unbounded negative energy states. The predicted decay of the persistent current agrees with the lattice simulations. The results are generalized to finite temperatures. To realize a single Dirac massless fermion, the lattice model breaks the time-reversal symmetry, and in contrast with the continuum model, a pointlike nonmagnetic impurity can lead to a decay in the persistent current.

Spin-orbit coupled superconductors are interesting candidates for realizing topological and potentially non-Abelian states with Majorana fermions. We argue that time-reversal broken spin-orbit coupled superconductors generically can be characterized as having subgap states that are bound to localized nonmagnetic impurities. Such bound states, which are referred to as the Shiba states, can be detected as sharp resonances in the tunneling spectrum of the spin-orbit coupled superconductors. The Shiba state resonance can be tuned using a gate voltage or a magnetic field from being at the edge of the gap at zero magnetic fields to crossing zero energy when the Zeeman splitting is tuned into the topological superconducting regime. The zero-crossing signifies a fermion parity changing first-order quantum phase transition, which is characterized by a Pfaffian topological invariant. These zero crossings of the impurity level can be used to locally characterize the topological superconducting state in topological nanowires from tunneling experiments.

The phonon dispersion of graphene on Ir(111) has been determined by means of angle-resolved inelastic electron scattering and density functional calculations. Kohn anomalies of the highest optical-phonon branches are observed at the $\overline{\Gamma }$ and $\overline{\text{K}}$ point of the surface Brillouin zone. At $\overline{\text{K}}$ the Kohn anomaly is weaker than observed for pristine graphene and graphite. This observation is rationalized in terms of a decrease of the electron-phonon coupling due to screening of graphene electron correlations by the metal substrate.