Current induced forces are not only related with the discrete nature of electrons but also with its quantum character. It is natural then to wonder about the effect of decoherence. Here, we develop the theory of current induced forces including dephasing processes and we apply it to study adiabatic quantum motors (AQMs). The theory is based on Büttiker's fictitious probe model, which here is reformulated for this particular case. We prove that it accomplishes the fluctuation-dissipation theorem. We also show that, in spite of decoherence, the total work performed by the current induced forces remains equal to the pumped charge per cycle times the voltage. We find that decoherence affects not only the current induced forces of the system but also its intrinsic friction and noise, modifying in a nontrivial way the efficiency of AQMs. We apply the theory to study an AQM inspired by a classical peristaltic pump where we surprisingly find that decoherence can play a crucial role by triggering its operation. Our results can help to understand how environmentally induced dephasing affects the quantum behavior of nanomechanical devices.

Recent theoretical insights into the possibility of non-Abelian phases in $\nu =2/3$ fractional quantum Hall states revived the interest in the numerical phase diagram of the problem. We investigate the effect of various kinds of two-body interlayer couplings on the (330) bilayer state and exactly solve the Hamiltonian for up to 14 electrons on sphere and torus geometries. We consider interlayer tunneling, short-ranged repulsive/attractive pseudopotential interactions, and Coulomb repulsion. We find a 6-fold ground-state degeneracy on the torus when the interlayer hollow-core interaction is dominant. To identify the topological nature of this phase we measure the orbital-cut entanglement spectrum, quasihole counting, topological entanglement entropy, and wave-function overlap. Comparing the numerical results to the theoretical predictions, we interpret this 6-fold ground-state degeneracy phase to be the non-Abelian bilayer Fibonacci state.

We report detailed Knight-shift measurements of the two indium sites in the heavy-fermion compound ${\mathrm{CeIrIn}}_5$ as a function of temperature and field orientation. We find that the Knight-shift anomaly is orientation dependent, with a crossover temperature $T^{*}$ that varies by 50% as the field is rotated from (001) to (100). This result suggests that the hybridization between the Ce $4f$ states and the itinerant conduction electrons is anisotropic, a result that reflects its collective origin, and may lead to anisotropic Kondo liquid behavior and unconventional superconductivity.

We investigate the Josephson effect in a bilayer graphene flake contacted by two monolayer sheets deposited by superconducting electrodes. It is found that when the electrodes are attached to the different layers of the bilayer, the Josephson current is in a $\pi$ state, if the bilayer region is undoped and there is no vertical bias. Applying doping or bias to the junction reveals $\pi -0$ transitions which can be controlled by varying the temperature and the junction length. The supercurrent reversal here is very different from the ferromagnetic Josephson junctions where the spin degree of freedom plays the key role. We argue that the scattering processes accompanied by layer and sublattice index change give rise to the scattering phases, the effect of which varies with doping and bias. Such scattering phases are responsible for the $\pi -0$ transitions. On the other hand, if both of the electrodes are coupled to the same layer of the flake or the flake has AA stacking instead of common AB, the junction will be always in 0 state since the layer or sublattice index is not changed.

We performed inelastic neutron scattering measurements on single crystals of ${\mathrm{NdFe}}_3\left({}^{11}\mathrm{BO}_3\right){}_4$ to explore the magnetic excitations, to establish the underlying Hamiltonian, and to reveal the detailed nature of hybridization between the $4f$ and $3d$ magnetism. The observed spectra exhibiting a couple of key features, i.e., anticrossing of Nd and Fe excitations and anisotropy gap at the antiferromagnetic zone center, are explained by the magnetic model including spin interaction in the framework of weakly coupled ${\mathrm{Fe}}^{3+}$ chains, interaction between the ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Nd}}^{3+}$ moments, and single-ion anisotropy derived from the ${\mathrm{Nd}}^{3+}$ crystal field. The combination of the measurements and calculations reveals that the hybridization between $4f$ and $3d$ magnetism propagates the local magnetic anisotropy of the ${\mathrm{Nd}}^{3+}$ moment to the ${\mathrm{Fe}}^{3+}$ network, leading to the determination of the bulk structure of both electric polarization and magnetic moment in the multiferroics of the spin-dependent metal-ligand hybridization type.

The relative magnitude of electrical and thermal spin currents is investigated for a ferromagnetic tunnel contact on a semiconductor. A direct quantitative comparison is made by simultaneously generating electrical and thermal spin currents of opposite sign and determining the compensation point at which the sum of both spin currents vanishes. This avoids the need to determine the magnitude of each spin current. Surprisingly, it is found that in a $\mathrm{C}{\mathrm{o}}_{70}\mathrm{F}{\mathrm{e}}_{30}/\mathrm{MgO}/\mathrm{Si}$ tunnel contact, the thermal spin current driven by a temperature difference of less than 1 K across the contact is comparable to the electrical spin current induced by a bias voltage of about 22 mV. This suggests that the thermal generation of spin current is more efficient than hitherto assumed and should be considered in the design and analysis of spintronic devices that use spin current or spin transfer torque.

We report that the spin current generated by the spin Seebeck effect (SSE) in yttrium iron garnet (YIG) can be detected by a ferromagnetic metal (NiFe). By using the ferromagnetic/antiferromagnetic (FM/AFM) exchange bias structure (NiFe/IrMn), the inverse spin Hall effect (ISHE) and planar Nernst effect (PNE) of NiFe can be unambiguously separated, allowing us to observe a pure ISHE signal. After eliminating the in-plane temperature gradient in NiFe, we can even observe a pure ISHE signal without PNE from NiFe itself. It is worth noting that a large spin Hall angle (0.098) of NiFe is obtained, which is comparable with Pt. This work provides a kind of FM/AFM exchange bias structure to detect the spin current by charge signals, and highlights that ISHE in ferromagnetic metals can be used in spintronic research and applications.

It is shown that a linear polarized laser can cause magnetization of a spin system with magnetic anisotropy, the distinguished axis of which is perpendicular to the polarization of the laser field. In the dynamical regime the magnetization oscillates around the nonzero value determined by the parameters of the system. Oscillations have the frequency of the laser field, modulated by the lower Rabi-like frequencies. In the steady-state regime, for a large time scale greater than the characteristic relaxation time, the Rabi-like oscillations are damped, and the magnetization oscillates with the frequency of the laser field around the value which is determined by the relaxation rate also. Analytic results are presented for the spin-1/2 chain. The most direct manifestation of such a behavior can be observed in spin-1/2 Ising chain materials if the linear polarization of the laser field is chosen to be perpendicular to the Ising axis.

In elastically coupled multiferroic heterostructures that exhibit full domain correlations between ferroelectric and ferromagnetic subsystems, magnetic domain walls are firmly pinned on top of ferroelectric domain boundaries. In this work, we investigate the influence of pinned magnetic domain walls on the magnetization reversal process in a ${\mathrm{Co}}_{40}{\mathrm{Fe}}_{40}{\mathrm{B}}_{20}$ wedge film that is coupled to a ferroelectric ${\mathrm{BaTiO}}_3$ substrate via interface strain transfer. We show that the magnetic field direction can be used to select between two distinct magnetization reversal mechanisms, namely, (1) double switching events involving alternate stripe domains at a time or (2) synchronized switching of all domains. Furthermore, scaling of the switching fields with domain width and film thickness is also found to depend on the field orientation. These results are explained by considering the dissimilar energies of the two types of pinned magnetic domain walls that are formed in the system.

We study the anomalous Hall-like effect (AHLE) and the effective anisotropic magnetoresistance (EAMR) in antiferromagnetic $\gamma -{\mathrm{IrMn}}_3/{\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}\left(\mathrm{YIG}\right)$ and Pt/YIG heterostructures. For $\gamma -{\mathrm{IrMn}}_3/\mathrm{YIG}$, the EAMR and the AHLE resistivity change sign with temperature due to the competition between the spin Hall magnetoresistance (SMR) and the magnetic proximity effect (MPE) induced by the interfacial antiferromagnetic uncompensated magnetic moment. In contrast, for Pt/YIG, the AHLE resistivity changes sign with temperature whereas no sign change is observed in the EAMR. This is because the MPE and the SMR play a dominant role in the AHLE and the EAMR, respectively. As different types of galvanomagnetic properties, the AHLE and the EAMR have proved vital in disentangling the MPE and the SMR in metal/insulating-ferromagnet heterostructures.

The fluctuation theorem establishes general relations between transport coefficients and fluctuations in nonequilibrium systems. Recently there has been much interest in quantum fluctuation relations for electric currents. Since charge carriers also carry spin, it is important to extend the fluctuation theorem to spin currents. We use the principle of microscopic reversibility to derive such theorem. As a consequence, we obtain a family of relations between transport coefficients and fluctuations of spin currents. We apply the relations to the spin Seebeck effect and rectification of spin currents. Our relations do not depend on a microscopic model and hence can be used to test the validity of theoretical approximations in spin-transport problems.

Static field properties of magnetoelectric hexaferrites have been explored extensively in the past five years. In this paper, dynamic properties of magnetoelectric hexaferrites are being explored. In particular, effects of the linear magnetoelectric coupling $\left(\alpha \right)$ on ferrimagnetic resonance (FMR) and magnetoelastic excitations are being investigated. A magnetoelastic free energy which includes Landau-Lifshitz mathematical description of a spin spiral configuration is proposed to calculate FMR and magnetoelastic excitations in magnetoelectric hexaferrites. It is predicted that the ordinary uniform precession FMR mode contains resonance frequency shifts that are proportional to magnetoelectric static and dynamic fields. The calculated FMR fields are in agreement with experiments. Furthermore, it is predicted at low frequencies (approximately megahertz ranges), near zero magnetic field FMR frequencies, there is an extra uniform precession FMR mode besides the ordinary FMR mode which can only be accounted by dynamic magnetoelectric fields. Whereas the FMR frequency shifts in the ordinary FMR mode due to the $\alpha$ coupling scale as $\alpha$, the shifts in the new discovered FMR mode scale as ${\alpha }^2$. Also, magnetoelastic dispersions were calculated, and it is predicted that the effect of the $\alpha$ coupling are the following: (1) The strength of admixture of modes and splitting in energy between spin waves and transverse acoustic waves is proportional to $\alpha$. (2) The degeneracy of the two transverse acoustic wave modes is lifted even for relatively low values of $\alpha$. Interestingly, at low frequencies near zero field FMR frequencies, the surface spin wave mode branch flip-flops with the volume spin wave branch whereby one branch assumes real values of the propagation constant and the other purely imaginary upon the application of a static electric field.

We investigate the importance of superconducting order parameter fluctuations in the 122 family of Fe-based superconductors, using high-resolution specific heat and thermal expansion data of various $\mathrm{B}{\mathrm{a}}_{1-x}{\mathrm{K}}_x\mathrm{F}{\mathrm{e}}_2\mathrm{A}{\mathrm{s}}_2$ single crystals covering a large range of the phase diagram from the strongly underdoped to the overdoped regime. By applying scaling relations of the $3d-\mathrm{XY}$ and the $3d-\text{lowest-Landau-level}(3d-\mathrm{LLL})$ fluctuation models to data measured in different magnetic fields, we demonstrate that a strong increase of the critical fluctuation regime is responsible for the transition broadening in magnetic fields, which is a direct consequence of a magnetic-field-induced finite-size effect due to a reduction of the effective dimensionality by a decreasing magnetic length scale related to the mean vortex separation and the confinement of quasiparticles in LLL. The fluctuations are stronger in the underdoped and overdoped regimes and appear to be weakest at optimal doping.

Electromodulated reflectance (ER) is a standard characterization method to determine critical points such as the band gap in the band structure of semiconductors. These critical points show up as spectrally narrow features in ER and are typically evaluated using Aspnes's third-derivative functional form. ER spectra of stratified semiconductor systems such as thin-film solar cells, however, are significantly distorted by optical interference due to their layered structure. Furthermore, strong built-in electric fields result in a deviation from the typically assumed low-field conditions. We present here simulations of ER spectra from stratified systems based on transfer matrices using the Franz-Keldysh theory in its general form. For realistic thin-film solar cell conditions, distortions of ER line shapes due to the above-mentioned interferences and strong electric fields appear in the simulations. Furthermore, the results show good agreement with measured ER spectra of a structurally well-characterized $\mathrm{Cu}(\mathrm{In},\mathrm{Ga}){\mathrm{Se}}_2$ (CIGS) solar cell. Our analysis points out the restrictions on the determination of energetic position and number of critical points from ER spectra of stratified systems.

We investigate theoretically the long-distance coupling and spin exchange in an array of quantum dot spin qubits in the presence of microwaves. We find that photon-assisted cotunneling is boosted at resonances between photon and energies of virtually occupied excited states and show how to make it spin selective. We identify configurations that enable fast switching and spin echo sequences for efficient and nonlocal manipulation of spin qubits. We devise configurations in which the near-resonantly boosted cotunneling provides nonlocal coupling which, up to certain limit, does not diminish with distance between the manipulated dots before it decays weakly with inverse distance.

We present photoluminescence studies of CdTe and ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ quantum dots grown in two adjacent layers. We show that when the dots are 8 nm apart, their magneto-optical properties—Zeeman shifts and transition linewidths—are analogous to those of individual CdTe or ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ dots. When the dots are grown closer, at a distance of 4 nm, it becomes possible to tune the electron states to resonance and obtain a formation of a molecular state hybridized over the two dots. As a result of the resonant enhancement of the electron–Mn ion exchange interaction, spectroscopic signatures specific to spin-dependent interdot coupling appear. Namely, an anomalous increase of the Zeeman shift and a resonant increase in the transition linewidth are observed. A simple model calculation allows us to quantitatively reproduce the experimental results.

We demonstrate the ab initio electrical transport calculation limited by electron-phonon coupling by using the full solution of the Boltzmann transport equation (BTE), which applies equally to metals and semiconductors. Numerical issues are emphasized in this work. We show that the simple linear interpolation of the electron-phonon coupling matrix elements from a relatively coarse grid to an extremely fine grid can ease the calculational burden, which makes the calculation feasible in practice. For the Brillouin zone (BZ) integration of the transition probabilities involving one $\delta$ function, the Gaussian smearing method with a physical choice of locally adaptive broadening parameters is employed. We validate the calculation in the cases of $n$-type Si and Al. The calculated conductivity and mobility are in good agreement with experiments. In the metal case we also demonstrate that the Gaussian smearing method with locally adaptive broadening parameters works excellently for the BZ integration with double $\delta$ functions involved in the Eliashberg spectral function and its transport variant. The simpler implementation is the advantage of the Gaussian smearing method over the tetrahedron method. The accuracy of the relaxation time approximation and the approximation made by Allen [Phys. Rev. B 17, 3725 (1978)] has been examined by comparing with the exact solution of BTE. We also apply our method to $n$-type monolayer ${\mathrm{MoS}}_2$, for which a mobility of $150 {\mathrm{cm}}^2 {\mathrm{v}}^{-1} {\mathrm{s}}^{-1}$ is obtained at room temperature. Moreover, the mean free paths are less than 9 nm, indicating that in the presence of grain boundaries the mobilities should not be effectively affected if the grain boundary size is tens of nanometers or larger. The ab initio approach demonstrated in this paper can be directly applied to other materials without the need for any a priori knowledge about the electron-phonon scattering processes, and can be straightforwardly extended to study cases with electron-impurity scattering.

We present a detailed low-temperature scanning tunneling microscopy (STM) study of the commensurate charge density wave (CDW) in $1T-{\mathrm{TiSe}}_2$ in the presence of single atom defects. We find no significant modification of the CDW lattice in single crystals with native defect concentrations where some bulk probes already measure substantial reductions in the CDW phase transition signature. A systematic analysis of STM micrographs combined with density functional theory modeling of atomic defect patterns indicate that the observed CDW modulation lies in the Se surface layer. The defect patterns clearly show there are no $2H$-polytype inclusions in the CDW phase, as previously found at room temperature [A. N. Titov et al., Phys. Solid State 53, 1073 (2011)]. They further provide an alternative explanation for the chiral Friedel oscillations recently reported in this compound [J. Ishioka et al., Phys. Rev. B 84, 245125 (2011)].

We consider the thermodynamic consistency of the charge response function in the (extended) Hubbard model. In dynamical mean-field theory (DMFT), thermodynamic consistency is preserved. We prove that the static, homogeneous DMFT susceptibility is consistent as long as vertex corrections obtained from the two-particle impurity correlation function are included. In the presence of a nonlocal interaction, the problem may be treated within extended DMFT (EDMFT), or its diagrammatic extension, the dual boson approach. We show that here maintaining thermodynamic consistency requires knowledge of three- and four-particle impurity correlation functions, which are typically neglected. Nevertheless, the dual boson approximation to the response is remarkably close to consistency. This holds even when two-particle vertex corrections are neglected. EDMFT is consistent only in the strongly correlated regime and near half-filling, where the physics is predominantly local.

We reveal extraordinary electromagnetic properties for a general class of uniaxially polarizable media. Depending on parameters, such metamaterials may have a wide range of nontrivial shapes of isofrequency contours including lemniscate, diamond, and multiply connected curves with connectivity number reaching 5. The possibility of the dispersion engineering paves a way to more flexible manipulation of electromagnetic waves. Employing first-principles considerations we prove that uniaxially polarizable media should be described in terms of the nonlocal permittivity tensor which by no means can be reduced to local permittivity and permeability even in the long-wavelength limit. We introduce an alternative set of local material parameters including quadrupole susceptibility capable of capturing all of the second-order spatial dispersion effects.