17 research outputs found
Quasilinear spin voltage profiles in spin thermoelectrics
Recent experiments show that spin thermoelectrics is a promising approach to
generate spin voltages. While spin chemical potentials are often limited to a
surface layer of the order of the spin diffusion length, we show that
thermoelectrically induced spin chemical potentials can extend much further in
itinerant ferromagnets with paramagnetic impurities. In some cases,
conservation laws, e.g., for a combination of spin and heat currents, give rise
to a linear spin voltage profile. More generally, we find quasilinear profiles
involving a spin thermoelectric length scale which far exceeds the spin
diffusion length.Comment: 4+ page
Anomalous Hall effect in a two dimensional electron gas with magnetic impurities
Magnetic impurities play an important role in many spintronics-related
materials. Motivated by this fact, we study the anomalous Hall effect in the
presence of magnetic impurities, focusing on two-dimensional electron systems
with Rashba spin-orbit coupling. We find a highly nonlinear dependence on the
impurity polarization, including possible sign changes. At small impurity
magnetizations, this is a consequence of the remarkable result that the linear
term is independent of the spin-orbit coupling strength. Near saturation of the
impurity spins, the anomalous Hall conductivity can be resonantly enhanced, due
to interference between potential and magnetic scattering.Comment: 5 pages, 3 figure
Microwave conductivity of d-wave superconductors with extended impurities
We investigate the influence of extended scatterers on the finite temperature
and finite frequency microwave conductivity of d-wave superconductors. For this
purpose we generalize a previous treatment by Durst and Lee, which is based on
a nodal approximation of the quasiparticle excitations and scattering
processes, and apply it to the analysis of experimental spectra of YBCO-123 and
BSCCO-2212. For YBCO, we find that accounting for a slight spatial extension of
the strong scattering in-plane defects improves the fit of the low temperature
microwave conductivity to experiment. With respect to BSCCO we conclude that it
is necessary to include a large concentration of weak-to-intermediate strength
extended scatterers, which we attribute to the out-of plane disorder introduced
by doping. These findings for BSCCO are consistent with similar analyses of the
normal state ARPES spectra and of STM spectra in the superconducting state,
where an enhanced forward scattering has been inferred as well.Comment: 10 pages, 11 figure
Dopant-modulated pair interaction in cuprate superconductors
Comparison of recent experimental STM data with single-impurity and
many-impurity Bogoliubov-de Gennes calculations strongly suggests that random
out-of-plane dopant atoms in cuprates modulate the pair interaction locally.
This type of disorder is crucial to understanding the nanoscale electronic
structure inhomogeneity observed in BSCCO-2212, and can reproduce observed
correlations between the positions of impurity atoms and various aspects of the
local density of states such as the gap magnitude and the height of the
coherence peaks. Our results imply that each dopant atom modulates the pair
interaction on a length scale of order one lattice constant.Comment: 5 pages, 4 figure
Andreev states near short-ranged pairing potential impurities
We study Andreev states near atomic scale modulations in the pairing
potential in both - and d-wave superconductors with short coherence lengths.
For a moderate reduction of the local gap, the states exist only close to the
gap edge. If one allows for local sign changes of the order parameter, however,
resonances can occur at energies close to the Fermi level. The local density of
states (LDOS) around such pairing potential defects strongly resembles the
patterns observed by tunneling measurements around Zn impurities in
BiSrCaCuO (BSCCO). We discuss how this phase impurity model
of the Zn LDOS pattern can be distinguished from other proposals
experimentally.Comment: 4 pages, 4 figure
Boltzmann approach to the longitudinal spin Seebeck effect
We develop a Boltzmann transport theory of coupled magnon-phonon transport in ferromagnetic insulators. The explicit treatment of the magnon-phonon coupling within the Boltzmann approach allows us to calculate the low-temperature magnetic-field dependence of the spin-Seebeck voltage. Within the Boltzmann theory we find that this magnetic field dependence shows similar features as found by Flebus et al. [Phys. Rev. B 95, 144420 (2017)] for a strongly coupled magnon phonon system that forms magnon-polarons, and consistent with experimental findings in yttrium iron garnet by Kikkawa et al. [Phys. Rev. Lett. 117, 207203 (2016)]. In addition to the anomalous magnetic-field dependence of the spin Seebeck effect, we also predict a dependence on the system size
Relaxation mechanisms of the persistent spin helix
We study the lifetime of the persistent spin helix in semiconductor quantum
wells with equal Rashba- and linear Dresselhaus spin-orbit interactions. In
order to address the temperature dependence of the relevant spin relaxation
mechanisms we derive and solve semiclassical spin diffusion equations taking
into account spin-dependent impurity scattering, cubic Dresselhaus spin-orbit
interactions and the effect of electron-electron interactions. For the
experimentally relevant regime we find that the lifetime of the persistent spin
helix is mainly determined by the interplay of cubic Dresselhaus spin-orbit
interaction and electron-electron interactions. We propose that even longer
lifetimes can be achieved by generating a spatially damped spin profile instead
of the persistent spin helix state.Comment: 12 pages, 2 figure
Current-induced switching in transport through anisotropic magnetic molecules
Anisotropic single-molecule magnets may be thought of as molecular switches,
with possible applications to molecular spintronics. In this paper, we
consider current-induced switching in single-molecule junctions containing an
anisotropic magnetic molecule. We assume that the carriers interact with the
magnetic molecule through the exchange interaction and focus on the regime of
high currents in which the molecular spin dynamics is slow compared to the
time which the electrons spend on the molecule. In this limit, the molecular
spin obeys a nonequilibrium Langevin equation which takes the form of a
generalized Landau-Lifshitz-Gilbert equation and which we derive
microscopically by means of a nonequilibrium Born-Oppenheimer approximation.
We exploit this Langevin equation to identify the relevant switching
mechanisms and to derive the current-induced switching rates. As a by-product,
we also derive S-matrix expressions for the various torques entering into the
Landau-Lifshitz-Gilbert equation which generalize previous expressions in the
literature to nonequilibrium situations.1\. Auflag
Thermodynamic transitions in inhomogeneous d-wave superconductors
We study the spectral and thermodynamic properties of inhomogeneous d-wave
superconductors within a model where the inhomogeneity originates from atomic
scale pair disorder. This assumption has been shown to be consistent with the
small charge and large gap modulations observed by scanning tunnelling
spectroscopy (STS) on BSCCO. Here we calculate the specific heat within the
same model, and show that it gives a semi-quantitative description of the
transition width in this material. This model therefore provides a consistent
picture of both surface sensitive spectroscopy and bulk thermodynamic
properties.Comment: 4 pages, 4 figure