Searcharxiv⌕ Search

arXiv subjects

Arne Brataas

Publications and source records attributed to Arne Brataas.

229 records · Page 13Linked to original sources
arXiv2000

Spin-accumulation and Andreev-reflection in a mesoscopic ferromagnetic wire

The electron transport though ferromagnetic metal-superconducting hybrid devices is considered in the non-equilibrium Green's function formalism in the quasiclassical approximation. Attention if focused on the limit in which the exchange splitting in the ferromagnet is much larger than the superconducting energy gap. Transport properties are then governed by an interplay between spin-accumulation close to the interface and Andreev reflection at the interface. We find that the resistance can either be enhanced or lowered in comparison to the normal case and can have a non-monotonic temperature and voltage dependence. In the non-linear voltage regime electron heating effects may govern the transport properties, leading to qualitative different behaviour than in the absence of heating effects. Recent experimental results on the effect of the superconductor on the conductance of the ferromagnet can be understood by our results for the energy-dependent interface resistance together with effects of spin- accumulation without invoking long range pairing correlations in the ferromagnet.

cond-mat.supr-con↗
arXiv2000

Finite-element theory of transport in ferromagnet-normal metal systems

We formulate a theory of spin dependent transport of an electronic circuit involving ferromagnetic elements with non-collinear magnetizations which is based on the conservation of spin and charge current. The theory considerably simplifies the calculation of the transport properties of complicated ferromagnet-normal metal systems. We illustrate the theory by considering a novel three terminal device.

cond-mat.mes-hall↗
arXiv1999

Negative Domain Wall Resistance in Ferromagnets

The electrical resistance of a diffusive ferromagnet with magnetic domain walls is studied theoretically, taking into account the spatial dependence of the magnetization. The semiclassical domain wall resistance is found to be either negative or positive depending on the difference between the spin-dependent scattering life-times. The predictions can be tested experimentally by transport studies in doped ferromagnets.

cond-mat.mes-hall↗
arXiv1999

Scattering theory of the Johnson spin transistor

We discuss a simple, semiclassical scattering theory for spin-dependent transport in a many-terminal formulation, with special attention to the four terminal device of Johnson referred to as spin transistor

cond-mat.mes-hall↗
arXiv1999

Ballistic and diffuse transport through a ferromagnetic domain wall

We study transport through ballistic and diffuse ferromagnetic domain walls in a two-band Stoner model with a rotating magnetization direction. For a ballistic domain wall, the change in the conductance due to the domain wall scattering is obtained from an adiabatic approximation valid when the length of the domain wall is much longer than the Fermi wavelength. In diffuse systems, the change in the resistivity is calculated using a diagrammatic technique to the lowest order in the domain wall scattering and taking into account spin-dependent scattering lifetimes and screening of the domain wall potential.

cond-mat.mes-hall↗
arXiv1998

Non-equilibrium spin accumulation in ferromagnetic single-electron transistors

We study transport in ferromagnetic single-electron transistors. The non- equilibrium spin accumulation on the island caused by a finite current through the system is described by a generalized theory of the Coulomb blockade. It enhances the tunnel magnetoresistance and has a drastic effect on the time- dependent transport properties. A transient decay of the spin accumulation may reverse the electric current on time scales of the order of the spin-flip relaxation time. This can be used as an experimental signature of the non- equilibrium spin accumulation.

cond-mat.mes-hall↗
arXiv1998

Spin-accumulation in small ferromagnetic double barrier junctions

The non-equilibrium spin accumulation in ferromagnetic double barrier junctions is shown to govern the transport in small structures. Transport properties of such systems are described by a generalization of the theory of the Coulomb blockade. The spin accumulation enhances the magnetoresistance. The transient non-linear transport properties are predicted to provide a unique experimental evidence of the spin-accumulation in the form of a reversed current on time scales of the order of the spin-flip relaxation time.

cond-mat.mes-hall↗
arXiv1998

Ballistic electron transport through magnetic domain walls

Electron transport limited by the rotating exchange-potential of domain walls is calculated in the ballistic limit for the itinerant ferromagnets Fe, Co, and Ni. When realistic band structures are used, the domain wall magnetoresistance is enhanced by orders of magnitude compared to the results for previously studied two-band models. Increasing the pitch of a domain wall by confinement in a nano-structured point contact is predicted to give rise to a strongly enhanced magnetoresistance.

cond-mat.mes-hall↗
arXiv1997

Light scattering from a periodically modulated two dimensional electron gas with partially filled Landau levels

We study light scattering from a periodically modulated two dimensional electron gas in a perpendicular magnetic field. If a subband is partially filled, the imaginary part of the dielectric function as a function of frequency contains additional discontinuities to the case of completely filled subbands. The positions of the discontinuities may be determined from the partial filling factor and the height of the discontinuity can be directly related to the modulation potential. The light scattering cross section contains a new peak which is absent for integer filling.

cond-mat.mes-hall↗
arXiv1997

Spin-density and charge-density excitations in quantum wires

We study an interacting electron gas in a quantum wire within the Hartree-Fock random phase approximation. Vertex corrections to the electron spin polarizability due to the electronic exchange interaction are important giving rise to spin-density excitations (SDE) with large oscillator strength shifted to lower energies with respect to single-particle states. The energy of intersubband SDE oscillates with the number of subbands occupied and has a minimum when a subband energy is close to the chemical potential. Intrasubband SDE have a linear dispersion at small wave-vectors. The corresponding sound velocity is reduced with respect to the Fermi velocity due to exchange interaction within the occupied subbands and exchange screening caused by virtual transitions to upper subbands. For intersubband and intrasubband charge-density excitations (CDE) vertex corrections are of less importance. For only a single subband occupied the screening of CDE and SDE in the Tomonaga-Luttinger model due to virtual transitions to upper subband is studied, where the virtual transitions are treated within the Hartree-Fock approximation. The calculations are in good qualitative agreement with experiments.

cond-mat.mes-hall↗
arXiv1996

The effects of compressible and incompressible states on the FIR-absorption of quantum wires and dots in a magnetic field

We investigate the effects of compressible and incompressible states on the FIR-absorption of quantum wires and dots in a homogeneous perpendicular magnetic field. The electron-electron interaction is treated in the Hartree approximation at a finite low temperature. The calculated dispersion of the collective excitations reproduces several experimental results.

cond-mat↗
arXiv1996

Collective Excitations in Realistic Quantum Wires

We have used the Hartree-Fock Random Phase Approximation (HF-RPA) to study the interacting electron gas in a quantum wire. The spectra of intersubband spin-flip excitations reveal a considerable red shift with respect to single-particle HF energies. That signals on appearance of collective intersubband spind-density excitations due to the exchange interaction. The long wavelength dispersions of the intrasubband collective spin-density excitations are linear, but the sound velocities are renormalised due to the exchange interaction and screening. The in-phase intrasubband charge-density excitation has the long wavelength form $q[-\ln(q)]^{1/2}$. We found good qualitative agreement of our results with experimental observations.

cond-mat↗