F. M. Souza

Spin-dependent ringing and beats in a quantum dot system

We report spin-dependent quantum coherent oscillations (ringing) and beats of the total and the spin currents flowing through a quantum dot with Zeeman split levels. The spin-dependent transport is calculated via nonequilibrium Green function in the transient after a bias voltage is turned on at

Transient Charging and Discharging of Spin-polarized Electrons in a Quantum Dot

t=0

Spin-polarized STM for a Kondo adatom

. The dot is coupled to two electrodes that can be ferromagnetic or nonmagnetic. In the ferromagnetic case both parallel and antiparallel alignments are considered. The coherent oscillation and beat frequencies are controlled via the Zeeman energy

Optical spectra of a quantum dot in a microcavity in the nonlinear regime

{E}_{Z}

Scanning tunneling microscope operating as a spin diode

. In particular, for

Spin polarized transport driven by square voltage pulses in a quantum dot system

{E}_{Z}=0

Fano–Kondo spin filter

no beats are observed and the spin current is zero for nonmagnetic leads. In the ferromagnetic case a finite spin current is found for

Light emission and current rectification in a molecular device: Experiment and theory

{E}_{Z}=0

Nonequilibrium transport in a quantum dot attached to a Majorana bound state

. The effects of temperature are also analyzed. We observe that with increasing temperature the ringing response and the beats tend to disappear. Additionally, the spin current goes to zero for nonmagnetic leads, remaining finite in the ferromagnetic case. The tunnel magnetoresistance also reveals quantum coherent oscillations and beats, and it attains negative values for small enough temperatures and short times.

Shot Noise in a Spin-Diode Geometry

Laboratory of Physics, Helsinki University of Technology, P. O. Box 1100, FI-02015 HUT, Finland(Date: February 1, 2008)We study spin-polarized transient transport in a quantum dot coupled to two ferromagnetic leadssubjected to a rectangular bias voltage pulse. Time-dependent spin-resolved currents, occupations,spin accumulation, and tunneling magnetoresistance (TMR) are calculated using both nonequilib-rium Green function and master equation techniques. Both parallel and antiparallel leads’ mag-netization alignments are analyzed. Our main findings are: a dynamical spin accumulation thatchanges sign in time, a short-lived pulse of spin polarized current in the emitter lead (but not in thecollector lead), and a dynamical TMR that develops negative values in the transient regime. Wealso observe that the intra-dot Coulomb interaction can enhance even further the negative values ofthe TMR.