Zheng-Chuan Wang

Spin tunneling in ferromagnet–insulator–ferromagnet junctions

Abstract We have applied Buttikers gauge invariant, charge conserving dc transport theory to investigate the spin-polarized tunneling in ferromagnet–insulator–ferromagnet junctions at finite temperatures. It is observed that the spin polarization direction and temperature have remarkable effects on the differential conductance as well as the derivative of the conductance. At low temperatures the quantum resonant tunneling is dominant, while the thermal activated process plays a great role at high temperatures. A so-called spin-valve phenomenon is clearly seen at low temperatures. The results for asymmetric and symmetric junctions differ. The quantum electrochemical capacitance for such a junction is also calculated. Our findings are expected to be confirmed experimentally.

Spinor Boltzmann-Poisson equation and application to spin-dependent transport in magnetic multilayers

In order to consider the effect of electron-electron (e-e) interactions on the quantum transport in magnetic multilayers, the spinor Boltzmann equation and Poisson equation are jointly investigated. The analytical expressions of the spinor distribution function and the self-consistent average potential associated with e-e interactions are obtained, and the dielectric function in the self-consistent average potential is naturally generalized. Then we apply these results to the system of ferromagnet/insulator/dilute-magnetic-semiconductor (FM/I/DMS) layers, and study the time and position dependences of the charge current, spin current and spin accumulation in the FM/I/DMS system.

The effect of the geometric phase on spin-polarized electron tunnelling

In order to explore the effect of the geometric phase on the spin-polarized electron tunnelling in a ferromagnet/insulator/ferromagnet (FM/I/FM) junction, in this paper, we apply a voltage drop in the insulating layer and allow it to vary adiabatically with time t. Then the wavefunction will acquire a geometric phase which will give rise to an observable effect on the physical quantities of interest. The numerical results indicate that the geometric phase certainly has an influence on the differential conductance and the tunnelling magnetoresistance (TMR) in the spin-polarized tunnelling. We also show results for the conductance and TMR obtained by changing the orientation angle and the magnitude of the molecular field in the ferromagnets. An experimental profile for observing the effect of the geometric phase on the spin-polarized electron transport in a FM/I/FM tunnel junction is suggested.

ELECTRON–ELECTRON INTERACTIONS IN THE QUANTUM DOT INDUCED BY THE SURFACE ACOUSTIC WAVE

In order to study the higher order quantized plateaus in the acoustoelectric current induced by the surface acoustic wave (SAW), we consider in this paper, the Coulomb interaction of electrons trapped in the SAW-induced quantum dot at the Hartree approximation level. The Hartree self-consistent potential that originates from the electron–electron interactions in the quantum dot satisfies the Poisson equation and can be solved numerically together with the Schrodinger equation; following which, the conventional tunneling mechanism can be used to interpret the step-like acoustoelectric current, in which the escape of electrons from the quantum dot determines the deviation of the current from the quantized value. It should be noted that the quantum dot is formed by both the SAW-induced potential and the Hartree self-consistent potential in our paper, which is different from previous works. We have also calculated the first and the second quantized plateaus by use of this method.