| Spintronics is a new kind of technique, which makes use of magnetic moment of electrons instead of charge. Its main purpose is to create devices based on the spin of electrons. Compared with traditional semi-conductor devices, they are particularly attractive for their better stability,higher speed in data processing,lower power exhaust,higher integration density and so on. Among the necessary elements for spin-based devices is the generation of spin current. Now the most frequent devices that can be used to produce spin current is mesoscopic quantum dot system, because it has a lot of advantages. For example, in mesoscopic quantum dot system, Electronic spin freedom have relatively long decoherence time, electrons can be easily manipulated etc.Using the method of density matrix, we get the rate equations about electron transport in the mesoscopic system derived form many body schrodinger equation. Makeing using of them, we obtain the spin current and charge current through the systems. The result has shown that when the positions of left and reservoirs Fermi levels are same, we can make the chagre current zero throught the quantum dot and only spin current exist by adjusting the possibility of electrons tunnelling into or out of quantum dot. This is an important property in the spintronics, because what makes spin devices work is spin current. In addition, we get the connection of spin current throught the quantum dot and the Rabi frequency of oscillating magnetic field and find that the spin current decrease with spin decoherence time; It is discovered that when there is bias between the left and right reservoirs, we can get the condition of system with only charge current. In the last part, we analyze the influence of spin flip on the spin current through the system, discovering that the spin flip could enhance the spin current .Using the method of Fermi-Dirac distribution, we can consider the Coulomb blockade in the quantum dot. This work is in progress at present.
|
PDF Full Text Request