Electronic states in externally modulated dilute magnetic semiconductor/superconductor hybrids

Abstract

Dilute magnetic semiconductors (DMSs) are attractive. They are candidate materials for applications in novel spintronic devices. Because of the giant Zeemaneect in the paramagnetic state, a magnetic eld can be used to manipulate the spin and charge of carriers in DMSs. One possibility is to exploit the nonhomogeneous magnetic elds due to superconductors. In this thesis, the heterostructures of the planar DMS and superconductors in dierent geometries and superconducting states are investigated to understand the electronic structure of electrons in the DMS.The combination of a superconducting disk in the Meissner state and the planarDMS is studied using both simple and realistic models of the magnetic eldassociated with the disk. The giant Zeeman interaction is found to substantiallyinuence the energies of magnetically conned states in the adjacent DMS. In thesimple model eld, the giant Zeeman energy acts as an extra conning potentialand results in spin dependent electron states exhibiting dierent spatial distributions, while the more realistic model eld results in conned states exhibiting a variety of mixed spin characters.The hybrid of a superconducting lm in a superconducting vortex state andthe DMS is then explored. The concentrated magnetic eld due to an isolatedvortex is shown to trap strongly spin polarised electron states. In the case ofan Abrikosov lattice of vortices, interactions between vortex-bound states resultin a band structure which can be controlled by the magnitude of an externaluniform magnetic eld. It is found that the numerical band structures obtainedusing a basis of Landau states dier from those previously reported, leading tothe development of a tight-binding theory to conrm their corrections. Anotherhybrid investigated is a square superconductor above the DMS. In this case, thearrangement of vortices is distorted by the boundary of the sample, leading to the possibility of multivortex state and/or giant vortex states. It is discovered thatthe magnetic eld due to the former state induces \molecular" electron statesin the DMS, while that due to the latter state induces electron states with increased spatial distribution. Tight-binding theory is again used to describe theobserved energy levels and the interactions between electron states induced bythe magnetic elds due to separated vortices in the multivortex state.

Date of Award	30 Sept 2012
Original language	English
Awarding Institution	University of Bath
Supervisor	Simon Crampin (Supervisor)