Date of Award

12-2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Theoretical Physics

Advisor

Marinescu, Catalina

Committee Member

Manson , Joseph R

Committee Member

Ke , Pu-Chun

Committee Member

Sosolik , Chad

Abstract

We discuss the existence of spin instabilities and of possible ground states with broken spin symmetry in the presence of a tilted magnetic field for several semiconductor heterostructures. In each instance, the fundamental premise of our study is the existence of a spin degeneracy, controlled by tuning various experimentally controllable parameters, that permits the apparition of spin-flip processes driven entirely by the many-body Coulomb interaction. If in the case of a single quantum well, the spin instabilities trigger an abrupt paramagnetic to ferromagnetic phase transition, we demonstrate that in superlattices, at low temperatures, a stable spin density wave ($SDW$) ground state is supported for certain system parameters that allow a substantial overlap of the opposite spin interbands when the electron-electron interaction is considered within the Hartree-Fock approximation. In our study, we consider two different types of superlattices that present both spin instabilities that involve electrons from different Landau levels, as well as from the same, lowest Landau level. In each case, we solve the SDW gap equation numerically through an iterative procedure and study the dependence of the solution on the relevant system parameters. Our numerical estimates indicate that in the SDW ground state, the systems present a sizable spin polarization that is entirely controllable by external means, generating possible spintronics applications.

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