Condensed Matter Seminar Series

Spin Effects in One Dimensional Electronic Conduction

Sir Michael Pepper

University College London

Thursday May 17,  11:00 am,  Room 298,  Physics Building

Abstract: Our recent results are presented on the role of spin in electron transport in quasi-one dimensional channels in the GaAs-AlGaAs heterostructure. In the regime of strong confinement, the conductance takes on quantized values given by 2ne²/h where n is the number of one dimensional subbands. Lifting the momentum degeneracy, with a source-drain voltage, results in structure appearing at 0.25 and 0.85, in units of 2e²/h, indicating a lifting of the spin degeneracy as well. This conclusion is supported by detailed measurements of the dc conductance and effects of application of a magnetic field. It will be shown that a range of other transport measurements supports this conclusion.
        When the confinement potential decreases, the electron wavefunctions relax in the second dimension. In order to minimise the electron-electron repulsion, an array is formed in which a two row configuration becomes the ground state and is the prelude to formation of a Wigner Lattice. The rows can be separate but as they are forced back together hybridization can be observed prior to the formation of a single row. As these transitions occur a range of spin effects can be observed.
        In the low carrier concentration limit the exchange energy between neighbouring electrons becomes less than kT and the spin direction can no longer be defined. This spin incoherent regime has been investigated and will be discussed.