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
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.
Host: Albert Chang