Speaker
Simon Davenport
(University of Oxford)
Description
In this talk we will discuss fractional quantum Hall physics
occurring when the spin of the electrons is not fully
polarised. This physics has been the focus of much recent
theoretical work aiming to expanding the possibilities of
realising non-abelian quantum Hall states in situations
where the spin is non-polarised, such as the non-abelian
spin singlet (NASS) state. Spin non-polarised FQHE physics
has also spawned much recent experimental work on GaAs
quantum well structures, with particular interest for
fractions in the 2nd LL. To illustrate the ideology we shall
recall some earlier experiments done by Kukushkin's group
which investigates ``spin-transitions"---transitions
between FQHE states having different net spin polarisations
as a function of the ratio of Zeeman to Coulomb energy---in
GaAs heterojunctions and for fractions in the LLL. We shall
then describe some numerical work that we have conducted
in order study the spin transitions from a theoretical
perspective, based on composite fermion (CF) theory. Our
work builds on some earlier work by Park and Jain, which
we extend to encompass the negative effective field case
describing filling fractions 2/3, 3/5 and 4/7. We will also
present some predictions of CF theory for spin transitions in
the 2nd LL at filling fractions 8/3, 13/5 and 18/7, the 8/3
case being the subject of recent experiments by Pan et al..
Time permitting, we shall discuss an ongoing project which
is to investigate the theoretical possibility of engineering the
NASS state at filling factor 4/7 in the LLL or 18/7 in the 2nd
LL.
