Berlin 2008 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 46: Transport in high magnetic field/quantum-Hall-effect
HL 46.2: Vortrag
Donnerstag, 28. Februar 2008, 12:00–12:15, EW 202
quantum hall ferromagnetism in graphene: SU(4) bosonization approach — •ricardo doretto1,2 and cristiane morais smith2 — 1Institut feur Theoretische Physik, Universitaet zu Koeln, Koeln, Germany — 2Institute for Theoretical Physics, Utrecht University, Utrecht, The Netherlands
We study the quantum Hall effect in graphene at filling factors ν = 0 and ν = ± 1, concentrating on the quantum Hall ferromagnetic regime, within a non-perturbative bosonization formalism. We start by developing a bosonization scheme for electrons with two discrete degrees of freedom (spin-1/2 and pseudospin-1/2) restricted to the lowest Landau level. Three distinct phases are considered, namely, the spin-pseudospin, spin, and pseudospin phases. The first corresponds to a quarter-filled (ν =−1) while the others to a half-filled (ν = 0) lowest Landau level. In each case, we show that the elementary neutral excitations can be treated approximately as a set of n-independent kinds of boson excitations. We then apply the formalism to an effective continuous model proposed by Alicea and Fisher. For each quantum Hall state, an effective interacting boson model is derived and the dispersion relations of the elementary excitations are analytically calculated. We propose that the charged excitations (skyrmions) can be described as a coherent state of bosons. We calculate the semiclassical limit of the boson model derived from the SU(4) invariant part of the original fermionic model and show that it agrees with the results of Arovas et-al. for SU(N) quantum Hall skyrmions. We briefly discuss the influence of the SU(4) symmetry breaking terms in the skyrmion energy.