Berlin 2015 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 106: Transport, magnetotransport and quantum Hall physics
HL 106.7: Talk
Friday, March 20, 2015, 11:45–12:00, EW 202
Impurity induced phase transition in GaAs/AlGaAs two-dimensional electron gas — •Eddy P. Rugeramigabo, Lina Bockhorn, and Rolf J. Haug — Institute for Solid State Physics, Dep. Nanostructures, Leibniz Universität Hannover
A phase transition is observed at high magnetic fields in a two-dimensional electron gas (2DEG). The 2DEG is realized in a modulation Si-doped GaAs/AlGaAs quantum well (QW). Additionally, Si atoms were homogeneously incorporated in the GaAs QW layer. Here, they act as impurities. The 2DEG has an electron density of ne = 3.2·1011cm−2 and a mobility of µe = 1.2·105cm2/Vs.
We performed magnetotransport measurements between 30mK and 900mK. Magnetic field sweeps above 6.6T induce a phase transition at temperatures T<600mK. After the transition, we observe at low magnetic fields the formation of beating features in the Shubnikov-de Hass oscillations. At high magnetic fields, fractional filling factors between ν=2 and ν=1 become more developed.
The new phase has a metastable equilibrium at magnetic fields between 7T and 13T (2<ν<1). Such a metastable state of the 2DEG was also reported by Kukushkin et al.[1], but for magnetic field range of 1<ν<1/2. We attribute our observations to a change in the scattering potential of the impurity states within the 2DEG. This can be e.g. frozen spin polarization caused by high magnetic fields at low temperatures.
[1] I. V. Kukushkin, et al., Phys. Rev. B 51, 18045 (1995)