Exchange-drive instability and spin polarization of the two-dimensional electron gas at zero magnetic field

P. GIUDICI; A. R. GOÑI; C. THOMSEN

Erice

Workshop; Quantum Phase at the nanoscale; 2002

In this work we show that at low temperature and zero magnetic field a 2D electron gas formed in a single GaAs quantum well (SQW) undergoes a first-order phase transition, as the first excited electron subband becomes populated with electrons by raising the Fermi level with a gate voltage between two contacts at the top and the back surface of the samples. The evidence is found in the abrupt renormalization of the energy of the first excited subband and its sudden population, as determined from photoluminescence (PL) and inelastic light scattering measurements. Self-consistent density-functional calculations with exact exchange potential for a 2D electron system reveal that this transition is driven by intersubband exchange interactions which provide a feedback mechanism for charge transfer into the excited subband. This novel theory further predicts the first-order character of the transition. In fact, experiments performed at different temperatures indicate the existence of a critical point at around 35 K.