Exchange-driven instability and spin polarization of the two-dimensional electron gas

P. GIUDICI; A. R. GOÑI; U. HABOECK; C. THOMSEN; K. EBERL; F. A. REBOREDO; C. R. PROETTO

Edimburgh

Conferencia; International Conference on the Physics of Semiconductors (ICPS 26); 2002

We show that at low temperature and zero magnetic field a two-dimensional (2D)electron gas formed in a GaAs single quantum well undergoes a first-order phase transition, as the first excited electron subband becomes populated with electrons by rising the Fermi level using a dc voltage. 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) 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. This theory also predicts the spontaneous breakdown of the spin symmetry at the phase transition without magnetic field. In fact, PL spectra measured at 2 K and with very low laser powers exhibit a new peak below the energy of the optical transition from the first excited subband, which is associated with the spin-polarized phase