Dependence on Well Width of the Exchange Instability in Dilute 2D Electron Gases

P. GIUDICI; A. R. GOÑI; C. THOMSEN

Cancún

Conferencia; International Conference in Low Dimensional Structures and Devices; 2004

High-mobility two-dimensional electron gases (2DEG) realized in modulationdopedGaAs single quantum well (SQW) structures are particularly suitablefor studies of the many-body behavior of dilute electron systems. Recently, wehave shown that a 2DEG undergoes a rst-order phase transition, when therst-excited subband becomes populated. Evidence was found in the abruptrenormalization of the subband energy and its sudden occupation, as determinedfrom photoluminescence 1 and Inelastic light scattering 2 measurements.Self-consistent density functional calculations including the exact exchange potentialfor the 2DEG demonstrated that this thermodynamical instability isa consequence of intersubband exchange-energy terms of the Coulomb interaction.The theory further predicted the occurrence of a spontaneous breakdownof the spin symmetry without magnetic eld, leading to the formationof spin-polarized domains in the rst excited subband. The existence of thespin-polarized phase was conrmed by PL and inelastic light scattering experimentsat low eective temperatures of the electron gas 3. In this work weinvestigate the dependence of the phenomenology of the exchange instabilityon the width of the SQW. For this purpose we studied the emission spectraof three SQW samples which dier only in the well width (20, 25 and 30 nm).The abruptness of the renormalization of the intersubband energy at the transitionas the conditions for the stability of the spin-polarized phase presenta clear trend for the studied QW widths. This dependence on well thicknessindicates that the strength of the exchange interactions is a function of theconnement of the electron wave functions.