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

P. GIUDICI; A. R. GOÑI; C. THOMSEN

Berlin

Congreso; Fr¨uhjahrstagung der deutschen physikalischen Gesellschaft; 2005

High-mobility two-dimensional electron gases (2DEG) realized inmodulation-doped GaAs single quantum well (SQW) structures are particularlysuitable for studies of the many-body behavior of dilute electronsystems. Recently, we have shown that a 2DEG undergoes a first-orderphase transition when the first-excited subband becomes populated.Furthermore, the occurrence of a spontaneous breakdown of the spinsymmetry was predicted, leading to the formation of a ferromagneticphase. The existence of the spin instability was confirmed by PL andinelastic light scattering experiments at low effective temperatures ofthe electron gas. In this work we investigate the dependence of thephenomenology of the exchange instability on the SQW-width. For thispurpose we studied the emission spectra of three SQW samples whichdiffer only in the well width (20, 25 and 30 nm). The renormalizationenergy of the spin-polarized phase presents a clear trend for the studiedQW widths. This dependence on well thickness indicates that thestrength of the exchange interactions is a function of the confinement ofthe electron wave functions.