Exchange instability of the two-dimensional electron gas in semiconductor single quantum wells

P. GIUDICI; A. R. GOÑI; C. R. PROETTO; F. A. REBOREDO; F. GUINEA

Mauterndorf

Congreso; International Winter school on low dimensional systems; 2004

<!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:1; mso-generic-font-family:roman; mso-font-format:other; mso-font-pitch:variable; mso-font-signature:0 0 0 0 0 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} p.MsoBodyText, li.MsoBodyText, div.MsoBodyText {mso-style-noshow:yes; mso-style-unhide:no; mso-style-link:"Textkörper Zchn"; margin:0cm; margin-bottom:.0001pt; text-align:justify; text-indent:21.3pt; mso-pagination:widow-orphan; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} span.TextkrperZchn {mso-style-name:"Textkörper Zchn"; mso-style-noshow:yes; mso-style-unhide:no; mso-style-locked:yes; mso-style-link:Textkörper; mso-ansi-font-size:12.0pt; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt;} @page WordSection1 {size:612.0pt 792.0pt; margin:70.85pt 70.85pt 2.0cm 70.85pt; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.WordSection1 {page:WordSection1;} --> 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.