Metal-insulator transition at B=0 in an ultra-low density ($r_s=23$) two dimensional GaAs/AlGaAs hole gas

Abstract

We have observed a metal-insulator transition in an ultra-low density two dimensional hole gas formed in a high quality GaAs-AlGaAs heterostructure at B=0. At the highest carrier density studied ($p_s=2.2x10^{10}c{m}^{-2},r_s=16$) the hole gas is strongly metallic, with an exceptional mobility of $425,000c{m}^2{V}^{-1}{s}^{-1}$. The low disorder and strength of the many-body interactions in this sample are highlighted by the observation of re-entrant metal insulator transitions in both the fractional ($\nu <1/3$) and integer ($2>\nu >1$) quantum Hall regimes. On reducing the carrier density the temperature and electric field dependence of the resistivity show that the sample is still metallic at $p_s=1.3x10^{10}c{m}^{-2}$ ($r_s=21$), becoming insulating at $p_s\simeq 1x10^{10}c{m}^{-2}$. Our results indicate that electron-electron interactions are dominant at these low densities, pointing to the many body origins of this metal-insulator transition. We note that the value of $r_s$ at the transition ($r_s=23+/-2$) is large enough to allow the formation of a weakly pinned Wigner crystal, and is approaching the value calculated for the condensation of a pure Wigner crystal.

4 pages, latex, 4 postscript figures, submitted to EP2DS-12 on 21st August 1997, to appear in Physica B

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• On the metallic behaviour in dilute two-dimensional systems
• Phase diagram of the metal-insulator transition in 2D electronic systems
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