Metal–insulator transition at B=0 in an ultra-low density two-dimensional hole gas

• Published in: Physica. B, Condensed matter Condensed matter, 1998-06, Vol.249, p.705-709
• Main Authors: Simmons, M.Y, Hamilton, A.R, Griffiths, T.G, Savchenko, A.K, Pepper, M, Ritchie, D.A
• Format: Article
• Language: English
• Subjects: Metal–insulator transitions; Two-dimensional hole systems; Wigner solid
• ISSN: 0921-4526; 1873-2135
• DOI: 10.1016/S0921-4526(98)00296-8

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 =2.2×10 10 cm −2 , r s=16) the hole gas is strongly metallic, with an exceptional mobility of 425 000 cm 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 ( ν< 1 3 ) and integer (2> ν>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 =1.3×10 10 cm −2 ( r s=21), becoming insulating at p s ≃1×10 10 cm −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 approaches the value calculated for the condensation of a pure Wigner crystal.