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Physics Special Colloquium, February 24, 2005The 2D metallic state and metal-insulator transition: two decades of controversyXuan GaoLos Alamos National LaboratoryThe celebrated scaling theory of localization predicts that there is no true metallic ground state for disordered Fermi liquids in two dimensions (2D) in zero magnetic field. However, experiments in early 1990’s have revealed an intriguing metallic state and metal-insulator transition in various low density 2D systems. For these systems, carriers are strongly correlated, as characterized by the large value of rs, the ratio between Coulomb interaction energy and the Fermi energy EF. It is currently being debated that if the strong correlations can stabilize a metallic non-Fermi liquid phase in 2D. In this talk I will present transport experiments on dilute 2D holes with rs >20 in some world highest quality Gallium Arsenide (GaAs) quantum wells down to temperatures as low as 0.01K. We find that a small parallel magnetic field (B||) suppresses the strength of the 2D metallicity without affecting its energy scale. In strong B|| when the spins are all polarized, we observe a logarithmically diverging resistance of 2D holes at low T, as predicted by the scaling theory of localization, indicating the system is driven back to the Fermi liquid state. These experiments show that the 2D metallic behavior is closely related to the spins of the carriers. I will also discuss our recent observation of strongly enhanced hole-phonon coupling in dilute 2D GaAs hole system. References: X. P.A. Gao et al., Phys. Rev. Lett., 88, 166803 (2002); ibid 89, 016801 (2002); ibid 93, 256402 (2004); cond-mat/0501686, to appear in PRL (2005). 10:30 a.m., Room 1094 Smith LabRefreshments served at 10:00 a.m. |
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