Metallic Behavior and the Metal-Insulator Transition in Strongly Correlated 2D Holes – Xuan Gao

Date: Thu. February 7th, 2008, 4:15 pm-5:15 pm
Location: Rockefeller 301

The celebrated scaling theory of localization asserted that all two- dimensional (2D) Fermionic systems are insulators. However, experiments in the 1990’s have revealed an intriguing metallic state and metal-insulator transition in various 2D semiconductor systems, where the carriers are strongly correlated. It is still being debated that if this 2D metallic state is a new electronic state of matter stabilized by strong Coulomb interactions. We have studied electrical transport properties of strongly interacting 2D holes in the world’s cleanest Gallium Arsenide quantum well samples down to ultra-low temperatures (T ~ 0.01K). We found that removing the spin degree of freedom (by applying a magnetic field parallel to the 2D plane) gradually drives the system back to the conventional ‘Fermi liquid’ state described by the scaling theory of localization. This experiment suggests that spin-degeneracy is critical in the formation of the 2D metallic state. We also discovered that there is a remarkable order of magnitude enhancement in the hole-phonon coupling in our correlated 2D hole system.