Archive for the ‘2011’ Category

Posted by Kenneth Burch On October - 4 - 2011 Comments Off on Infrared probe of the insulator-to-metal transition in Ga1−xMnxAs and Ga1−xBexAs

We report infrared studies of the insulator-to-metal transition (IMT) in GaAs doped with either magnetic (Mn) or nonmagnetic acceptors (Be). We observe a resonance with a natural assignment to impurity states in the insulating regime of Ga1−xMnxAs, which persists across the IMT to the highest doping (16%). Beyond the IMT boundary, behavior combining insulating and metallic trends also persists to the highest Mn doping. Be-doped samples, however, display conventional metallicity just above the critical IMT concentration, with features indicative of transport within the host valence band.   B. C. Chapler, R. C. Myers, S. Mack, A. Frenzel, B. C. Pursley,  [ Read More ]

Posted by Kenneth Burch On June - 24 - 2011 Comments Off on Fabrication and characterization of topological insulator Bi2Se3 nanocrystals

In the recently discovered class of materials known as topological insulators, the presence of strong spin-orbit coupling causes certain topological invariants in the bulk to differ from their values in vacuum. The sudden change in invariants at the interface results in metallic, time reversal invariant surface states whose properties are useful for applications in spintronics and quantum computation. However, a key challenge is to fabricate these materials on the nanoscale appropriate for devices and probing the surface. To this end we have produced 2 nm thick nanocrystals of the topological insulator Bi2Se3 via mechanical exfoliation. For crystals thinner than 10 nm  [ Read More ]