Toward Perfect 1D Conduction in Magnetic Topological Insulators: Nano Seminar Series

Seminar | October 19 | 2-3 p.m. | 390 Hearst Memorial Mining Building

 Prof. David Goldhaber-Gordon, Stanford University, Physics

 Berkeley Nanosciences and Nanoengineering Institute

I will explain what is "perfect" 1D conduction and describe several strategies for achieving it. Some require high magnetic fields and/or cryogenic temperatures, but there's now hope of achieving perfect 1D conduction at room temperature with no external magnetic field, through a phenomenon known as the quantum anomalous Hall effect.

This effect was recently realized in thin films of Cr-doped (Bi, Sb)2Te3, a ferromagnetic 3D topological insulator. The presence of ferromagnetic exchange breaks time-reversal symmetry, opening a gap in the surface states, but gives rise to dissipationless chiral conduction at the edge of a magnetized film. Ideally, this leads to vanishing longitudinal resistance, and Hall resistance roughly h/e^2 , where h is Planck's constant and e is the electron charge (this is a signature of one type of perfect 1D conduction). But perfect quantization had proved elusive.

I'll show results on the QAHE in the limit of zero applied magnetic field, and measure Hall resistance quantized to within two parts per 10 million. This result demonstrates a significant step toward achieving dissipationless electron transport in technologically relevant conditions. I’ll also discuss how we can manipulate where this conduction occurs by modifying the magnetic domain structure.
David Goldhaber-Gordon did his PhD in Physics at MIT (1999), postdoc at Harvard, and joined Stanford in 2001, where he has directed their NSF NSEC and other centers. Awards include the APS' Valley Prize, the McMillan award, and several young investigator fellowships for condensed matter research.