Correlated Electron Surface State in SmB6Zachary Fisk, University of California- Irvine, DMR 0801253

The electrical resistance of cubic SmB6 (with structure shown in the figure) increases 4 orders of magnitude on cooling to 2K from room temperature, corresponding to the opening of a semiconducting gap which becomes fully formed below 4K. The resistivity becomes constant at lowest temperature, apparently due to formation of a surface metallic state. The non-linear voltage-current curves at upper right obtained at differing sample base temperatures are the result of self heating of the sample from the current, but are coupled with an intrinsic sample time- dependent relaxation arising from a giant capacitance developing coincident with the surface state. This leads to the oscillatory behavior at constant current drive, shown in the second slide.

Correlated Electron Surface State in SmB6Zachary Fisk, University of California- Irvine, DMR 0801253

At sample base temperature of 2K a constant dc voltage applied across the SmB6 crystal (gray-blue in upper figure) drives oscillations with frequency proportional to current, rather than driving the circuit to a fixed temperature end point. The encoding by frequency of the drive current is closely analogous to the response of a nerve axion to applied stimulus. The gap structure in SmB6 derives from hybridization of Sm 4f-levels with conduction electron bands. It is hypothesized that this material is a topological insulator, which as such has a conducting surface state. This opens a new direction in correlated electron physics as well as offering a possible venue for quantum computing.