One of the longest-studied mixed valent insulators, Samarium Hexaboride (SmB6), exhibits a mysterious residual resistivity at low temperatures (T < 4 K), but at a value too high to explain within the framework of bulk conduction [1]. All efforts over the years to eliminate this resistivity have failed. The recently conjectured existence of a topologically protected surface state in SmB6 [2] could resolve the long-standing mystery surrounding its low- temperature transport properties.
We developed a novel configuration designed to distinguish bulk-dominated conduction from surface-dominated conduction by exaggerating the geometric differences between the two conduction paths through contacts placed on both sides of a thin sample. The results of this experiment show that below 3 K, SmB6 has a fully-insulating bulk and an intrinsic metallic surface with a remarkably high conductivity [3]. We argue that the robustness of the surface conductivity is a signature of the topological protection of the surface states. This discovery resolves the old mystery about the strange transport behavior of this material, and it provides a material in which 2D transport properties of a true topological state can be studied. I will also present some of our results from transport experiments using a Corbino geometry.
[1] J. W. Allen, B. Batlogg and P. Wachter, Phys. Rev. B 20, 4807 (1979).
[2] M. Dzero, K. Sun, V. Galitski and P. Coleman, Phys. Rev. Lett.
104, 106408 (2010).
[3] S. Wolgast, Ç. Kurdak, K. Sun, J. W. Allen, D. J. Kim and Z. Fisk, arXiv:1211.5104v2.
In collaboration with Steven Wolgast, Yun Suk Eo, Kai Sun, James W.
Allen, Dae-Jong Kim, and Zachary Fisk.
