Topological Kondo insulators: strong correlations meet topology

Onur Erten,

Department of Physics and Astronomy, Rutgers University, Piscataway, NJ, 08854, USA

The electrons in heavy fermion materials experience strong spin-orbit coupling, with mutual  interactions that greatly exceed their kinetic energy. It has long been known that the spin orbit coupling stabilizes new kinds of heavy fermion metals, superconductors and Kondo insulators. In this talk I will discuss the recent realization that spin orbit can also drive new kinds of topological order. I will mainly focus on SmB6  and CeNiSn. Motivated by the observation of light surface states of SmB6, I will first introduce the concept of  `Kondo breakdown' which we believe is taking place at the surfaces.  I will present both numerical and analytic results which show that the decoupling of the localized moments at the surface disturbs the compensation between light and heavy electrons on the surface. Dispersion of these uncompensated surface states gives rise to much lighter quasiparticles in accordance with ARPES experiments[1]. Another tantalizing result about SmB6 derives from recent quantum oscillation experiments which lead to completely controversial interpretations. I will discuss these new results from a general theoretical viewpoint considering both bulk and surface scenarios and our new interpretation in terms of Kondo break-down in topological surface states [2]. Time permitting, I will conclude with some ongoing work on  CeNiSn, where evidence suggests that this material is on the brink of a topological phase transition involving non-Abelian crystalline symmetries. I will discuss the new topological classification and its fascinating Mobius twisted surface states.

[1] V. Alexandrov, P. Coleman, O. Erten Phys. Rev. Lett. 114, 177202 (2015).
[2] O. Erten, P. Ghaemi, P. Coleman Phys. Rev. Lett. in press; arXiv: 1510.02313 (2015).

Work supported by Department of Energy grant DE-FG02- 99ER45790