Excitonic and nematic instabilities on the surface of topological Kondo insulators
Abstract
We study the effects of strong electronelectron interactions on the surface of cubic topological Kondo insulators (such as samarium hexaboride, SmB_{6}). Cubic topological Kondo insulators generally support three copies of massless Dirac nodes on the surface, but only two of them are energetically degenerate and exhibit an energy offset relative to the third one. With a tunable chemical potential, when the surface states host electron and hole pockets of comparable size, strong interactions may drive this system into rotational symmetry breaking nematic and translational symmetric breaking excitonic spin or chargedensitywave phases, depending on the relative chirality of the Dirac cones. Taking a realistic surface band structure into account we analyze the associated GinzburgLandau theory and compute the meanfield phase diagram for interacting surface states. Beyond meanfield theory, this system can be described by a twocomponent isotropic AshkinTeller model at finite temperature, and we outline the phase diagram of this model. Our theory provides a possible explanation of recent measurements which detect a twofold symmetric magnetoresistance and an upturn in surface resistivity with tunable gate voltage in SmB_{6}. Our discussion can also be germane to other cubic topological insulators, such as ytterbium hexaboride (YbB_{6}) and plutonium hexaboride (PuB_{6}).
 Publication:

Physical Review B
 Pub Date:
 December 2015
 DOI:
 10.1103/PhysRevB.92.245431
 arXiv:
 arXiv:1410.1868
 Bibcode:
 2015PhRvB..92x5431R
 Keywords:

 73.20.r;
 71.35.Lk;
 Electron states at surfaces and interfaces;
 Collective effects;
 Condensed Matter  Mesoscale and Nanoscale Physics
 EPrint:
 9+epsilon pages, 3 figures: Published version, added discussion and new references