Signature of surface state coupling in thin films of the topological Kondo insulator SmB6 from anisotropic magnetoresistance

The temperature and thickness dependencies of the in-plane anisotropic magnetoresistance (AMR) of SmB6 thin films are reported. We find that the AMR changes sign from negative (ρ||<ρ¥) at high temperatures to positive (ρ||>ρ¥) at low temperatures. The temperature, Ts, at which this sign change occurs, decreases with increasing film thickness t and Ts vanishes for t> 30 nm. We interpret our results in the framework of a competition between two components: a negative bulk contribution and a positive surface AMR.