Signature of surface state coupling in thin films of the topological Kondo insulatorSmB6from anisotropic magnetoresistance

The temperature and thickness dependencies of the in-plane anisotropic magnetoresistance (AMR) of ${\mathrm{SmB}}₆$ thin films are reported. We find that the AMR changes sign from negative (${\ensuremath{\rho}}_||<{\ensuremath{\rho}}_{\ensuremath{\perp}}$) at high temperatures to positive (${\ensuremath{\rho}}_||>{\ensuremath{\rho}}_{\ensuremath{\perp}}$) at low temperatures. The temperature, ${T}_s$, at which this sign change occurs, decreases with increasing film thickness $t$ and ${T}_s$ vanishes for $t\phantom{\rule{4pt}{0ex}}>$ 30 nm. We interpret our results in the framework of a competition between two components: a negative bulk contribution and a positive surface AMR.