Magnetoresistance evidence of a surface state and a field-dependent insulating state in the Kondo insulator SmB6

Recently the resistance saturation at low temperature in the Kondo insulator SmB6, a long-standing puzzle in condensed matter physics, was proposed to originate from a topological surface state. Here we systematically studied the magnetoresistance of SmB6 at low temperature up to 55 T. For temperature decreasing below 16 K, the temperature-dependent magnetoresistance exhibits a negative magnetoresistance, while the angular-dependent magnetoresistance shows a fourfold symmetry. Below 5 K, both temperature-and angular-dependent magnetoresistances show a similar crossover behavior in which the negative magnetoresistance is strongly suppressed and a twofold angular-dependent magnetoresistance appears. Furthermore, the angular-dependent magnetoresistance on a different crystal face confirms a two-dimensional surface state as the origin of magnetoresistance crossover below 5 K. Based on a two-channels model consisting of both surface and bulk states, the critical magnetic field (H-c) of 125 T for field-dependent insulating behavior is extracted from our temperature-dependent resistance under different magnetic fields. Our results have important implications in understanding the novel low-temperature transport behavior in SmB6.