  SmB6 is a mixed valence Kondo insulator that exhibits a sharp increase in
resistance following an activated behavior that levels off and saturates below
4K. This behavior can be explained by the proposal of SmB6 representing a new
state of matter, a Topological Kondo insulator, in which a Kondo gap is
developed and topologically protected surface conduction dominates
low-temperature transport. Exploiting its non-linear dynamics, a tunable SmB6
oscillator device was recently demonstrated, where a small DC current generates
large oscillating voltages at frequencies from a few Hz to hundreds of MHz.
This behavior was explained by a theoretical model describing the thermal and
electronic dynamics of coupled surface and bulk states. However, a crucial
aspect of this model, the predicted temperature oscillation in the surface
state, hasn't been experimentally observed to date. This is largely due to the
technical difficulty of detecting an oscillating temperature of the very thin
surface state. Here we report direct measurements of the time-dependent surface
state temperature in SmB6 with a RuO micro-thermometer. Our results agree
quantitatively with the theoretically simulated temperature waveform, and hence
support the validity of the oscillator model, which will provide accurate
theoretical guidance for developing future SmB6oscillators at higher
frequencies.
