Radio frequency tunable oscillators are vital electronic components for signal generation,
characterization, and processing. They are often constructed with a resonant circuit
and a 'negative' resistor, such as a Gunn-diode, involving complex structure and large
footprints. Here we report that a piece of SmB6, 100 micron in size, works as a current-controlled
oscillator in the 30 MHz frequency range. SmB6 is a strongly correlated Kondo insulator
that was recently found to have a robust surface state likely to be protected by the
topology of its electronics structure. We exploit its non-linear dynamics, and demonstrate
large AC voltage outputs with frequencies from 20 Hz to 30 MHz by adjusting a small
DC bias current. The behaviors of these oscillators agree well with a theoretical
model describing the thermal and electronic dynamics of coupled surface and bulk states.
With reduced crystal size we anticipate the device to work at higher frequencies,
even in the THz regime. This type of oscillator might be realized in other materials
with a metallic surface and a semiconducting bulk.