  Highly disordered superconductors, in the magnetic-field-driven insulating
state, can show discontinuous current-voltage characteristics. Electron
overheating has been shown to give a consistent description of this behavior,
but there are other, more exotic, explanations including a novel,
superinsulating state and a many-body localized state. We present AC-DC
crossed-measurements, in which the application of a DC voltage is applied along
our sample, while a small AC voltage is applied in the transverse direction. We
varied the DC voltage and observed a simultaneous discontinuity in both AC and
DC currents. We show that the inferred electron-temperature in the transverse
measurement matches that in the longitudinal one, strongly supporting electron
overheating as the source of observed current-voltage characteristics. Our
measurement technique may be applicable as a method of probing electron
overheating in many other physical systems, which show discontinuous or
non-linear current-voltage characteristics.
