Influence of infrared illumination on precision measurements of the integer quantum Hall effect

The preliminary result reported here unambiguously shows that infrared illumination of a nonfully quantized QHE sample can restore its ideal behaviour. Differences as large as 0.1 ppm in the Hall resistance have disappeared when the sample is illuminated by 150 ms pulses of infrared light. In parallel, the contact resistances of nonideal terminals have been found to decrease with the illumination time, although some high resistance contacts did not show any dependence on illumination. In addition, the illumination leads to an increase of the critical current, although the way this increase is taking place seems to be nonuniversal.