Conductance-quantization broadening mechanisms in quantum point contacts

We have studied three types of broadening effects in quantum point contacts: temperature smearing, broadening due to high source-drain voltages, and broadening due to Joule heating. We are able to calculate the relative strength of the three mechanisms by using the parabolic-saddle-potential approximation. The voltage smearing effect can in most cases be disregarded in comparison with the thermal effects. The Joule heat produced in the constriction by the current is carried away by a thermal conductance intermediate between the low conductance of the quantum point contact and the high conductance of the surrounding two-dimensional electron gas, indicating which part of the dissipation results from the one-dimensional modes in the constriction.