We demonstrate that the usual Kubo formula for thermal response functions is invalid if a magnetic field is present. There exists a fundamental correction due to a lack of time-reversal symmetry. We show in particular that, in addition to being of general importance in the theory of transport, this leads to a novel thermoelectric effect in a weakly disordered two-dimensional electron gas subject to a quantizing magnetic field. The thermopower tensor is calculated within the self-consistent Born approximation using a generalized Mott formula, which is derived.

• Received 20 October 1983

DOI:https://doi.org/10.1103/PhysRevB.29.1939