Novel Finite Temperature Conductivity in Quantum Hall Systems

We study quantum Hall systems (mainly the integer case) at finite temperatures and show that there is a novel temperature dependence even for a pure system, thanks to the `anomalous' nature of generators of translation. The deviation of Hall conductivity from its zero temperature value is controlled by a parameter $T_0 =\pi \rho /m^\ast N$ which is sample specific and hence the universality of quantization is lost at finite temperatures.