Quantum fluctuations of Coulomb potential as a source of Flicker noise: the influence of a heat bath

The power spectrum of finite-temperature quantum electromagnetic fluctuations produced by elementary charge carriers under the influence of an external electric field is investigated. It is found that under the combined action of the photon heat bath and the external field, the low-frequency asymptotic of the power spectrum is modified both qualitatively and quantitatively. The new term in the power spectrum is inversely proportional to frequency, but is odd with respect to it. It comes from the connected part of the correlation function, and is related to the temperature and external field corrections to the photon and charge carrier propagators. In application to the case of a biased conducting sample, this term gives rise to a contribution to the voltage power spectrum which is proportional to the absolute system temperature, the charge carrier mobility, the bias voltage squared, and a factor describing dependence of the noise intensity on the sample geometry. It is verified that the derived expression is in agreement with the experimental data on 1 / f -noise measurements in metal films. It is shown also that the obtained result provides a natural resolution to the problem of divergence of the total noise power.