Generalized model of the noise spectrum of a two-level fluctuator in the presence of an electron subbath

The work of Ahn et al. [S. Ahn, S. Das Sarma, and J. P. Kestner, Phys. Rev. B 103, L041304 (2021)] derives the noise power spectrum of a two-level fluctuator (TLF) in the case where it interacts only with a subregion of a full electron bath and thus is subject to a fluctuating temperature. However, Eq. (1), which gives the variance of the subbath temperature in terms of the heat capacity, in that work carries the implicit assumption that the heat capacity of this subbath may be taken to be a constant, which is a good approximation at higher temperatures, but breaks down at lower temperatures. We thus extend this work to the case in which the fact that the electronic heat capacity of a two-dimensional electron gas (2DEG) CV∝T₀, where T₀ is the temperature of the full 2DEG, rather than constant in temperature, is fully taken into account. We show that, at low temperatures, the resulting power spectrum of the noise S(ω,T₀)∝e^-C/T₀3/8, in contrast to S(ω,T₀)∝e^-C^'/T₀1/3 as found previously, where C and C^' are constants. We also compare the numerical results that one would obtain from the two models and find that our results for S(ω,T₀) can differ from those of Ahn et al. by several orders of magnitude at low temperatures. Finally, we perform a fit of the spectra of two TLFs to experimental data from Connors et al. [E. J. Connors, J. J. Nelson, H. Qiao, L. F. Edge, and J. M. Nichol, Phys. Rev. B 100, 165305 (2019)] using our results and find excellent agreement with the data over most of the temperature range considered in the experiment.