Cyclotron decay time of a two-dimensional electron gas from 0.4 to 100 K

Abstract

We have studied the cyclotron decay time of a Landau-quantized two-dimensional electron gas as a function of temperature (0.4--100 K) at a fixed magnetic field ($\ifmmode\pm\else\textpm\fi{}1.25\phantom{\rule{0.16em}{0ex}}\mathrm{T}$) using terahertz time-domain spectroscopy in a gallium arsenide quantum well with a mobility of ${\ensuremath{\mu}}_{dc}=3.6\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ and a carrier concentration of ${n}_{s}=2\ifmmode\times\else\texttimes\fi{}{10}^{11}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$. We find a cyclotron decay time that is limited by superradiant decay of the cyclotron ensemble and a temperature dependence that may result from both dissipative processes as well as a decrease in ${n}_{s}$ below $1.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Shubnikov--de Haas characterization determines a quantum lifetime, ${\ensuremath{\tau}}_{q}=1.1\phantom{\rule{0.16em}{0ex}}\mathrm{ps}$, which is significantly faster than the corresponding dephasing time, ${\ensuremath{\tau}}_{s}=66.4\phantom{\rule{0.16em}{0ex}}\mathrm{ps}$, in our cyclotron data. This is consistent with small-angle scattering as the dominant contribution in this sample, where scattering angles below $\ensuremath{\theta}\ensuremath{\le}{13}^{\ensuremath{\circ}}$ do not efficiently contribute to dephasing. Above $50\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the cyclotron oscillations show a strong reduction in both the oscillation amplitude and lifetime that result from polar optical phonon scattering.