Influence of collective effects on the linewidth of intersubband resonance

We have measured the intersubband resonances of an InAs/AlSb quantum well with two occupied subbands from cryogenic temperatures to well above room temperature. The higher energy mode is very robust with increasing temperature; the lower energy mode, however, broadens above 200 K. We explain the results in terms of Landau damping and argue generally that the collective nature of the intersubband resonance is crucial for an understanding of the scattering mechanisms that determine the intersubband resonance linewidth.