Metallic Behavior of Cyclotron Relaxation Time in Two-Dimensional   Systems
  Cyclotron resonance of two-dimensional electrons is studied at low temperatures down to 0.4 K for a high-mobility Si/SiGe quantum well which exhibits a metallic temperature dependence of dc resistivity $\rho$. The relaxation time $\tau_{\rm CR}$ shows a negative temperature dependence, which is similar to that of the transport scattering time $\tau_t$ obtained from $\rho$. The ratio $\tau_{\rm CR}/\tau_t$ at 0.4 K increases as the electron density $N_s$ decreases, and exceeds unity when $N_s$ approaches the critical density for the metal-insulator transition. 
Ryuichi Masutomi, Kohei Sasaki, Ippei Yasuda, Akihito Sekine, Kentarou   Sawano, Yasuhiro Shiraki, Tohru Okamoto
cond-mat.mes-hall