Abstract
The doping and temperature dependence of the complex conductivity is determined for the ferromagnetic semiconductor . A broad resonance develops with Mn doping at an energy scale of , well within the GaAs band gap. Possible origins of this feature are explored in the context of a Mn induced impurity band and intervalence band transitions. From a sum rule analysis of the conductivity data the effective mass of the itinerant charge carriers is found to be at least a factor of 3 greater than what is expected for hole doped GaAs. In the ferromagnetic state a significant decrease in the effective mass is observed, demonstrating the role played by the heavy carriers in inducing ferromagnetism in this system.
- Received 15 May 2002
DOI:https://doi.org/10.1103/PhysRevLett.89.097203
©2002 American Physical Society