A new method is described for observing cyclotron resonance in photoconductors such as the alkali halides, where it is difficult to generate a high density of free carriers. The method consists of observing the changes in transient photocurrents brought about by switching on a microwave (70-Gc/sec) electric field in a plane to which static magnetic and electric fields are perpendicular. The maximum effect occurs at cyclotron resonance and is due to an electron heating phenomenon. By means of this technique the mass of the electron polaron in KBr is found to be $m^{*}=(1.1\mathrm{}\pm 0.15)m_e$. On the basis of the Feynman polaron model, this corresponds to a band mass of $m=0.48\mathrm{}{m}_e$ and a coupling constant of $\alpha =3.7\mathrm{}$.

• Received 15 March 1967

DOI:https://doi.org/10.1103/PhysRev.162.848