Cyclotron resonance of holes orbiting in the $a-b$ plane of an anthracene crystal has been observed. This represents the first time that this phenomenon has been observed in a molecular crystal. From these experiments, the hole effective mass is determined to be $11m_e$ where $m_e$ is the free-electron mass. The hole scattering time at 2°K was measured in two different crystals and found to be ∼7×${10}^{-11\mathrm{}}$ sec in one crystal and 4 ×${10}^{-10\mathrm{}}$ sec in the other.

• Received 29 July 1974

DOI:https://doi.org/10.1103/PhysRevLett.33.833