Submillimeter wave ESR and cyclotron resonance measurements of α-(BEDT-TTF)2NH4Hg(SCN)4

Both ESR and cyclotron resonance of α-(BEDT-TTF)2NH4Hg(SCN)4 have been observed simultaneously at 1.8K using our new high resolution detecting system. The observed frequency region is from 50 to 383 GHz, and the pulsed magnetic field up to 15 T is applied perpendicular to the ac-plane. Very sharp resonance at g=2 is attributed to ESR, while broad resonance is attributed to CR whose effective mass is determined to be 0.96 me by our frequency dependence measurement, where me is the free electron mass. These results will be discussed with the previous measurements on NH4 salt and with the results of other α-BEDT-TTF salts.