Cyclotron resonance of α-(BEDT-TTF)2RbHg(SCN)4 observed at above and below the transition temperature

Cyclotron resonances of α-(BEDT-TTF)2RbHg(SCN)4 have been measured for the first time in the frequency region from 50 GHz to 383 GHz at temperature from 1.8 K to 50 K using the pulsed magnetic field up to 15 T. Three resonances, whose effective masses correspond to 0.53me, 0.77me and 0.97me, have been observed at 1.8 K. Although the crystal structure of this Rb salt is very similar to that of K salt, this result is in contrast with the observation of four resonances in the case of α-(BEDT-TTF)2KHg(SCN)4. The temperature dependence measurement of the Rb salt showed the disappearance of two resonances and the resonance corresponding to the effective mass of 0.97me remained above the density wave transition temperature at 10 K.