ANGULAR DEPENDENT MAGNETORESISTANCE OSCILLATION OF A QUASI-2-DIMENSIONAL SYSTEM IN A PERIODIC POTENTIAL

(BEDT-TTF)(2)MHg(SCN)(4)[M: K, Rb, TI] shows typical two-dimensional angular dependent magnetoresistance oscillation (ADMRO) at high temperatures (T> 8 K), but at lower temperatures it shows anomalously large magnetoresistance, and the ADMRO pattern changes. These low-temperature behaviors are explained as effects of a periodic potential. The present explanation is different from that by Kartsovnik et al. [J. Phys. I 3 (1993) 1187] in that reconstruction of the cylindrical Fermi surface into an open Fermi surface is not assumed. It is also predicted that if the periodic potential exists at quantizing magnetic field, where only a few Landau subbands cross the Ferni level, a resistivity peak of new origin should be observed.