Field-induced CDW phases in a quasi-one-dimensional organic conductor, HMTSF-TCNQ under pressure of 1 GPa in magnetic field of 31 T

HMTSF-TCNQ is a quasi-one-dimensional organic conductor which undergoes CDW(charge density wave) transition at 30 K at ambient pressure, where HMTSF-TCNQ is hexamethylenetetraselena fulvalene-tetracyano quino dimethane. This CDW is suppressed by the pressure of 1 GPa. At this pressure, we found field-induced successive hysteretic transitions in magnetoresistance. This reminds us of the successive field-induced SDW (spin density wave) phases in TMTSF₂X salts. However, the field range of interest is 2-3 times higher than that of TMTSF₂X salts. Therefore, we need really high field to examine these properties. It is very likely that the field induced phases are of field induced CDW (FICDW), where quantum Hall effect and many interesting phenomena are expected like in the case of FISDW. Together with the magnetoresistance study up to the field of 31 Tesla and at temperatures down to 0.4 K in various magnetic field angles respective to the crystal axes, we examined the angular dependence of magnetoresistance oscillations(AMRO). It turned out that AMRO demonstrates clearly the occurrence of field-induced phase rather than the magneto-resistance by field sweep. Since the Hall resistance, R _xy in the field-induced phases showed stepwise plateau structure against the field sweep, and its strength was in the order of magnitude of h/e ² per molecular sheet, the Hall effect is very suggestive of quantum Hall effect.