Magnetic quantum oscillations in the charge-density-wave state of the organic metals α-(BEDT-TTF)₂MHg(SCN)₄ with M = K and Tl

Abstract

The low-temperature charge-density-wave (CDW) state in the layered organic metals α-(BEDT-TTF)₂MHg(SCN)₄ has been studied by means of the Shubnikov–de Haas and de Haas–van Alphen effects. In addition to the dominant α-frequency, which is also observed in the normal state, both the magnetoresistance and magnetic torque possess a slowly oscillating component. These slow oscillations provide a firm evidence for the CDW-induced reconstruction of the original cylindrical Fermi surface. The α-oscillations of the interlayer magnetoresistance exhibit an anomalous phase inversion in the CDW state, whereas the de Haas–van Alphen signal maintains the normal phase. We argue that the anomaly may be attributed to the magnetic-breakdown origin of the α-oscillations in the CDW state. A theoretical model illustrating the possibility of a phase inversion in the oscillating interlayer conductivity in the presence of a spatially fluctuating magnetic breakdown gap is proposed.