Interplay between Angular-Dependent Magnetoresistance Oscillation and Charge-Ordered States in the Organic Conductor β"-(ET)(TCNQ)

In this paper, we report on the effect of pressure on the angular-dependent magnetoresistance and Shubnikov-de Haas (SdH) oscillation for beta"-(ET)(TCNQ), where ET and TCNQ stand for bis(ethylenedithio)tetrathiafulvalene and tetracyanoquinodimethane, respectively. At 0 kbar, the temperature dependence of the interlayer resistance shows three hump anomalies at around T-1 = 174 K, T-2 = 72 K, and T-3 = 22 K. At low temperatures below T-3, both the Yamaji oscillation and the periodic dip structure due to a commensurability effect are clearly observed in the angular dependence of the interlayer resistance at high magnetic fields. At 2.0 kbar, the T-1-anomaly is suppressed and the T-2- and T-3-anomalies shift to lower temperatures. Below T-3, a similar Yamaji oscillation and the dip structure are evident. At 5.1 kbar, the T-3-anomaly is removed, and only the dip structure is clearly observed at low temperatures. From this finding, the dip structure is attributable to a commensurability effect between the possible 4kF charge-density wave in the TCNQ layers and the interlayer lattice potential. Although no Yamaji oscillation is observed at 5.1 kbar, a higher SdH frequency than that at 0 kbar is detected, suggesting the emergence of a magnetic breakdown orbit in the significantly undulated Fermi surface originating from the ET layers. The temperature-pressure phase diagram of beta"-(ET)(TCNQ) is determined from the resistance measurements.