Pressure effects to the anomalous state of quasi two-dimensional conductor alpha-(BEDT-TTF)(2)KHg(SCN)(4)

Quasi two-dimensional conductor alpha-(BEDT-TTF)(2)KHg(SCN)(4) has an anomalous electronic state in the low-temperature-low-magnetic-field-low-pressure regime below 8 K, 22 T, and 5 kbar. Angle dependent magnetoresistance oscillations in the anomalous state were measured under high pressure with the magnetic field rotated around two axes perpendicular to each other. We studied the topology of the Fermi surface below and above the critical pressure (5 kbar) to compare the normal state with the anomalous one. In the anomalous state, we found a new series of angle dependent magnetoresistance oscillations. In the normal state above the critical pressure, we found a quasi one-dimensional Fermi surface parallel to the b*c*-plane. This is considered to be responsible for the Fermi surface nesting that causes the anomalous state. Electronic states are discussed in relation to possible origins of the anomalous state.