The hall effect in HMTSeF-TCNQ

Abstract

The Hall effect in the organic charge transfer compound HMTSeF-TCNQ was measured as function of temperature and pressure. The Hall constant indicates metallic behaviour near ambient temperature, and semi-metallic behaviour at low temperatures, with approximately one carrier per 500-1000 formula units. The Hall constant changes sign around 32-36 K from hole-like at high temperatures to electron-like at low ones. The magnetoresistance was also measured as function of temperature and pressure, and found to be very large and anisotropic. The anisotropy in the resistivity was also measured as function of temperature and pressure, and the resistance in the crystalline direction of the Se—N bonds rises very rapidly below 20 K, much faster than the resistivity along the stacking axis. The carrier mobility under pressure at low temperature rises to approximately 4 x 104 cm2/Vs. Thus the semi-metallic nature of this material at low temperatures, under pressure, has been established and the Hall constant investigated for the first time in an organic metal