Defects states in bis-tetramethyltetraselenafulvalene hexafluorophosphate [(TMTSF)2PF6] and their effects on low-temperature transport

Abstract

Shallow electronic levels in the gap of bis-tetramethyltetraselenafulvalene hexafluorophosphate [${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$ P${\mathrm{F}}_6$], whether due to solitons or the hydrogenlike bound states typically found in three-dimensional semiconductors, should be very much more extended along the chain direction than transverse to it. The existence of such levels could explain otherwise puzzling low-temperature transport properties: (1) Hall constant positive for carriers moving parallel to the chains, while thermoelectric power along the chains is negative, and transverse to the chains positive, (2) increase in conductivity at microwave frequencies, and (3) the larger increase in conductivity with field observed at very low temperatures, ∼ 2 K.