Conductivity increase due to nonequilibrium conditions in an actual quasi-one-dimensional conductor with charge- or spin-density-wave gap

Abstract

We derive the gap equation for a uniform quasi-one-dimensional (1D) conductor with arbitrary band filling and use it to calculate the decrease in the gap of bis tetramethyl-tetraselenafulvalene hexafluorophosphate [${(\mathrm{TMTSF})}_{2}$P${\mathrm{F}}_{6}$] due to the presence of excess electron-hole pairs. An actual 1D conductor with a charge- or spin-density-wave gap should be nonuniform due to the presence of various types of defects. For a nonuniform conductor we predict a new effect in high electric fields: gap decrease due to injection across internal barriers between regions of different gap. This is expected to give rise to a characteristic instability. It could explain the very large increases in conductivity with field observed in materials such as tetrathiafulvalene tetracyanoquinodimethane (TTF-TCNQ) and ${(\mathrm{TMTSF})}_{2}$P${\mathrm{F}}_{6}$.