Electronic Conduction in the Commensurate Charge Density Wave State of 1T-TaS₂

Abstract

We measured the Hall coefficient and the resistivity of 1T-TaS₂ prepared under various growth conditions. We observed a steep decrease of the Hall coefficient above about 130 K in every sample. From this result, also from the unexpectedly low carrier density estimated from the value of the Hall coefficient, we conclude that other gapping mechanism than the CDW formation is working at T_d′∼200 K, such as the Mott localization which Fazekas and Tosatti suggested. As the result 1T-TaS₂ becomes a kind of dirty semiconductor in the CCDW state. By introducing a gap in the spectrum we successfully analyzed the electronic conduction in high T region above 130 K, by a simple two-carrier model involving holes and thermally activated electrons across a gap.