THERMOPOWER BEHAVIOR OF INCOMMENSURATE CHARGE-DENSITY WAVE SYSTEMS (NBSE4)10/3I AND (TASE4)2I

The temperature dependence of thermoelectric power has been measured in the quasi-one dimensional charge density-wave (CDW) systems (NbSe4) 10 3 I and (TaSe4)2 I. In the (NbSe4) 10 3 I system, the thermopower remains positive throughout the temperature range investigated (120-350 K) whereas for (TaSe4)2 I it changes sign from negative values above the Peierls transition temperature (Tp = 263 K to positive values below Tp. Both these results are in agreement with Hall effect measurements. In addition we deduce from the temperature dependence of thermopower below Tp that there exists larger electron-hole asymmetry (σe/σh) in (NbSe4) 10 3 I as compared to (TaSe4)2 I. The unusual behaviour of thermopower below a temperature (Tm) in these and other incommensurate systems is attributed to CDW drag effects of Umklapp type. © 1990.