Electrical resistivity and thermoelectric power of a quasi-one-dimensional Nb₃Te₄ single crystal inserted with mercury: Hg_xNb₃Te₄

The electrical resistivity and the thermoelectric power of Nb₃Te₄ inserted with mercury have been measured in the temperature range from 1.4 to 300 K. The magnitude of the resistivity and the residual-resistivity ratio are not greatly affected by addition of Hg. The magnitude of the resistive anomaly at 90 K increases when adding a small amount of Hg but begins to decrease at about x = 0.03 and is no longer visible at about x = 0.15. Similarly, the magnitude of the resistive anomaly at 30 K decreases with increasing Hg concentration and disappears at about x = 0.26. The thermoelectric power S also shows two anomalies at about 90 and 30 K. The anomaly of S at 90 K becomes smeared by addition of Hg and disappears at about x = 0.3. The anomaly of S at 30 K becomes clear by addition of Hg and is still present at an amount of x = 0.8. The sign of S is negative at all measured temperatures for x<0.3 and is positive at temperatures below 7 K for x>0.3. The superconducting transition temperature is enhanced from 1.9 to 5.4 K by addition of Hg. The upper critical fields parallel (H_c2∥) and perpendicular (H_c2⊥) to the c axis have been measured near T_C. The critical fields show large anisotropy for x≥0.3: the ratio H_c2∥/H_c2⊥ is about 5 for x<0.3 and 40 for x≥0.3. These results are discussed on the basis of the multiband model with electron-like and hole-like carriers and with phonon drag.