Conductivity anisotropy and transverse magnetoresistance of NbSe3

The first-transverse de conductivity measurements on a member of the transiton-metal trichalcogenides (Nb${\mathrm{Se}}_3$) are presented. The conductivity anisotropy $\frac{{\sigma }_b}{{\sigma }_c}$ (where $b$ is the chain axis) was obtained using the Montgomery technique, and varies from 10 to 20 as a function of temperature. The transverse resistivity ${\rho }_c$ also shows anomalies associated with the charge-density-wave transitions at $T_1$ (142 K) and $T_2$ (58 K). However, these anomalies are smaller than the corresponding ones in ${\rho }_b$. The quantity $\frac{R_H\mathrm{}\left(0\right)\mathrm{}}{\left({\rho }_b{\rho }_c\right)}$, where $R_H$ is the Hall constant, demonstrates explicitly the freeze-out of thermally excited quasiparticles below each transition. We show that at both transition gaps appears on the hole surface, and the hole concentration decreases rapidly. The transverse magnetoresistance at low fields has also been measured. Its monotonic power-law decrease with increasing temperature shows explicitly that the resistivity anomalies are due to changes in the carrier concentration, and not in the lifetimes.