Pressure effects on the CDW transitions and magnetoresistances in NbSe₃

Abstract
Magnetoresistance (MR) of NbSe₃ has been measured between 2 K alid 150 K under high pressure including critical pressures (P_c2 and P_c1) where the lower and upper CDW phase are totally suppressed by pressure respectively. At ambient pressure, a large MR (LMR) is observed just below T_c2 but no MR is detected above T_c2. Under high pressure, in addition to the LMR, we observe newly a MR above T_c2. Here we call il the pressure-induced MR (PIMR). The LMR always appears as long as the lower CDW phase exists but it rapidly disappears above P_c2. Similarly, the PIMR disappears above P_c1. Furthermore, no anomalies associated with the field-induced CDW are observed within our experimental limits. From these findings, we claim that the LMR and PIMR are due to normal carriers in small pockets created by a pressure-dependent imperfect nesting of the Fermi surface in the CDW transitions.