Pressure dependence of the resistivity of single-wall carbon nanotube ropes

We have performed dc transport measurements on purified thick films of single-walled carbon nanotubes under hydrostatic pressures up to 2 GPa in the temperature range 4–300 K. At room temperature we have found nonmonotonic variation of the resistance with applied pressure. The resistance first drops with increasing pressure, but in the range where hexagonal deformation of the tubes is evidenced by the Raman experiments of Venkateswaran et al. [Phys. Rev. B 59, 10 928 (1999)], we see a fast increase in sample resistivity acompanied by very long time-scale relaxations. The temperature dependence of the resistivity does not change much with pressure, and we find an $\exp \left[{(T}_0{/T)}^{1/4}\right]$ temperature dependence indicating hoppinglike conduction.