Pressure-Induced Metal-Insulator Transition in Single-Walled Carbon Nanotubes

The resistance of single-walled carbon nanotube (SWNT) bundles was studied under combined extreme conditions of high pressure (up to 10 GPa), low temperature (down to 2 K) and strong magnetic field (up to 12 T). A pressure-induced metal-insulator transition was found to occur at $\sim $ 1.5 GPa, across which the temperature and field-dependent functional forms of the resistance changes dramatically. The transition pressure of $\sim $ 1.5 GPa correlates closely with the structural phase transition of SWNT under pressure. In the insulator phase, the magnetoresistance of the samples shows typical behaviors of two-dimensional electron weak localization, presumably reflecting the coherent hopping processes of the electrons in the collectively flattened plane of the SWNTs bundles.