ELECTRICAL-RESISTIVITY OF SINGLE-CRYSTAL GRAPHITE UNDER PRESSURE - ANANISOTROPIC 3-DIMENSIONAL SEMIMETAL

The in-plane (rho(a)) and c-axis (rho(c)) resistivities of natural sin gle-crystal graphite have been measured from 4 to 450 K at zero pressu re and from 77 to 450 K under pressures up to 500 MPa. Data for rho(c) differ strongly from earlier results obtained on synthetic graphite i n showing a strong T dependence of the pressure coefficient, while dat a for rho(a) agree well with those from previous studies. Our results can be analyzed quantitatively in a simple free-electron model, and we conclude that in contrast to quasi-two-dimensional synthetic graphite ,natural single-crystal graphite is an anisotropic three-dimensional s emimetal.