Linear Magnetoresistance in the Quantum Limit in Graphite

Abstract

Measurements of the galvanomagnetic properties of single-crystal graphite were made at 4.2°K in pulsed magnetic fields up to 160 kG. With the magnetic field parallel to the $c$ axis, the transverse magnetoresistance is approximately proportional to the magnetic field strength, and the Hall coefficient is constant above about 80 kG. The results imply that both the diagonal and off-diagonal elements of the magnetoconductivity tensor are inversely proportional to the magnetic field strength. The results are explained theoretically using the following facts: (1) both electrons and holes occupy their lowest Landau levels for fields stronger than about 60 kG, (2) degenerate statistics apply throughout the field range, and (3) the scattering is by ionized impurities whose range depends upon the magnetic field strength. The effect provides a simple way to determine the concentration of scattering centers in graphite. It is also definitely established that the concentration of excess carriers must be determined from the off-diagonal magnetoconductivity; use of the high-field Hall coefficient alone leads to large errors.