The effect of high pressures on the quantum limit of graphite

Graphite is a semi-metal with a low carrier density that can be tuned to the quantum limit with a comparatively small magnetic field of ~ 7.5 T. Below this quantum limit, a magnetic field applied perpendicular to the layers exhibits Shubnikov-de Haas oscillations of two different frequencies, corresponding to the hole and electron fermi surfaces, each of which has a different effective mass. Previous measurements suggest that the carrier imbalance remains constant up to 25 T, above which multiple field induced phase transitions are observed. While much attention in recent years has focused on these high field states, we seek to better understand how the low temperature, low field ground state of the material is altered with the application of pressure and determine what effect if any that has on the carrier imbalance and the quantum limit. We will discuss the results of these studies in fields below 15 T and to pressures in excess of 20 kbar.