Pressure dependence of the Fermi surface of Th

We report measurements of the pressure dependence of all three sheets of the Fermi surface of thorium. All of the cross-sectional areas investigated are found to decrease as the interatomic distance is diminished. This behavior is completely unprecedented for a cubic material and indicates that Th becomes less metallic with decreasing lattice spacing. We compare these results with calculations in which the unoccupied $5f$ electron bands are treated as itinerant and with a localized model ($5f$ states removed). While the itinerant model gives better normal-volume results as pointed out by Koelling and Freeman, the pressure results are only semiqualitatively reproduced by either model.