Abstract
All symmetry-allowed couplings between the -electron ground state doublet of trivalent praseodymium in and and displacements of the phosphorus, iron, or ruthenium ions are considered. Two types of displacements can change the crystal lattice from body-centred cubic to simple orthorhombic or to simple cubic. The first type lowers the point group symmetry from tetrahedral to orthorhombic, while the second type leaves it unchanged, with corresponding space group reductions and , respectively. In former case, the lower point group symmetry splits the degeneracy of the doublet into states with opposite quadrupole moment, which then leads to antiquadrupolar ordering, as in . Either kind of displacement may conspire with nesting of the Fermi surface to cause the metal-insulator or partial metal-insulator transition observed in and . We investigate this scenario using band-structure calculations, and it is found that displacements of the phosphorus ions in (with space-group reduction ) open a gap everywhere on the Fermi surface.
- Received 16 March 2004
DOI:https://doi.org/10.1103/PhysRevB.70.245112
©2004 American Physical Society