Coexistence of odd-parity and even-parity order parameters in the multipole order phase of the spin-orbit coupled metal Cd2Re2O7

摘要

Magnetic torque measurements have been performed to investigate the phase transitions of the metallic pyrochlore compound Cd2Re2O7, in which a spin-orbit (SO) interaction leads to unique multipole orders associated with an inversion symmetry breaking. We find that the magnetic torque signals with a fourfold symmetry (tau(4) proportional to H-4) as well as a twofold symmetry (tau(2) proportional to H-2) are significantly enhanced at low temperatures below a structural phase transition temperature (similar to 200 K). The analyses of the torque curve symmetries show that the tau(4) term arises from an even-parity order parameter (OP) with the irreducible representation E-g, whereas the tau(2) term from an odd-parity OP with E-u, T-1u, or T-2u. The parity mixing of the primary OPs shows a peculiar phase transition in the SO coupled Cd2Re2O7. The coexistence of the two OPs provides important insights into the origin of the multipole orders induced by the SO interaction.