Hidden-order symmetry and superconductivity in URu_2Si_2 investigated by quasiparticle interference

摘要

The hidden order (HO) in URu_2Si_2 has been determined as a high-rank multipole formed by itinerant 5f electrons with distinct orbital structure imposed by the crystalline electric field. Because this can lead to a considerable number of different multipoles, it is of great importance to use microscopic techniques that are sensitive to their subtle physical differences. Here, we investigate whether the quasiparticle interference (QPI) method can distinguish between the two most frequently proposed HO parameter models: the even rank-4 hexadecapole and the odd-rank-5 dotriacontapole model. We obtain the quasiparticle dispersion and reconstructed Fermi surface in each HO phase adapting an effective two-orbital model of 5 f bands that reproduces the main Fermi surface sheets of the para phase. We show that the resulting QPI spectrum reflects directly the effect of fourfold symmetry breaking in the rank-5 model, which is absent in the rank-4 model. Therefore we suggest that the QPI method should give the possibility of a direct discrimination between the two most investigated models of HO in URu_2Si_2. Furthermore, the signature of proposed chiral d-wave superconducting (SC) order parameter in QPI of the coexisting HO + SC phase is investigated.