RKKY Interactions and Multipole Order in Ab initio Wannier Model of CeCoSi

Abstract

We calculate the RKKY interactions derived from ab initio calculations for the intermetallic compound CeCoSi exhibiting the hidden nonmagnetic order at T₀ and examine the instability towards possible multipole orders within the random phase approximation. All 36 multipole interactions up to rank 5 are investigated, and the maximum susceptibility exhibits an antiferro order with q = 0 for nonmagnetic multipoles of monopole I and hexadecapole H₀, yielding a charge imbalance of f electrons at two Ce atoms in the unit cell. The obtained order can explain some experiments.