Quadrupolar Order, Hidden Octupolar Order and Tiny Magnetic Moment in URu_2Si_2 : Condensed Matter: Electronic Properties, etc.

概要

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Possible orders in URu_2Si_2 are investigated using a two-channel degenerate Anderson model. The ground state of uranium ions is the non-Kramers quadrupolar doublet Γ_5 with (5f)^2, and its relevalent excited state is the Kramers dipolar doublet Γ_7 with (5f)^1 . These states mix with each other via conduction electrons. At low temperatures, the system forms renormalized bands with both quadrupole and dipole degrees of freedom due to the quadrupolar Kondo effect which slightly mixes quadrupolar Γ_5, a primary state of uranium ions, with dipolar Γ_7. At a certain low temperature, conduction electrons in the renormalized bands undergo quadrupolar ordering with a large quadrupolar moment. At a further lower temperature, octupolar ordering occurs, accompanied by a tiny dipolar moment which is attributed to the property of the renormalized bands with primarily the Γ_5-character slightly mixed with the Γ_7-character. These phenomena are well described by the 1/N-expansion method with pseudo-fermions for the non-Kramers doublet _5 and slave bosons for the Kramers doublet _7.
社団法人日本物理学会の論文
2000-03-15