Frustrating Quadrupolar Interaction and Possible Pressure Effects in PrOs_4Sb_<12>(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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The skutterudite superconductor PrOs_4Sb_<12> exhibits a field-induced phase transition that is interpreted as an antiferro-quadrupolar (AFQ) ordering in the low-lying singlet-triplet crystal field levels. In this paper, we investigate the properties of the possible AFQ state in lower magnetic fields which can be realized with hydrostatic and uniaxial pressures. Making use of a new pseudo-spin description, we show that the AFQ model at zero field is well approximated as the quantum four-state Potts model with macroscopic ground-state degeneracy. Some consequences of this mapping and the resulting magnetic field effects on the AFQ state are discussed. In particular, it is shown that a type of uniaxial strains can stabilize the AFQ state in low fields by relaxing the frustration in the Potts limit. Based upon such findings, we study the mean field solutions of the original AFQ model as a function of the magnetic field. The evolutions from the field-induced order to the zero-field one are elucidated by changing the crystal field and the uniaxial strains. The origin of a marked anisotropy for the strain direction is discussed in relation with the competing nature of the AFQ interaction.
社団法人日本物理学会の論文
2006-11-15