Direct Observation of Quadrupolar Excitons in the Heavy-Fermion SuperconductorPrOs4Sb12

Abstract

We report inelastic neutron scattering experiments performed to investigate the low energy magnetic excitations on single crystals of the heavy-fermion superconductor PrOs(4)Sb(12). The observed excitation clearly softens at a wave vector Q=(1,0,0), which is the same as the modulation vector of the field-induced antiferro-quadrupolar ordering, and its intensity at Q=(1,0,0) is smaller than that around the zone center. This result directly evidences that this excitonic behavior is derived mainly from nonmagnetic quadrupolar interactions. Furthermore, the narrowing of the linewidths of the excitations below the superconducting transition temperature indicates the close connection between the superconductivity and the excitons.

Muon spin rotation and relaxation inPr1−xNdxOs4Sb12: Paramagnetic states

“…The Knight-shift saturation sets in at temperatures in the neighborhood of the lowest Pr 3+ CEF excitation energy in PrOs 4 Sb 12 [33], suggesting that quadrupolar excitations observed at these energies [34] might be involved. Itinerant quadrupolar excitations (quadrupolar excitons) have been suggested as mechanisms for heavy-fermion behavior and Cooper-pair binding in superconducting PrOs 4 Sb 12 [35][36][37].…”

Suppression of Superconductivity in PrRh2Zn20by the Substitution of Co for Rh

“…An antiferroquadrupole (AFQ) order is induced by applying magnetic fields above 4 T [2]. Inelastic neutron scattering and nuclear quadrupole resonance experiments on PrOs 4 Sb 12 suggested possible role of quadrupole fluctuations in the superconducting pair formation [3,4].…”

Magnetic Field-Induced Anomalies and Kondo Effect in Lanthanide in Heavy-Electron Systems

“…As the divergence follows directly from the general analytic structure of the corresponding electron self energy it persists also in the self consistent solution for finite band width. 23) In concentrated systems the singlet-triplet excitations have a pronounced dispersion 62) and an applied field of critical strength therefore leads to a softening of ωq only in the restricted phase space around the AFQ ordering vector Q. Consequently the mass renormalization will be finite even at the critical field h c for AFQ order when ω Q =0.…”