Logarithmic AC Response in Rb_3C_<60> Crystals

概要

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AC susceptibility measurements were performed on Rb_3C_<60> crystals. Two peaks are observed in the imaginary part of the susceptibility X"(T) and the peak near the transition temperature T_c is more pronounced. This is interpreted in terms of weak links in the fullerene superconductors. The temperature associated with the intragranular X" maximum T_m exhibits extremely weak dependence on ac frequency f; T_m shifts to higher temperature with increasing f and the effect is enhanced by increasing dc magnetic-field amplitude H_<dc> or ac amplitude h_<ac>. The inverse temperature 1/T_m is found to depend roughly linearly on logarithmic frequency. This result is consistent with the prediction of the thermally activated flux creep model. This implies that the ac power dissipation in the Rb_3C_<60> superconductors is predominantly due to hysteretic losses and therefore that magnetic flux is in the irreversible regime of the magnetic phase diagram. The thermal activation energy for flux lines U_0 is estimated to be ≈ 6.1 eV at H_<dc>=1 kOe and h_<ac>=l Oe. Finally, (l-T_m/T_c)^<3/2> is found to depend linearly on In f.
社団法人応用物理学会の論文
1996-06-15