Superconductivity in a New Pseudo-Binary Li_2B(Pd_<1-x>Pt_x)_3 (x=0-1) Boride System(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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Recently we have found superconductivity in a cubic antiperovskite-like compound Li_2BPd_3. A new pseudo-binary complete solid solution Li_2B(Pd_<1-x>Pt_x)_3, x=0-1 with similar structure has been synthesized and observation of superconductivity in the entire x-range is reported. Our results strongly suggest that superconductivity is of bulk type. Critical temperature T_c is decreasing approximately linearly with amount (x) of Pt from 7.2-8K for Li_2BPd_3 to 2.2-2.8K for Li_2BPt_3. From isothermal magnetization (M-H) measurements, lower critical fields H_<cl> (138 Oe/_<x=0>, 38Oe/_<x=1>), upper critical fields H^<WHH>_<c2> (3.4T/_<x=0>, 1T/_<x=1>), coherence length ξ(0) (9.8nm/_<x=0>, 17.9nm/_<x=1>) and penetration depth λ(0)(190nm/_<x=0>, 364nm_<x=1>) were estimated and shown to follow approximately linear dependencies with x, either. Structure and superconducting similarities with MgCNi_3, viewed as a bridge between low and high T_c superconductors are increasing the expectations that Li_2B(Pd_<1-x>Pt_x)_3, x=0-1 superconductor can be included in the same class of'intermediate'superconductors. For x=0-1 a weak fishtail effect was observed at low and intermediate fields. Apart from this effect, some samples for x=1 have shown magnetization jumps at fields close to H_<c2>.
社団法人日本物理学会の論文
2005-03-15