Ni-impurity effects on the superconducting gap of La2-xSrxCuO4 studied from the magnetic field and temperature dependence of the electronic specific heat

Article

关键词: DENSITY-OF-STATES;    D-WAVE SUPERCONDUCTORS;    CONDENSATION ENERGY;    PSEUDOGAP FORMATION;    TRANSITION;    SCALE;    NODES;   

DOI  :  10.1103/PhysRevB.85.134522

来源: SCIE

【 摘 要 】

The magnetic field and temperature dependence of the electronic specific heat C-el have been systematically investigated in La2-xSrxCu1-yNiyO4 (LSCNO) in order to study Ni-impurity effects on the superconducting (SC) gap. In LSCNO with x = 0.15 and y = 0.015, the value of gamma ( C-el/T) at T = 0 K, gamma(0), is enhanced under the magnetic field H applied along the c axis. The increment of gamma(0), Delta gamma(0), follows the Volovik relation Delta gamma(0) = A root H, characteristic of the SC gap with line nodes, with prefactor A similar to that of a pure sample. The C-el/T versus T curve under H = 0 shows a d-wave-like SC anomaly with an abrupt increase at T-c and T-linear dependence at T << T-c, although the gamma(0)-value in the C-el/T versus T curve increases with increasing Ni concentrations. Interestingly, as the SC part of C-el/T, C-el/T - gamma(0) gamma(s), decreases in LSCNO, T-c is reduced in proportion to the decrease of gamma(s). These findings can be explained phenomenologically by a simple model in which Ni impurities bring about strong pair breaking at the edges of the coherent nodal part of the Fermi surface but in the vicinity of the nodes of the SC gap. The reduction of the SC condensation energy U-0 in LSCNO, evaluated from C-el at T less than or similar to T-c, is also understood by the same model.

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