MAGNETIZATION AS A PROBE OF THE PAIRING SYMMETRY IN BI2SR2CUO6+DELTA

We have measured the magnetisation in the mixed-state and the specific heat of Bi2.08Sr1.92CuO6+delta (Bi-2201). The wide reversible domain in the H-T plane allowed us to compare the data with existing predicti ons for different symmetries of the order parameter. We observed in th e limit of low temperatures: (a) a high ratio gamma/gamma(s) between the linear term of the specific heat gamma = C/T \(T-->0) and the Som merfeld constant gamma(s), (b) a quadratic variation in temperature of the inverse of the London penetration depth squared (Delta lambda(-2) = lambda(-2)(T) - lambda(-2)(0)alpha T-2), and (c) a logarithmic depe ndence of the second derivative of magnetisation (partial derivative(2 )M/partial derivative T-2 alpha 1nH). All these features are consisten t with new calculations, also reported in this paper, predicting the e ffects of non-magnetic impurities on d-wave superconductors. The isotr opic and anisotropic s-wave symmetries in the pure and impure limits a nd the d-wave symmetry in the pure limit seem to be ruled out. (C) 199 7 Elsevier Science B.V.