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Abstract:
The specific heat C(T) of Bi2Sr2CaCu2O8 was measured at 80 mK ≤ T ≤ 40 K and in magnetic fields up to 8 T. For T ≤ 400 mK, C(T) is well described by C(T) = γ* centerdot T + α/T2. For increasing temperature as well as for increasing magnetic field, the coefficient γ* of the linear term is strongly depressed. This result is interpreted best in terms of spin-glass physics due to a very low (≈ 0.1%) concentration of localized Cu2+ moments, consistent with the absence of any sizeable Curie term in the normal-state magnetic susceptibility.
