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Abstract |
The Y1-xPrxBa2Cu3O7-δ (δ ≈ 0.05) system has a rich temperature—praseodymium concentration (T-x) phase diagram consisting of a metal—insulator transition at xcr≈0.6, high Tc superconductivity in the metallic phase (0x≤xcr), and antiferromagnetic ordering of the Cu2+ and praseodymium ions at Néel temperatures TN(Cu) >TN(Cu)>TN(Pr) in the insulating phase (xcr≤x1). In the metallic phase, Tc decreases monotonically with x and vanishes near xcr, the dependence of Tc on pressure P and the upper critical field on temperature are both anomalous, and the low temperature specific heat can be resolved into a large γΓ contribution, reminiscent of heavy fermion behavior, and a spin Kondo anomaly; in the insulating phase, the values of TN(Pr) are anomalously large. These phenomena are briefly reviewed within the framework of a picture that is based on appreciable hybridization of the praseodymium localized 4f states and the CuO2 valence band states. A phenomenological model that incorporates the annihilation of mobile holes in the CuO2 planes and superconducting electron pair breaking by the praseodymium ions can describe Tc (x,P) for x ≤ 0.2. |
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