The in plane normal state resistivity of a variety of underdoped cuprates is analysed in terms of a percolation model where carriers tunnel between metallic islands distributed in an insulating background. Exponential laws of the form r=roexp(To/T)a where the exponent a changes from1/4 at low temperature to ½ at higher temperatures are found to ﬁt accurately the experimental data. The results are shown to be consistent with superconducting islands of size <100A and high Tc of order 100K, together with larger islands in the normal state embedded in an insulating matrix.
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