Deviation from the Wiedemann-Franz law induced by nonmagnetic impurities in overdoped La(2-x)SrxCuO(4)

To investigate the validity of the Wiedemann-Franz (WF) law in disordered but metallic cuprates, the low-temperature charge and heat transport properties are carefully studied for a series of impurity-substituted and carrier-overdoped La(1.8)Sr(0.2)Cu(1-z)MzO(4) (M = Zn or Mg) single crystals. With moderate impurity substitution concentrations of z = 0.049 and 0.082 (M = Zn), the resistivity shows a clear metallic behavior at low temperature and the WF law is confirmed to be valid. With increasing impurity concentration to z = 0.13 (M = Zn) or 0.15 (M = Mg), the resistivity shows a low-T upturn but its temperature dependence indicates a finite conductivity in the T -> 0 limit. In this weakly localized metallic state, that is intentionally achieved in the overdoped regime, a negative departure from the WF law is found, which is opposite to the theoretical expectation.