Effect of Zn doping in under- and over-doped LaFe1−xCoxAsO system

We study the effect of nonmagnetic Zn impurity on superconductivity in the Co-doped LaFe1−x−yCoxZnyAsO system. A light Zn doping drastically suppresses the superconducting transition temperature for both under- and over-doped superconductors. This is consistent with the theoretical prediction within the scenario of s±-wave or d-wave pairings. The rate of the Tc decrease, , is substantially smaller in the under-doped regime than in the over-doped regime. We propose that the less drastic Tc reduction in the under-doped superconductor is due to the suppression of a competing antiferromagnetic order, which is in favor of superconductivity.