Quantum Criticality and Superconductivity in SmFe1−xCoxAsO

Abstract

One of the iron pnictide superconductors, SmFe1−xCoxAsO shows a domelike TC curve against Co concentration x. The parent compound SmFeAsO shows the crystal structure transition and antiferromagnetic spin density wave (SDW) ordering. With increasing x, the structural transition temperature TD and SDW ordering temperature TN decrease and reach 0 K at the critical concentration xC. It is not so clear that the critical concentrations for TD and for TN coincident to each other or not. In our present report, we investigated the structural transition by the low temperature x-ray diffraction and the SDW ordering and the superconducting transition by measuring the magnetization using the SQUID magnetometer, MPMS We determined the phase diagram of TD, TN and the superconductive transition temperature TC against the Co concentration x near the xC precisely. We found that the maximum of TC in domelike shape locates near the xC, suggesting the QCP.