Pressure effect on superconductivity in CeCoIn5-xSnx studied by thermal expansion

We present low-temperature thermal expansion measurements on the Sn-substituted heavy fermion superconductor CeCoIn5-xSnx for 0=<x=<0.12 in which Tc is rapidly suppressed from 2.3 (x=0) to 0.7K (x=0.12). The analysis of the superconducting transition anomalies reveals a drastic change of the uniaxial pressure dependences of Tc with Sn substitution. The hydrostatic pressure dependence of Tc is positive for Sn concentrations x=<0.06 and changes sign at larger x. A first-order superconducting transition, caused by Pauli limiting in magnetic fields that suppress Tc to below 0.7K, is visible at x=<0.06