Doping Dependence of the Pressure Response of Tc in the SmO1-xFxFeAs Superconductors

The superconducting transition temperature of the high-Tc SmO1-xFxFeAs superconductors increases monotonically as the F-doping level x increases to 0.20. High-pressure magnetization experiments reveal a strong sensitivity of Tc to interatomic distances in the underdoped regime (x </= 0.12) with the pressure coefficient of Tc, d(ln Tc)/dP being strongly positive. However, as the doping level increases further to x = 0.15, we find that this sensitivity is strongly suppressed and at the same time, d(ln Tc)/dP sharply switches over to assume negative values with Tc decreasing with increasing applied pressure. The abrupt change in the pressure response of the superconducting properties of the SmO1-xFxFeAs phases coincides with the putative existence of a quantum critical point (QCP) near x approximately 0.14, as proposed by resistivity and Hall effect measurements.