Quantum Criticality in CeMIn$_{5-x}$Sn$_x$ (M = Rh, Co)

Non-Fermi liquid behavior, as characterized by a T-linear resistivity and a T log(T) behavior in specific heat, is observed in zero field in the heavy fermion system CeCoIn$_5$. The application of magnetic field has revealed a field tuned quantum critical point surprisingly coincident with the superconducting H$_{c2}$. We present data that shows the application of pressure reduces the critical field H$_{QCP}$ more rapidly than H$_{c2}$ is suppressed. We also investigate doping studies which show an anisotropically field tuned QCP in CeRhIn$_{5-x}$Sn$_x$ at x=1.0, the critical doping where antiferromagnetism is suppressed, while results on CeCoIn$_{5-x} $Sn$_x$ maintains that the quantum critical field and the superconducting upper critical field are intimately connected. We attempt to reconcile whether all the critical behavior in the CeMIn$_5$ family can have a common origin.