Pressure Induced Metal Insulator Phase Transition in Eu$_2$Ir$_2$O$_7$

The metal to insulator phase transition of the pyrochlore iridate Eu$_2$Ir$_2$O$_7$ has been studied by means of resistivity measurements under pressure in the range 2 to 12 GPa. At ambient pressure, the system is a ``metal'' at high temperatures with a non-metallic rise of resistivity with decreasing temperature followed by a metal-insulator phase transition at T$_{MI}$ below which it becomes insulating. With increasing pressure, a cross-over from non-metallic to metallic appears in the resistivity curves at a temperature $T^*>T_{MI}$. As the pressure is further increased T$^*$ rises, T$_{MI}$ drops and the low temperature insulating phase melts into a metallic phase through a continuous transition at P $\sim$ 7.8 GPa. The high pressure metallic phase is rather curious and exhibits two characteristic features of Kondo metals: a minimum resistivity and a logarithmic rise of resistivity at low temperatures. We will show that there is a remarkable correspondence between the resistivity curves measured at various pressures and those obtained by successively replacing the R site of the R$_2$Ir$_2$O$_7$ family by larger rare earth atoms.