Uniaxial Pressure and the Superconducting Transition of CeIrIn$_5$

We measure the superconducting transition temperature of CeIrIn$_5$ with applied uniaxial pressure. Heat capacity shows almost no shift in T$_c$ as pressure is applied along the {\em c}-axis, contrary to the large decrease expected from earlier thermal expansion measurements. With {\em a}-axis pressure, however, T$_c$ increases about 20 mK per kbar. These results indicate that another factor besides the {\em c}/{\em a} ratio has a strong effect on T$_c$. Furthermore, applied pressure along either crystal axis strongly reduces the size of the heat capacity transition. We will also discuss the effect of uniaxial pressure on the resistive transtition, which at ambient pressure occurs at a temperature well above the heat capacity transition. Finally, we present x-ray diffraction measurements correlating our applied pressures with changes in the crystal lattice constants.