Heat-Capacity Measurements of Energy-Gap Nodes of the Heavy-Fermion   Superconductor CeIrIn5 Deep inside the Pressure-Dependent Dome Structure of   its Superconducting Phase Diagram
  We use heat capacity measurements as a function of field rotation to identify the nodal gap structure of CeIrIn5 at pressures to 2.05 GPa, deep inside its superconducting dome. A four-fold oscillation in the heat capacity at 0.3 K is observed for all pressures but with its sign reversed between 1.50 and 0.90 GPa. On the basis of recent theoretical models for the field-angle dependent specific heat, all data, including the sign reversal, imply a d{x^2-y^2} order parameter with nodes along [110], which constrains theoretical models of the pairing mechanism in CeIrIn5. 
Xin Lu, Hanoh Lee, T. Park, F. Ronning, E. D. Bauer and J. D. Thompson
cond-mat.supr-con cond-mat.str-el