Field Induced Nodal Order Parameter in the Tunneling Spectrum of   YBa$_2$Cu$_3$O$_{7-x}$ Superconductor
  We report planar tunneling measurements on thin films of YBa$_2$Cu$_3$O$_{7-x}$ at various doping levels under magnetic fields. By choosing a special setup configuration, we have probed a field induced energy scale that dominates in the vicinity of a node of the d-wave superconducting order parameter. We found a high doping sensitivity for this energy scale. At Optimum doping this energy scale is in agreement with an induced $id_{xy}$ order parameter. We found that it can be followed down to low fields at optimum doping, but not away from it. 
G. Leibovitch, R. Beck, Y. Dagan, S. Hacohen and G. Deutscher