  Dynamic resistance spectra of ramp junctions made of underdoped YBCO
electrodes and Ga-doped YBCO barrier are reported. Series of equidistant peaks
were observed in these spectra in junctions oriented along the node direction.
Junctions with different barrier thickness d_N, showed that the distance
between adjacent peaks scales inversely with d_N. The peaks were thus
identified as due to McMillan-Rowell like oscillations in the barrier. Analysis
of the series of peaks yields an upper limit of about 3.7 meV on the value of
the energy gap along the node. We attribute this small gap to the complex s
component of the order parameter of underdoped YBCO near the interface of the
junctions.
