Observation of McMillan-Rowell like oscillations in underdoped YBCO junctions oriented along the node of the d-wave order parameter

TL;DR

This study reports the observation of McMillan-Rowell like oscillations in underdoped YBCO junctions, revealing insights into the energy gap along the node and the complex s component of the order parameter.

Contribution

It provides experimental evidence of McMillan-Rowell oscillations in underdoped YBCO junctions and estimates the energy gap along the node.

Findings

Equidistant peaks observed in dynamic resistance spectra.

Peak spacing scales inversely with barrier thickness.

Estimated energy gap along the node is about 3.7 meV.

Abstract

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.