Momentum dependence of the energy gap in the superconducting state of optimally doped Bi2(Sr,R)2CuOy (R=La and Eu)

TL;DR

This study uses ARPES to investigate the momentum dependence of the energy gap in optimally doped Bi2(Sr,R)2CuOy, revealing a d-wave gap near the node and a pseudogap behavior near the antinode, with R-dependent variations.

Contribution

It provides detailed momentum-resolved measurements of the energy gap, distinguishing between the superconducting gap and pseudogap in optimally doped cuprates.

Findings

The gap near the node follows a monotonic d-wave form at low temperatures.

The R=La sample has a larger gap correlating with higher Tc.

An abrupt deviation from the d-wave behavior occurs near the antinode, indicating pseudogap phenomena.

Abstract

The energy gap of optimally doped Bi2(Sr,R)2CuOy (R=La and Eu) was probed by angle resolved photoemission spectroscopy (ARPES) using a vacuum ultraviolet laser (photon energy 6.994 eV) or He I resonance line (21.218 eV) as photon source. The results show that the gap around the node at sufficiently low temperatures can be well described by a monotonic d-wave gap function for both samples and the gap of the R=La sample is larger reflecting the higher Tc. However, an abrupt deviation from the d-wave gap function and an opposite R dependence for the gap size were observed around the antinode, which represent a clear disentanglement between the antinodal pseudogap and the nodal superconducting gap.