Superconducting gap in the presence of bilayer splitting in underdoped Bi(Pb)2212

TL;DR

This study investigates the superconducting gap in underdoped Bi(Pb)2212, revealing that bonding and antibonding Fermi surface sheets have identical gaps and identifying deviations from simple gap models.

Contribution

It provides the first detailed comparison of superconducting gaps on split Fermi surface sheets in underdoped Bi(Pb)2212, showing their equivalence and mapping the k-dependence of the gap.

Findings

Bonding and antibonding Fermi surface sheets have identical superconducting gaps.

The k-dependence of the gap deviates from simple cos(kx)-cos(ky) models.

Experimental tuning reveals detailed gap structure.

Abstract

The clearly resolved bilayer splitting in ARPES spectra of the underdoped Pb-Bi2212 compound rises the question of how the bonding and antibonding sheets of the Fermi surface are gapped in the superconducting state. Here we compare the superconducting gaps for both split components and show that within the experimental uncertainties they are identical. By tuning the relative intensity of the bonding and antibonding bands using different excitation conditions we determine the precise {\bf k}-dependence of the leading edge gap. Significant deviations from the simple cos($k_{x}$)-cos($k_{y}$) gap function for the studied doping level are detected.