# Distinct Superconducting Gap on Two Bilayer-Split Fermi Surface Sheets in $Bi_2Sr_2CaCu_2O_{8+\delta}$ Superconductor

## TL;DR

This study uses high-resolution laser ARPES to reveal distinct superconducting gaps on two bilayer-split Fermi surface sheets in overdoped Bi-2212, highlighting layer-dependent superconductivity and Fermi surface effects.

## Contribution

First direct observation of different superconducting gap sizes on bilayer-split Fermi surface sheets in Bi-2212, linking Fermi surface topology to superconductivity.

## Key findings

- Different doping levels for bonding and antibonding sheets.
- Superconducting gap on antibonding sheet follows d-wave symmetry.
- Maximum gap difference near antinodal region is ~2 meV.

## Abstract

High resolution laser-based angle-resolved photoemission measurements were carried out on an overdoped $Bi_2Sr_2CaCu_2O_{8+\delta}$ superconductor with a Tc of 75 K. Two Fermi surface sheets caused by bilayer splitting are clearly identified with rather different doping levels: the bonding sheet corresponds to a doping level of 0.14 which is slightly underdoped while the antibonding sheet has a doping of 0.27 that is heavily overdoped, giving an overall doping level of 0.20 for the sample. Different superconducting gap sizes on the two Fermi surface sheets are revealed for the first time. The superconducting gap on the antibonding Fermi surface sheet follows a standard d-wave form while it deviates from the standard d-wave form for the bonding Fermi surface sheet. The maximum gap difference between the two Fermi surface sheets near the antinodal region is $\sim$2 meV. These observations provide important information for studying the relationship between the Fermi surface topology and superconductivity, and the layer-dependent superconductivity in high temperature cuprate superconductors.