Nodeless pairing in superconducting copper-oxide monolayer films on Bi2Sr2CaCu2O8+{\delta}

TL;DR

This study reveals a nodeless s-wave superconducting gap in CuO2 monolayer films on Bi2Sr2CaCu2O8+{ extdelta}, providing new insights into high-temperature superconductivity mechanisms.

Contribution

It demonstrates the existence of a nodeless superconducting gap in CuO2 layers, supporting an s-wave pairing symmetry in high-Tc cuprates.

Findings

Identification of a nodeless U-like superconducting gap.

Observation of strong phase coherence and immunity to impurity scattering.

Correlation of the gap with s-wave superconductivity in cuprates.

Abstract

The pairing mechanism of high-temperature superconductivity in cuprates remains the biggest unresolved mystery in condensed matter physics. To solve the problem, one of the most effective approaches is to investigate directly the superconducting CuO2 layers. Here, by growing CuO2 monolayer films on Bi2Sr2CaCu2O8+{\delta} substrates, we identify two distinct and spatially separated energy gaps centered at the Fermi energy, a smaller U-like gap and a larger V-like gap on the films, and study their interactions with alien atoms by low-temperature scanning tunneling microscopy. The newly discovered U-like gap exhibits strong phase coherence and is immune to scattering by K, Cs and Ag atoms, suggesting its nature as a nodeless superconducting gap in the CuO2 layers, whereas the V-like gap agrees with the well-known pseudogap state in the underdoped regime. Our results support an s-wave superconductivity in Bi2Sr2CaCu2O8+{\delta}, which, we propose, originates from the modulation-doping resultant two-dimensional hole liquid confined in the CuO2 layers.