Point nodes persisting far beyond Tc in Bi2212

TL;DR

This study uses high-resolution laser ARPES to show that point nodes in Bi2212 persist well above Tc, indicating preformed pairs and challenging the traditional view of nodal gap collapse at Tc in cuprates.

Contribution

It provides direct experimental evidence that point nodes survive beyond Tc in Bi2212, supporting the preformed pair scenario in high-temperature superconductors.

Findings

Point nodes persist far above Tc in Bi2212.

Superconductivity onset linked to pair breaking rate being less than single particle scattering rate.

Nodal gap behavior challenges BCS-like collapse at Tc in cuprates.

Abstract

In contrast to a complex feature of antinodal state, suffering from competing order(s), the "pure" pairing gap of cuprates is obtained in the nodal region, which therefore holds the key to the superconducting mechanism. One of the biggest question is whether the point nodal state as a hallmark of d-wave pairing collapses at Tc like the BCS-type superconductors, or it instead survives above Tc turning into the preformed pair state. A difficulty in this issue comes from the small magnitude of the nodal gap, which has been preventing experimentalists from solving it. Here we use a laser ARPES capable of ultrahigh energy resolution, and detect the point nodes surviving far beyond Tc in Bi2212. By tracking the temperature evolution of spectra, we reveal that the superconductivity occurs when the pair breaking rate is suppressed smaller than the single particle scattering rate on cooling, which governs the value of Tc in cuprates.