Protected nodes and the collapse of the Fermi arcs in high Tc cuprates

TL;DR

This study shows that in underdoped cuprates, the superconducting gap remains unchanged with temperature up to Tc, and the formation of Fermi arcs at Tc signifies a phase transition rather than thermal broadening.

Contribution

It reveals that the superconducting gap's magnitude and anisotropy are temperature-independent up to Tc, and links Fermi arc formation to the pseudogap phase transition.

Findings

Superconducting gap is temperature-independent up to Tc.

Fermi arcs form abruptly at Tc, not due to thermal broadening.

Fermi arcs are a signature of the pseudogap phase.

Abstract

Angle resolved photoemission on underdoped Bi2Sr2CaCu2O8 reveals that the magnitude and d-wave anisotropy of the superconducting state energy gap are independent of temperature all the way up to Tc. This lack of T variation of the entire k-dependent gap is in marked contrast to mean field theory. At Tc the point nodes of the d-wave gap abruptly expand into finite length ``Fermi arcs''. This change occurs within the width of the resistive transition, and thus the Fermi arcs are not simply thermally broadened nodes but rather a unique signature of the pseudogap phase.