Pre-pairing and the "Filling" Gap in the Cuprates From the Tomographic Density of States

TL;DR

This study uses the tomographic density of states to analyze the temperature dependence of the superconducting gap in cuprates, revealing pre-formed pairs and attributing the gap filling to temperature-dependent pair-breaking rates.

Contribution

It introduces the use of TDoS for precise measurement of superconducting parameters and demonstrates the evolution of the gap and pair-breaking in cuprates across the transition.

Findings

Near-nodal gap evolves smoothly through Tc

Pre-formed pairs exist above Tc

Gap filling is due to temperature-dependent pair-breaking

Abstract

We use the tomographic density of states (TDoS), which is a measure of the density of states for a single slice through the band structure of a solid, to study the temperature evolution of the superconducting gap in the cuprates. The TDoS provides unprecedented accuracy in determining both the superconducting pair-forming strength, $\Delta$, and the pair-breaking rate, $\Gamma$. In both optimally- and under-doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$, we find the near-nodal $\Delta$ smoothly evolves through the superconducting transition temperature - clear evidence for the existence of pre-formed pairs. Additionally, we find the long observed `filling' of the superconducting gap in the cuprates is due to the strongly temperature dependent $\Gamma$.