Emergent normal fluid in the superconducting ground state of overdoped cuprates

TL;DR

This study reveals that in overdoped cuprates, a normal fluid component emerges from pair-breaking scattering, disrupting superconductivity and leading to a distinct quasiparticle interference pattern observable via scanning tunneling spectroscopy.

Contribution

It provides evidence that the emergence of a normal fluid from pair-breaking scattering explains the suppression of superconductivity in overdoped cuprates.

Findings

Quasiparticle interference wavevector appears at zero bias in overdoped regime.

The interference pattern is consistent with scattering of gapless normal carriers.

Normal fluid component is mainly located at the antinodes and is temperature independent.

Abstract

The microscopic mechanism for the disappearance of superconductivity in overdoped cuprates is still under heated debate. Here we use scanning tunneling spectroscopy to investigate the evolution of quasiparticle interference phenomenon in $\rm Bi_2Sr_2CuO_{6+\delta}$ over a wide range of hole densities. We find that when the system enters the overdoped regime, a peculiar quasiparticle interference wavevector with quarter-circle pattern starts to emerge even at zero bias, and its intensity grows with increasing doping level. Its energy dispersion is incompatible with the octet model for d-wave superconductivity, but is highly consistent with the scattering interference of gapless normal carriers. The weight of the gapless quasiparticle interference is mainly located at the antinodes and is independent of temperature. We propose that the normal fluid emerges from the pair-breaking scattering between flat antinodal bands in the quantum ground state, which is the primary cause for the reduction of superfluid density and suppression of superconductivity in overdoped cuprates.