Observation of a d-wave nodal liquid in highly underdoped Bi_2Sr_2CaCu_2O_{8+\delta}

TL;DR

This study reveals a non-superconducting nodal liquid state in underdoped Bi_2Sr_2CaCu_2O_{8+eta} with a d-wave gap structure, providing insights into the emergence of high-temperature superconductivity.

Contribution

It identifies a nodal liquid state with d-wave symmetry in the underdoped regime, bridging the gap between insulator and superconductor phases.

Findings

The non-superconducting state has a d-wave-like gap structure.

Spectral evolution suggests a continuous transition to superconductivity.

High temperature superconductivity emerges with quantum phase coherence in a nodal liquid.

Abstract

We use angle resolved photoemission spectroscopy to probe the electronic excitations of the non-superconducting state that exists between the antiferromagnetic Mott insulator at zero doping and the superconducting state at larger dopings in Bi_2Sr_2CaCu_2O_{8+\delta}. We find that this state is a nodal liquid whose excitation gap becomes zero only at points in momentum space. Despite exhibiting a resistivity characteristic of an insulator and the absence of coherent quasiparticle peaks, this material has the same gap structure as the d-wave superconductor. We observe a smooth evolution of the spectrum across the insulator-to-superconductor transition, which suggests that high temperature superconductivity emerges when quantum phase coherence is established in a non-superconducting nodal liquid.