Real-space pairing through a confined local nematic state in cuprate superconductors

TL;DR

This study uncovers a confined nematic state within 4a0x4a0 plaquettes in cuprates, suggesting a local pairing mechanism for high-temperature superconductivity based on spin-resolved tunnelling measurements.

Contribution

It provides direct experimental evidence of a nematic pattern and local pairing structure in underdoped cuprates, advancing understanding of the pairing mechanism.

Findings

Nematic pattern of pairing-related states observed

Emergence of 4a0x4a0 plaquettes with doping

Precursor gap features indicating local pairing

Abstract

The pairing mechanism of high temperature superconductivity in cuprates is regarded as one of the most challenging issues that we are facing now. The core issue is about how the Cooper pairs are formed. There are plenty pictures concerning the pairing manner, and some of them postulate local pairing of charge freedom through the strong correlation effect. Here we report the spin resolved tunnelling measurements on extremely underdoped Bi2Sr2-xLaxCuO6-delta. Our data reveal that, when holes are doped into the system, the antiferromagnetic order is destroyed together with the filling up of the charge transfer gap by some density of states (DOS) with a maximum at about 200 meV. Consequently, an electronic structure with 4a0x4a0 basic plaquettes gradually emerges, and they become more populated versus further hole doping. In the central part of each plaquette, there are three unidirectional bars (along the Cu-O bond) enlightened by the enhanced peaks of coherence-like DOS at about +-25 meV, and the intensity is especially pronounced at oxygen sites. For the first time, we reveal an internal nematic pattern of these pairing related states which exhibit a feature of precursor gap for superconductivity. We argue that this confined nematic state within one 4a0x4a0 plaquette constitutes naturally the local pairing format. Our work shed new light in unraveling the longstanding puzzle of pairing mechanism in cuprate superconductors.