Quasi-particle interference and superconducting gap in a high-temperature superconductor Ca2-xNaxCuO2Cl2

TL;DR

This study uses spectroscopic imaging STM to analyze the superconducting gap and quasi-particle interference in Na-CCOC, revealing similarities to Bi2212 near the gap node but narrower energy ranges, shedding light on material dependence of Tc.

Contribution

First detailed QPI analysis of Na-CCOC revealing its superconducting gap characteristics and comparison with Bi2212, advancing understanding of material dependence in high-Tc cuprates.

Findings

SG dispersion near the node is similar to Bi2212 at the same doping

Na-CCOC's SG is confined to narrower energy and momentum ranges

Material dependence of Tc is partly explained by these differences

Abstract

High-transition-temperature (high-Tc) superconductivity is ubiquitous in the cuprates containing CuO2 planes but each cuprate has its own character. The study of the material dependence of the d-wave superconducting gap (SG) should provide important insights into the mechanism of high-Tc. However, because of the 'pseudogap' phenomenon, it is often unclear whether the energy gaps observed by spectroscopic techniques really represent the SG. Here, we report spectroscopic imaging scanning tunneling microscopy (SI-STM) studies of nearly-optimally-doped Ca2-xNaxCuO2Cl2 (Na-CCOC) with Tc = 25 ~ 28 K. They enable us to observe the quasi-particle interference (QPI) effect in this material, through which unambiguous new information on the SG is obtained. The analysis of QPI in Na-CCOC reveals that the SG dispersion near the gap node is almost identical to that of Bi2Sr2CaCu2Oy (Bi2212) at the same doping level, while Tc of Bi2212 is 3 times higher than that of Na-CCOC. We also find that SG in Na-CCOC is confined in narrower energy and momentum ranges than Bi2212. This explains at least in part the remarkable material dependence of Tc