Relationship between the parent charge transfer gap and maximum transition temperature in cuprates

TL;DR

This study reveals a strong anticorrelation between the charge transfer gap and maximum transition temperature in cuprates, suggesting the gap's key role in high-temperature superconductivity.

Contribution

It provides new experimental evidence linking the charge transfer gap size to Tc,max across different cuprate families, advancing understanding of the superconducting mechanism.

Findings

Double-layer cuprates have smaller charge transfer gaps than single-layer counterparts.

Smaller charge transfer gaps correlate with higher maximum transition temperatures.

Results support the importance of the charge transfer gap in high-Tc superconductivity.

Abstract

One of the biggest puzzles concerning the cuprate high temperature superconductors is what determines the maximum transition temperature (Tc,max), which varies from less than 30 K to above 130 K in different compounds. Despite this dramatic variation, a robust trend is that within each family, the double-layer compound always has higher Tc,max than the single-layer counterpart. Here we use scanning tunneling microscopy to investigate the electronic structure of four cuprate parent compounds belonging to two different families. We find that within each family, the double layer compound has a much smaller charge transfer gap size ($\Delta_{CT}$), indicating a clear anticorrelation between $\Delta_{CT}$ and Tc,max. These results suggest that the charge transfer gap plays a key role in the superconducting physics of cuprates, which shed important new light on the high Tc mechanism from doped Mott insulator perspective.