Origins of large critical temperature variations in single layer cuprates

TL;DR

This study compares the electronic structures of two single-layer cuprate superconductors with different maximum critical temperatures, identifying key differences in their Fermi surfaces and lattice distortions that may influence their superconducting properties.

Contribution

It provides new insights into how structural and electronic differences in single-layer cuprates relate to their critical temperatures, using ARPES analysis.

Findings

Absence of shadow band in Tl2201 correlates with higher T_c.

Tl2201's Fermi surface has long straight anti-nodal regions.

Differences in anti-nodal band dispersion may influence pairing strength.

Abstract

We study the electronic structures of two single layer superconducting cuprates, Tl$_2$Ba$_2$CuO$_{6+\delta}$ (Tl2201) and (Bi$_{1.35}$Pb$_{0.85}$)(Sr$_{1.47}$La$_{0.38}$)CuO$_{6+\delta}$ (Bi2201) which have very different maximum critical temperatures (90K and 35K respectively) using Angular Resolved Photoemission Spectroscopy (ARPES). We are able to identify two main differences in their electronic properties. First, the shadow band that is present in double layer and low T$_{c,max}$ single layer cuprates is absent in Tl2201. Recent studies have linked the shadow band to structural distortions in the lattice and the absence of these in Tl2201 may be a contributing factor in its T$_{c,max}$.Second, Tl2201's Fermi surface (FS) contains long straight parallel regions near the anti-node, while in Bi2201 the anti-nodal region is much more rounded. Since the size of the superconducting gap is largest in the anti-nodal region, differences in the band dispersion at the anti-node may play a significant role in the pairing and therefore affect the maximum transition temperature.