Comment on "Apical charge flux-modulated in-plane transport properties of cuprate superconductors"

TL;DR

This paper critiques a recent claim linking apical charge flux to higher critical temperatures in cuprates, showing that the trend is actually part of a longer-known correlation involving electronic hopping and orbital energies.

Contribution

It clarifies that the observed trend is not new and is encompassed within established correlations involving the axial orbital energy and electron hopping.

Findings

The claimed trend is included in the long-known correlation from 2001.

The correlation is related to the energy of the axial orbital, not just apical oxygen distance.

The paper emphasizes the importance of orbital hybridization in superconducting properties.

Abstract

The abstract of Phys. Rev. Lett. 121, 157001 (2018) claims to "demonstrate, using ab initio computations, a new trend suggesting that the cuprates with stronger out-of-CuO$_{2}$-plane chemical bonding between the apical anion (O, Cl) and apical cation (e.g., La, Hg, Bi, Tl) are generally correlated with higher $T_{c\,\max}$ in experiments". We point out that this trend is included in the long-known [Phys. Rev. Lett. 87, 047003 (2001)] correlation of $T_{c\,\max}$ with the hopping range of the electrons at (the most interlayer-bonding sheet of) the Fermi-surface. Contrary to the impression given in Phys. Rev. Lett. 121, 157001 (2018), the correlation mentioned in Phys. Rev. Lett. 87, 047003 (2001) is not simply with the distance, $d_{A},$ of apical oxygen from the nearest CuO$_{2}$ plane; but rather, as stated in the abstract of Phys. Rev. Lett. 87, 047003 (2001), "It is controlled by the energy of the axial orbital, a hybrid between Cu 4$s$, apical-oxygen 2$p_{z},$ and farther orbitals."