Fermi surface reconstruction of superoxygenated La$_2$CuO$_{4}$ with ordered oxygen interstitials

TL;DR

This study reveals how ordered oxygen interstitials in La$_2$CuO$_{4+y}$ cause Fermi surface reconstruction, leading to multiband electronic structures and enhanced superconductivity, challenging traditional rigid-band models.

Contribution

It provides detailed supercell band calculations showing the impact of oxygen interstitial ordering on Fermi surface topology and electronic properties in La$_2$CuO$_{4+y}$.

Findings

Formation of multiple Fermi surface spots with small gaps

Presence of three mini-bands crossing the Fermi level

Increased density-of-states and band mass at $E_F$

Abstract

Novel imaging methods show that the mobile dopants in optimum doped La$_2$CuO$_{4+y}$ (LCO) get self-organized, instead of randomly distributed. Rigid-band models fail because of ordering of dopants and supercell calculations are required to obtain the Fermi surface reconstruction. We have performed advanced band calculations for a large supercell La$_{16}$Cu$_8$O$_{32+N}$ where $N$=1 or 2 oxygen interstitials form rows in the spacer La$_{16}$O$_{16+N}$ layers intercalated between the CuO$_2$ layers as determined by scanning nano x-ray diffraction. The additional oc cupied states made by interstitial oxygen orbitals sit well below the Fermi level ($E_F$) and lead to hole doping as expect ed. The unexpected results show that in the heavily doped puddles the altered Cu(3d)-O(2p) band hybridization at $E_F$ indu ces a multiband electronic structure with the formation of multiple Fermi surface spots: a) small gaps appear in the folde d Fermi surface, b) three mini-bands cross $E_F$ with reduced Fermi energies of 60, 150, and 240 meV respectively, c) the d ensity-of-states and band mass at $E_F$ show substantial increases, and d) spin-polarized calculations show a moderate incr ease of antiferromagnetic spin fluctuations. All calculated features are favorable to enhance superconductivity however the comparison with experimental methods probing the average electronic structure of cuprates will require the description of the electronics of a network of multigap superconducting puddles.