Fermi-surface pockets in $YBa_2Cu_3O_{6.5}$ : A comparison of ab initio techniques

TL;DR

This study compares different ab initio methods to analyze the Fermi surface of YBa2Cu3O6.5, finding no definitive evidence of Fermi surface pockets in this phase, implying other phases may be responsible.

Contribution

It provides a comparative analysis of GGA, GGA+U, and PSIC techniques on the Fermi surface, highlighting the absence of pockets in these calculations.

Findings

No pockets found in GGA+U and PSIC calculations.

Minor pockets appear only when shifting the Fermi level.

Fermi surface pockets likely originate from other phases.

Abstract

We study the Fermi surface of metallic, non-magnetic \textit{ortho}-II YBa$_2$Cu$_3$O$_{6.5}$ using three different density-functional-based band-structure techniques (GGA, GGA+U, PSIC). The calculated Fermi surface exhibits no pockets in GGA+U and PSIC, a minor one in GGA. Upon shifting the Fermi level in the vicinity of the calculated value, we instead observe several pocket structures. We calculate their cross-sectional areas and cyclotron masses. Overall, our calculations show no solid evidence of the existence of electron-like --nor, in fact, of any-- Fermi surface pockets in this phase. This suggests that the origin of the pockets should be sought for in other, different phases.