Controlling the self-doping of YBa2C3O7-d polar surfaces: From Fermi surface to nodal Fermi arcs by ARPES

TL;DR

This study uses ARPES with potassium surface doping to investigate how the Fermi surface in YBa2Cu3O7-d changes from a normal metal to disconnected arcs or pockets in the underdoped regime, clarifying surface doping effects.

Contribution

It demonstrates a method to control surface doping in YBCO via potassium deposition, revealing the evolution of Fermi surface topology in underdoped cuprates.

Findings

Fermi surface collapses into disconnected arcs in underdoped YBCO.

Potassium doping allows continuous tuning from overdoped to underdoped regimes.

Surface self-doping affects ARPES measurements and can be controlled experimentally.

Abstract

The discovery of quantum oscillations in the normal-state electrical resistivity of YBa2Cu3O6.5 provides the first evidence for the existence of Fermi surface (FS) pockets in an underdoped cuprate. However, the pockets' electron vs. hole character, and the very interpretation in terms of closed FS contours, are the subject of considerable debate. Angle-resolved photoemission spectroscopy (ARPES), with its ability to probe electronic dispersion as well as the FS, is ideally suited to address this issue. Unfortunately, the ARPES study of YBa2C3O7-d (YBCO) has been hampered by the technique's surface sensitivity. Here we show that this stems from the polarity and corresponding self-doping of the YBCO surface. By in-situ deposition of potassium atoms on the cleaved surface, we are able to continuously tune the doping of a single sample from the heavily overdoped to the underdoped regime. This reveals the progressive collapse of the normal-metal-like FS into four disconnected nodal FS arcs, or perhaps into hole but not electron pockets, in underdoped YBCO6.5.