Chemical potential oscillations from a single nodal pocket in the underdoped high-Tc superconductor YBa2Cu3O6+x

TL;DR

This study uses second harmonic quantum oscillation measurements to demonstrate that underdoped YBa2Cu3O6+x has a single quasi-two dimensional Fermi surface pocket near the nodal region, challenging the idea of an ambipolar Fermi surface.

Contribution

It provides evidence that only one Fermi surface pocket exists in underdoped YBa2Cu3O6+x, based on chemical potential oscillation analysis, clarifying the Fermi surface topology.

Findings

Second harmonic oscillations mainly originate from chemical potential oscillations.

Evidence supports a single Fermi surface pocket, not multiple or ambipolar.

The pocket is likely near the nodal region of the Brillouin zone.

Abstract

The mystery of the normal state in the underdoped cuprates has deepened with the use of newer and complementary experimental probes. While photoemission studies have revealed solely `Fermi arcs' centered on nodal points in the Brillouin zone at which holes aggregate upon doping, more recent quantum oscillation experiments have been interpreted in terms of an ambipolar Fermi surface, that includes sections containing electron carriers located at the antinodal region. To address the question of whether an ambipolar Fermi surface truly exists, here we utilize measurements of the second harmonic quantum oscillations, which reveal that the amplitude of these oscillations arises mainly from oscillations in the chemical potential, providing crucial information on the nature of the Fermi surface in underdoped YBa2Cu3O6+x. In particular, the detailed relationship between the second harmonic amplitude and the fundamental amplitude of the quantum oscillations leads us to the conclusion that there exists only a single underlying quasi-two dimensional Fermi surface pocket giving rise to the multiple frequency components observed via the effects of warping, bilayer splitting and magnetic breakdown. A range of studies suggest that the pocket is most likely associated with states near the nodal region of the Brillouin zone of underdoped YBa2Cu3O6+x at high magnetic fields.