Quantum oscillations in underdoped YBa_2Cu_3O_6.5

TL;DR

This study reports quantum oscillation measurements in underdoped YBa2Cu3O6.51, revealing small Fermi pockets and confirming a coherent Fermi surface, indicating a significant change in Fermi surface topology across the cuprate phase diagram.

Contribution

First observation of quantum oscillations in underdoped YBa2Cu3O6.51 confirming a coherent Fermi surface and small Fermi pockets.

Findings

Low frequency F = 530 T indicating small Fermi pockets

Agreement with Lifshitz-Kosevitch theory

Contrast with overdoped cuprates showing large Fermi surfaces

Abstract

Shubnikov-de Haas and de Haas-van Alphen effects have been measured in the underdoped high temperature superconductor YBa$_2$Cu$_3$O$_{6.51}$. Data are in agreement with the standard Lifshitz-Kosevitch theory, which confirms the presence of a coherent Fermi surface in the ground state of underdoped cuprates. A low frequency $F = 530 \pm 10$ T is reported in both measurements, pointing to small Fermi pocket, which corresponds to 2% of the first Brillouin zone area only. This low value is in sharp contrast with that of overdoped Tl$_2$Ba$_2$CuO$_{6+\delta}$, where a high frequency $F = 18$ kT has been recently reported and corresponds to a large hole cylinder in agreement with band structure calculations. These results point to a radical change in the topology of the Fermi surface on opposing sides of the cuprate phase diagram.