Magnetic quantum oscillations in YBa$_2$Cu$_3$O$_{6.61}$ and YBa$_2$Cu$_3$O$_{6.69}$ in fields of up to 85 T; patching the hole in the roof of the superconducting dome

TL;DR

This study investigates magnetic quantum oscillations in underdoped YBa₂Cu₃O₆+x, revealing Fermi energy behavior and potential phase transitions near specific doping levels, thus addressing gaps in understanding the cuprate superconducting dome.

Contribution

It provides new measurements of quantum oscillations in underdoped cuprates at high magnetic fields, suggesting critical points and phase transitions related to Fermi surface changes.

Findings

Fermi energy peaks at doping p≈0.11-0.12

Effective mass may diverge near phase transitions

Evidence of a topological transition in Fermi surface

Abstract

We measure magnetic quantum oscillations in the underdoped cuprates YBa$_2$Cu$_3$O$_{6+x}$ with $x=0.61$, 0.69, using fields of up to 85 T. The quantum-oscillation frequencies and effective masses obtained suggest that the Fermi energy in the cuprates has a maximum at $p\approx 0.11-0.12$. On either side, the effective mass may diverge, possibly due to phase transitions associated with the T=0 limit of the metal-insulator crossover (low-$p$ side), and the postulated topological transition from small to large Fermi surface close to optimal doping (high $p$ side).