Evidence for a small hole pocket in the Fermi surface of underdoped YBa2Cu3Oy.

N Doiron-Leyraud,D Vignolles,D Leboeuf,F Laliberté,J.-H Park,D A Bonn,C Proust,B J Ramshaw,S Badoux,B Vignolle,E Hassinger,L Taillefer,R Liang,W N Hardy,S René De Cotret,S Lepault

doi:10.1038/ncomms7034

Abstract

In underdoped cuprate superconductors, the Fermi surface undergoes a reconstruction that produces a small electron pocket, but whether there is another, as yet, undetected portion to the Fermi surface is unknown. Establishing the complete topology of the Fermi surface is key to identifying the mechanism responsible for its reconstruction. Here we report evidence for a second Fermi pocket in underdoped YBa2Cu3Oy, detected as a small quantum oscillation frequency in the thermoelectric response and in the c-axis resistance. The field-angle dependence of the frequency shows that it is a distinct Fermi surface, and the normal-state thermopower requires it to be a hole pocket. A Fermi surface consisting of one electron pocket and two hole pockets with the measured areas and masses is consistent with a Fermi-surface reconstruction by the charge–density–wave order observed in YBa2Cu3Oy, provided other parts of the reconstructed Fermi surface are removed by a separate mechanism, possibly the pseudogap.

Highlights

In underdoped cuprate superconductors, the Fermi surface undergoes a reconstruction that produces a small electron pocket, but whether there is another, as yet, undetected portion to the Fermi surface is unknown
Fermi-surface reconstruction and charge–density– wave (CDW) modulations are two universal signatures of underdoped cuprates, which begs the following question: is the Fermi surface seen by quantum oscillations compatible with a reconstruction by the observed CDW modulations? This issue requires a detailed knowledge of the Fermi surface, to be compared with Fermi surface calculations based on the measured parameters of the CDW order, in the same material at the same doping
A Fermi surface consisting of one electron and two hole pockets of the measured sizes and masses is consistent with a reconstruction by the observed CDW

Summary

Introduction

The Fermi surface undergoes a reconstruction that produces a small electron pocket, but whether there is another, as yet, undetected portion to the Fermi surface is unknown. In YBCO, a thermodynamic signature of the CDW order was detected in the sound velocity at low temperature and finite magnetic field[15] These CDW modulations are reminiscent of the checkerboard pattern previously observed by STM on Bi2Sr2CaCu2O8 þ d (refs 16,17), for instance. This issue requires a detailed knowledge of the Fermi surface, to be compared with Fermi surface calculations based on the measured parameters of the CDW order, in the same material at the same doping. In this Article, we report quantum oscillations measurements that reveal an additional, hole-like Fermi pocket in underdoped YBCO.

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Conclusion