The normal state in the hole underdoped copper oxide superconductors has proven to be a source of mystery for decades. The measurement of a small Fermi surface by quantum oscillations on suppression of superconductivity by high applied magnetic fields, together with complementary spectroscopic measurements in the hole underdoped copper oxide superconductors, point to a nodal electron pocket from charge order in YBa2Cu3(6+δ). Here, we report quantum oscillation measurements in the closely related stoichiometric material YBa2Cu4O8, which reveals similar Fermi surface properties to YBa2Cu3(6+δ), despite the nonobservation of charge order signatures in the same spectroscopic techniques, such as X-ray diffraction, that revealed signatures of charge order in YBa2Cu3(6+δ). Fermi surface reconstruction in YBa2Cu4O8 is suggested to occur from magnetic field enhancement of charge order that is rendered fragile in zero magnetic fields because of its potential unconventional nature and/or its occurrence as a subsidiary to more robust underlying electronic correlations.B.T., A.S, and S.E.S. acknowledge support from the
Royal Society, the Winton Programme for the Physics of
Sustainability, and the European Research Council under
the European Unions Seventh Framework Programme
(grant number FP/2007-2013)/ ERC Grant Agreement
number 337425. N.H., Z.Z., F.F.B., and B.J.R. acknowl-
edge support for high-magnetic-field experiments from
the US Department of Energy, Office of Science, BES-
MSE `Science of 100 Tesla' programme. G.G.L. acknowl-
edges support from EPSRC grant EP/K012894/1. Work
at NIU was supported by The Institute for Nanoscience,
Engineering, and Technology - InSET. A portion of this
work was performed at the National High Magnetic Field
Laboratory, which is supported by NSF co-operative
agreement number DMR-0654118, the state of Florida,
and the DOE. We are grateful for the experimental assis-
tance provided by National High Magnetic Field Labora-
tory personnel, including J. B. Betts, Y. Coulter, M. Gor-
don, C. H. Mielke, A. Parish, R. McDonald, D. Rickel,
and D. Roybal.This is the author accepted manuscript. The final version is available from the National Academy of Sciences via http://dx.doi.org/10.1073/pnas.150416411
