  We propose a quantum oscillation experiment by which the rotation of an
underdoped YBa2Cu3O6+x sample about two different axes with respect to the
orientation of the magnetic field can be used to infer the shape of the
in-plane cross-section of corrugated Fermi surface cylinder(s). Deep
corrugations in the Fermi surface are expected to give rise to nodes in the
quantum oscillation amplitude that depend on the magnitude and orientation of
the magnetic induction B. Because the symmetry of electron and hole cyclinders
within the Brillouin zone are expected to be very different, the topology can
provide essential clues as to the broken symmetry responsible for the observed
oscillations.
