  Recent observations of slow magneto-oscillations in some underdoped cuprate
superconductors are one of the most striking discoveries in the field of
superconductivity since many probes of underdoped cuprates clearly point to a
non Fermi-liquid normal state. We show that a large magnitude and strong
magnetic-field dependence of the residual resistance invalidate the
conventional interpretation of the magneto-oscillations as a normal-state dHvA
effect. We propose that the oscillations are most likely caused by a quantum
interference of vortex and crystal lattice modulations of the order parameter
in the mixed superconducting state.
