Comment on Multiple Quantum Oscillations in the de Haas - van Alphen Spectra of the Underdoped High-Temperature Superconductor YBa2Cu3O6.5 (A. Audouard et al., Phys. Rev. Lett. 103 (2009) 157003)

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.