Quasiparticles in the vortex lattice of unconventional superconductors: Bloch waves or Landau levels?

A novel singular gauge transformation is developed for quasiparticles in the mixed state of a strongly type-II superconductor which permits a full solution of the problem at low and intermediate fields, H-c1 < B much less than H-c2. For a periodic vortex lattice the natural low-energy quasiparticle states are Bloch waves rather than Landau levels discussed in the recent literature. The new representation elucidates the physics considerably and provides fresh insights into the spectral properties of such systems. PACS numbers: 74.60.Ec, 74.72.-h.