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I now discuss some general features of the vortex-quasiparticle interaction. While some of the details below are specific for the magnetic field induced vortex state of a d$_{x^2-y^2}$ superconductor, the discussion is readily generalized to other unconventional (and s-wave!) superconductors and to the thermal or quantum vortex-antivortex pair fluctuations. The interaction between vortices and quasiparticles involves TWO key ingredients: first, there is a Doppler shift effect, just as inferred on semiclassical grounds (Volovik '93, Sauls '92). However, there is also an additional, purely quantum mechanical contribution: a quasiparticle going around a vortex experiences a "Berry phase" effect, its phase winding via the Aharonov-Bohm scattering by $\pm\pi$ ON TOP of the Doppler shift contribution. This is a fundamental quantum mechanical consequence of the simple fact that vortices represent topological defects of the field which carries charge $2e$, while the original fermions carry charge $e$. BOTH contributions must be included whenever quasiparticles maintain phase coherence over distances larger than average separation between vortices. Note that the topological Aharonov-Bohm terms arise ONLY in presence of vortices! They are absent for topologically trivial configurations of $\Delta ({\vec r})$.

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