Vortex superflow Doppler-shifts low-energy quasiparticles in a nodal superconductor. For a circular cell of radius and flow magnitude proportional to , its spatially averaged magnitude is proportional to . A linearly vanishing nodal density of states then acquires a zero-energy contribution proportional to , producing a low-temperature linear heat-capacity coefficient with that scaling. This is a clean semiclassical mixed-state estimate; the vector flow average can be zero, and disorder, screening, core states and other field effects change its range of validity.
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