Role of quantum fluctuations in the vortex solid to vortex liquid transition of type-II superconductors

The evolution of vortex dynamic properties along the vortex-glass melting lines, Hg (T), of epitaxial thin film Y1-x Prx Ba2 Cu3 O6.97 samples (x=0-0.4) and that of an ultrahigh purity oxygen deficient Y Ba2 Cu3 O6.5 single crystal are examined in magnetic fields up to 45 T. Analysis was carried out in the context of a modified melting line expression based on the quantum-thermal- fluctuation model of Blatter and Ivlev [Phys. Rev. B 50, 10272 (1994)]. The melting line equation developed here provides a means of experimentally determining the physical mechanism responsible for the energy scale which limits vortex motion at high frequencies. It is found that the effective vortex mass is enhanced significantly by quantum fluctuations and that the distance over which quantum fluctuations displace a segment of the vortex flux line is of the order of the size of the vortex core, which increases as T→ Tc. Supportive evidence that the equation developed here provides a universal description of the melting line in type-II superconductors is found by analyzing vortex-glass melting line data from a Mg B2 bulk sample and an amorphous α- Mox Si1-x film.