Describing Fluctuations in the Vortex Liquid Regime

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Abstract
A picture for vortex liquid regime in strongly type II superconductors is presented on the basis of the GL fluctuation theory developed in terms of the Landau level representation of the order parameter. It is emphasized that the critical mode, driving the melting transition and determining the phase coherence of the system, plays essential roles to low energy properties in the vortex liquid regime of extremely clean systems. Consequently, a correlation between thermodynamic and transport properties is predicted. Further, the presence of two different types of field variations, making field dependences of phenomena complicated, is pointed out, and their effects on the melting line of the vortex lattice and on physical quantities are discussed. In particular, the present theory predicts that the London-like field dependence of the melting temperature is not incompatible with the scaling behavior based on the lowest Landau mode in the vortex liquid regime, and that the melting in 90 K YBCO is always 3D-like at finite temperatures. Crucial differences between the present GL framework and models based on the London limit for the vortex liquid regime are emphasized through a calculation of tilt modulus in the liquid regime and some consideration on the linear response in the force free configuration.
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