Loss of Superconducting Phase Coherence inYBa2Cu3O7Films: Vortex-Loop Un

Abstract

The linear conductance G' + iG(") parallel to the CuO(2) planes of flat d = 50-600 nm thin films is measured between 30 mHz and 800 kHz. The decay of the phase-coherent superfluid density signals the proliferation of 3D vortex loops which terminates at T*<T(c), where omegaG"(T*) attains 35(5) nH(-1) being independent of d. We ascribe this novel transition to the blowout of loops which reach the film thickness. Above T(c), G(omega) appears to be determined by unbound vortex lines thermally excited in a 2D phase-incoherent superfluid showing features previously being associated with a Kosterlitz-Thouless transition.

Mapping Dynamical Magnetic Responses of Ultrathin Micron-Size Superconducting Films Using Nitrogen-Vacancy Centers in Diamond

“…Such discrepancy was commonly observed in measurements of ac magnetic responses of ultra-thin SC films. 3,29,30 It is generally understood to be a 2D effect due to diffusive motion of thermally excited vortexantivortex. 3,6 Presumably because of reduced pinning or viscosity, the vortex-antivortex excitations are more diffusive for thinner SC films.…”

“…The theory agrees with experiment below ∼72 K but obviously disagrees in the range between 72 and 91 K ( T c ). Such discrepancy was commonly observed in measurements of ac magnetic responses of ultrathin SC films. ,, It is generally understood to be a 2D effect due to diffusive motion of thermally excited vortex–antivortex. , Presumably because of reduced pinning or viscosity, the vortex–antivortex excitations are more diffusive for thinner SC films. , The diffusion reduces the supercurrent induced by the applied magnetic field. − Accordingly, the diamagnetic response of the SC thin film is greatly suppressed until the temperature is sufficiently low such that the vortex–antivortex diffusive motion becomes insignificant. ,, Previous theoretical calculation and simulation have confirmed the “delayed” Meissner effect. ,, However, quantitative evaluation on the difference between T c and T * would require the knowledge of pinning energy and temperature-dependent diffusion coefficient of the vortex. , …”