Normal-Superconducting Phase Transition Mimicked by Current Noise

Abstract

As a superconductor goes from the normal state into the superconducting state, the voltage vs. current characteristics at low currents change from linear to non-linear. We show theoretically and experimentally that the addition of current noise to non-linear voltage vs. current curves will create ohmic behavior. Ohmic response at low currents for temperatures below the critical temperature $T_c$ mimics the phase transition and leads to incorrect values for $T_c$ and the critical exponents $\nu$ and $z$. The ohmic response occurs at low currents, when the applied current $I_0$ is smaller than the width of the probability distribution ${\sigma }_I$, and will occur in both the zero-field transition and the vortex-glass transition. Our results indicate that the transition temperature and critical exponents extracted from the conventional scaling analysis are inaccurate if current noise is not filtered out. This is a possible explanation for the wide range of critical exponents found in the literature.

4 pages, 2 figures

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• Vortex glass-liquid transition and activated flux motion in an epitaxial, super-conducting NdFeAs(O,F) thin film
• Scaling analysis of the static and dynamic critical exponents in under, over, and optimally-doped Pr${}_{2-x}$Ce${}_x$CuO${}_{4-y}$ films
• Effects of Self-field and Low Magnetic Fields on the Normal-Superconducting Phase Transition
• Current-voltage characteristics and vortex dynamics in highly underdoped La${}_{2-x}$Sr${}_x$CuO${}_4$