Normal-Superconducting Phase Transition Mimicked by Current Noise

TL;DR

This paper demonstrates that current noise can mimic a normal-superconducting phase transition, leading to incorrect determination of critical parameters if not properly filtered, affecting interpretations of experimental data.

Contribution

It provides both theoretical and experimental evidence that current noise induces ohmic behavior, which can be mistaken for a phase transition in superconductors.

Findings

Current noise causes ohmic response at low currents.

This response mimics the phase transition, affecting critical parameter estimation.

Filtering noise is essential for accurate critical exponent determination.

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.