Enhancement of superconductivity by a parallel magnetic field in two-dimensional superconductors

Jeffrey Gardner, H.; Kumar, Ashwani; Yu, Liuqi; Xiong, Peng; Warusawithana, Maitri P.; Wang, Luyang; Vafek, Oskar; Schlom, Darrell G.
November 2011
Nature Physics;Nov2011, Vol. 7 Issue 11, p895
Academic Journal
Superconductivity is a quantum state of matter characterized by the formation of Cooper pairs from time-reversal-symmetric electronic states. Mechanisms that break this symmetry, such as magnetic-impurity scattering and applied magnetic fields, are expected to be detrimental to superconductivity and suppress the critical temperature. Here, we report the observation of pronounced increases in the mean-field critical temperature on application of a parallel magnetic field in two different two-dimensional superconducting systems: ultrathin, homogeneously disordered amorphous Pb films and the two-dimensional electron gas at the interface of LaAlO3 and SrTiO3. In the amorphous Pb films, the critical-temperature increases exhibit a systematic dependence on the film thickness. Significantly, the presence of paramagnetic impurities in the films diminishes the effect of field enhancement of superconductivity. These observations mark a radical departure from the current understanding of the interactions between magnetic fields and superconductivity.


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