Tunneling spectroscopy of c-axis epitaxial cuprate junctions
arXiv:2001.03245 · doi:10.1103/PhysRevB.101.224512
Abstract
Atomically precise epitaxial structures are unique systems for tunneling spectroscopy that minimize extrinsic effects of disorder. We present a systematic tunneling spectroscopy study, over a broad doping, temperature, and bias range, in epitaxial c-axis LaSrCuO/LaCuO/LaSrCuO heterostructures. The behavior of these superconductor/insulator/superconductor (SIS) devices is unusual. Down to 20 mK there is complete suppression of c-axis Josephson critical current with a barrier of only 2 nm of LaCuO, and the zero-bias conductance remains at 20-30% of the normal-state conductance, implying a substantial population of in-gap states. Tunneling spectra show greatly suppressed coherence peaks. As the temperature is raised, the superconducting gap fills in rather than closing at . For all doping levels, the spectra show an inelastic tunneling feature at 80 meV, suppressed as exceeds . These nominally simple epitaxial cuprate junctions deviate markedly from expectations based on the standard Bardeen-Cooper-Schrieffer (BCS) theory.
arXiv comment12 pages, 4 figures
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