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Imaging the granular structure of high-Tc superconductivity in underdoped Bi2Sr2CaCu2O8+x

K. M. Lang·V. Madhavan·J. E. Hoffman·E. W. Hudson·H. Eisaki·S. Uchida·J. C. Davis
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Abstract

Granular superconductivity occurs when microscopic superconducting grains are separated by non-superconducting regions through which they communicate by Josephson tunneling to establish the macroscopic superconducting state [1]. Although crystals of the cuprate high-Tc superconductors are not granular in a structural sense, theory indicates that at low hole densities the holes can become concentrated at some locations resulting in hole-rich superconducting domains [2-5]. Granular superconductivity due to Josephson tunneling through 'undoped' regions between such domains would represent a new paradigm for the underdoped cuprates. Here we report studies of the spatial interrelationships between STM tunneling spectra in underdoped Bi2Sr2CaCu2O8+x. They reveal an apparent spatial segregation of the electronic structure into ~3nm diameter domains (with superconducting characteristics and local energy gap delta<50 meV) in an electronically distinct background. To explore whether this represents nanoscale segregation of two distinct electronic phases, we employ scattering-resonances at Ni impurity atoms [6] as 'markers' for the local existence of superconductivity [7-9]. No Ni-resonances are detected in any regions where delta>50(2.5) meV. These observations suggest that underdoped Bi2Sr2CaCu2O8+x is a mixture of two different short-range electronic orders with the long-range characteristics of a granular superconductor.

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K. M. Lang, V. Madhavan, J. E. Hoffman, E. W. Hudson, H. Eisaki, S. Uchida, J. C. Davis. 2001-12-12. Imaging the granular structure of high-Tc superconductivity in underdoped Bi2Sr2CaCu2O8+x. https://doi.org/10.1038/415412a

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