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A strongly inhomogeneous superfluid in an iron-based superconductor
Among the mysteries surrounding unconventional, strongly correlated
superconductors is the possibility of spatial variations in their superfluid
density. We use atomic-resolution Josephson scanning tunneling microscopy to
reveal a strongly inhomogeneous superfluid in the iron-based superconductor
FeTe0.55Se0.45. By simultaneously measuring the topographic and electronic
properties, we find that this inhomogeneity in the superfluid density is not
caused by structural disorder or strong inter-pocket scattering, and does not
correlate with variations in Cooper pair-breaking gap. Instead, we see a clear
spatial correlation between superfluid density and quasiparticle strength,
putting the iron-based superconductors on equal footing with the cuprates and
demonstrating that locally, the quasiparticles are sharpest when the
superconductivity is strongest. When repeated at different temperatures, our
technique could further help elucidate what local and global mechanisms limit
the critical temperature in unconventional superconductors
Extremely Correlated Fermi Liquid Description of Normal State ARPES in Cuprates
The normal state single particle spectral function of the high temperature
superconducting cuprates, measured by the angle resolved photoelectron
spectroscopy (ARPES), has been considered both anomalous and crucial to
understand. Here we show that an unprecedentedly detailed description of the
data is provided by a spectral function arising from the Extremely Correlated
Fermi Liquid state of the t-J model proposed recently by Shastry. The
description encompasses both laser and conventional synchrotron ARPES data on
optimally doped BiSrCaCuO, and also conventional
synchrotron ARPES data on the LaSrCuO materials. {\em It
fits all data sets with the same physical parameter values}, satisfies the
particle sum rule and successfully addresses two widely discussed "kink"
anomalies in the dispersion.Comment: Published version, 5 figs; published 29 July (2011
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