Monday, July 25, 2011

Pseudogap does not twin with Superconducting gap: another evidence

I only have time to quickly graze over this interesting paper for the moment.
In underdoped cuprate superconductors, phase stiffness is low
and long-range superconducting order is destroyed readily by
thermally generated vortices (and anti-vortices), giving rise to
a broad temperature regime above the zero-resistive state in
which the superconducting phase is incoherent1–4. It has often
been suggested that these vortex-like excitations are related to
the normal-state pseudogap or some interaction between the
pseudogap state and the superconducting state5–10. However,
to elucidate the precise relationship between the pseudogap
and superconductivity, it is important to establish whether
this broad phase-fluctuation regime vanishes, along with the
pseudogap11, in the slightly overdoped region of the phase
diagram where the superfluid pair density and correlation
energy are both maximal12. Here we show, by tracking
the restoration of the normal-state magnetoresistance in
overdoped La2􀀀xSrxCuO4, that the phase-fluctuation regime
remains broad across the entire superconducting composition
range. The universal low phase stiffness is shown to be
correlated with a low superfluid density1, a characteristic of
both underdoped and overdoped cuprates12–14. The formation
of the pseudogap, by inference, is therefore both independent
of and distinct from superconductivity.

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