Search for Fermi surface, inhomogeneous gaps and sliding CDWs

In this week’s Nature there are two papers on high-Tc superconductors:

Doiron-Leyraud et al. observe a Fermi surface signature in extremely pure underdoped YBCO samples – the Fermi surface area is small, pointing to a possibility of small enclosed pockets, perhaps related to small Fermi arcs detected previously by ARPES measurements.

There is also a nice News and Views item by Steve Julian and Mike Norman.

Another paper in the same issue on similar subject of high-Tc is work by Ali Yazdani’s group (Gomez et al.) looking at spatially inhomogeneous distribution of superconducting

gap in BSCCO. Gap varies spatially over 1-3 nm, but Tc is well correlated with the local value of the gap. It’s a nice work using extremely stable STS measurements, similar to the work done by Seamus Davis group, discussed here a few weeks ago.

Finally, a new paper on by Los-Alamos’ Magnet Lab John Singleton & Al Migliori ‘s group working in collaboration with Peter Littlewood reports observations of collective dynamics (sliding) of CDW condensate in LCMO (Susan Cox et. al). The broadband noise and hysteretic resistivity indicates of collective sliding of CDW, which is a classic example of non-linear transport properties due to interactions of charge-ordered condensate with random pinning centers. This is similar to classic examples of NbSe3, TbS3 as well as various organic quasi-1D compounds, but manganites tend to be more disordered and therefore pinning effects are more enhanced.

Somewhat related to CDW topic is a recently attended talk at IPNS by Nancy Ru from Ian Fischer’s group at Stanford, who discussed role of chemical pressure (a term some folks find rather misleading) in bi-layer splitting of Fermi surface in rare earth tellurides which drives the CDW transition temperature down in a rather dramatic fashion.

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