Physics Today: Fe-based Superconductors, first dedicated synchrotron facility

May-2008 issue of Physics Today has an article on recently discovered Fe-based superconductors.

In the same issue there’s an article on evolution of a dedicated synchrotron facility, a 240 MeV storage ring in Winsconsin named Tantalus.

Superconductivity in iron-based layered compounds

The featured article this time is advanced online publication in Nature on Superconductivity in FeAs-based layered compounds by Takahashi et al.

This is the first publication in Science/Nature from what I am sure many to follow on this topic, with a few new publications per day appearing on arxiv.

By starting with LaOFeAs compound and doping F at oxygen sites, the

superconducting temperature of 26K is reached under atmospheric pressure. This Tc can be increased up to 43K by applying pressure (maximum of 43K at

4GPa, with the higher pressure decreasing the Tc). This is the highest

non-cuprate Tc observed, and there is already some evidence that the pairing mechanism is non-conventional.

Ode to crystal growers

Deviating from our usual theme of centering attention on research manuscripts, here’s an excellent article in August’07 issue of Physics Today, on US condensed-matter community grapples with availability of crystalline samples.

Abstract:

Crystal growing for physics measurements has fallen between the cracks in the US; without a turnaround, the country can’t help but lag in the discovery of new materials and their applications.

August 2007, page 26

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 arxiv.org 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.

Seamus Davis on “Atomic Scale Visualization of ‘Pseudogap’ Electronic Matter in Cuprates”

Kavli Institute on Theoretical Physics at Santa Barbara, KITP, has a great program of posting videos and slides of their numerous talks online. (You can also subscribe to their numerous RSS feeds and get them as podcasts)

This week I listened to an excellent talk by Seamus Davis of Cornell on Atomic Scale Visualization of ‘Pseudogap’ Electronic Matter in Cuprates .

This talk was a part of an on-going symposium on strongly correlated systems and cold atoms. There was also another talk by Davis a few days before, providing a nice introduction to STS and d-wave superconductivity.