No concensus

A glance at how fierce the quarrels over the working mechanism of high Tc superconductors are !

No one is predicting a full understanding of high-temperature superconductivity any time soon — not least because such an account would have to make sense of the huge number of papers. “A rich enough theory should explain everything and not just cherry pick,” says David Pines, a physicist from the University of Illinois at Urbana-Champaign.
But it’s not always clear exactly what needs to be explained. Roughly 15 years ago, for example, researchers discovered that some high-temperature superconductors allow electron pairs to form above the transition temperature. In this ‘pseudogap’ regime, the material
spontaneously organizes itself into stripes: linear regions that act like rivers and carry electron pairs through the insulating landscape where electrons remain stuck in place. “It’s a precursor state to the superconducting state and is therefore fundamental to understanding this problem,” says Ali Yazdani, a physicist at Princeton University. Not so, says Pines, who thinks the pseudogap state “interferes with superconductivity but is not responsible for it”.
Much as physicists had to wait for highly developed quantum-mechanical tools to unlock the secret behind traditional superconductivity, researchers today may require future ideas to complete their task.
If nothing else, the field’s early quarrels have ensured that only the most determined researchers have stayed. Those remaining are perhaps humbled by their experiences. “I think our biggest problem has been human fallibility,” says Anderson. And perhaps these initial difficulties have helped to forge theories that can stand the test of time. “In the end, it’s your competitor that makes you strong,” says Shen

Nesting not so holy in pnictides

This [Phys. Rev. B 83, 220504 (2011)] might be call theories solely based on nesting into question !

Despite intense study, researchers have not yet uncovered the secrets behind the peculiar properties of iron-based (pnictide) superconductors. Many theories that try to explain the driving mechanism of superconductivity in these materials suggest it is tied to so-called nesting of the electron and hole Fermi surfaces. This geometric feature of the Fermi surface, where one portion of the surface maps to another if it is translated by a suitable reciprocal-lattice vector, is common to the structure of many families of pnictides. Nesting often implies the existence of collective electron behavior, so if it is present in the host materials of the pnictides, it would have significant implications for their properties.

In a Rapid Communication appearing in Physical Review B, Brendan Arnold at the University of Bristol, UK, and colleagues use the de Haas-van Alphen effect, where electrons and holes orbit the extrema of the Fermi surface in response to a magnetic field, to map out the electron and hole Fermi surface sheets of BaFe₂P₂, the parent material of an important family of pnictide materials. Besides providing highly detailed information about the geometry of the Fermi surfaces, they find, rather surprisingly, that the nesting present in the superconducting doped compounds BaFe₂(As_1-xP_x)₂ persists in BaFe₂P₂, which is not superconducting. This finding agrees with a growing list of experiments that conclude nesting does not play a dominant role in the development of superconductivity, at least in one family of pnictide compounds. – Alex Klironomos

The current

I think I have missed some very funny things these days. I would like to pile their links below and I'll come back to them as I get time.
1. Physics, 4:26 (2011), by I.I.Mazin. This is a review on the puzzles and surprised conferred by the iron-based superconductors, which shows quasi-3D structure rather than a 2D one, quite different from their cuprate counter-parts.
2. Physics, 4:25 (2011), by P.Recher et al. This is an analog of spin Hall effect. It reviews a work that shows how a line defect could be utilized to filter valley-featured carriers in graphene.
3. Science, 331: 1579 (2011), by R.-H. He et al. This is a sequel to an earlier article by these authors. They have previously argued that, two gaps of distinct origins should exist in cuprates instead of one. Here they further explore their work and show the opening of the pseudogap might be related to a phase transition.