Pnictides: They’re not cuprates…

People have recently been pondering over the symmetry of the order parameter in the newly discovered (iron-based) pnictide superconductors. Being layered materials, like the cuprates, it was thought that they might be d-wave. However, there is some theoretical basis to them being s-wave, see here and here (Parental Advisory: contains explicit band structure calculations).

Well, here’s the usual experimental way of settling this matter:

Phase-Sensitive measurements on the corner junction of iron-based superconductor BaFe1.8Co0.2As2.

I thought that this might be done soon. See here and here for some early examples of this (rather beautiful) experiment involving YBCO.

cornerjuncts
(Picture © Van Harlingen 1995)

The basis of the method involves making a tunnel junction using a ‘corner’ of a piece of the superconductor of interest. The corner encompasses tunnel directions along both the a and b crystal axes. The other side of the junction is a superconductor which is known to have a direction-independent order parameter symmetry, such as Pb. If the order parameter changes phase with respect to crystal direction, there is a built in phase shift across the junction, which manifests as a shift in the Fraunhofer-type diffraction pattern of the critical current with respect to applied field.

They conclude that the superconductor is probably s-wave (or at least MOSTLY s-wave). No more yummy pi-junction candidates yet then.

I love the last line of the paper:

“This indicates that the superconducting wavefunction of
the iron based superconductor is definitely not like that of a
cuprate superconductor.”

[EDIT 19/12/08] Here is another related paper

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One thought on “Pnictides: They’re not cuprates…

  1. rrtucci says:

    Does your mom read this blog? Neap tides; they’re not curates. What does she think about her daughter’s intelligence?

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