Superconducting anisotropic

Nomura K, Muraoka R, Matsunaga N, Ichimura K, Yamada J (2009) Anisotropic superconductivity in j8-(BDA-TTP)2SbF6 STM spectroscopy. Physica B 404 562-564... 

Besides its anisotropic electrical and optical properties, this solid exhibits superconductivity at low temperatures. 

In anisotropic superconductivity one has to consider configuration interaction between pairs, in an energy window AE around the Fermi level, in different locations of the k-space with a different pairing strength, that gives a k-space dependent superfluid order parameter i.e., a k-dependent superconducting gap. 

A particular case of anisotropic superconductivity is multiband superconductivity, where the order parameter and the excitation gap are mainly different in different bands. 

The above picture is in a good agreement with the theory of itinerant electron systems with interplay between superconductivity and magnetism [8], In that theory, an itinerant SDW gap may appear at the Fermi surface only before an SC gap, i.e. in the normal state. This SDW gap is highly anisotropic since it is only formed at symmetric parts of the Fermi surface [8] ( see, fig.2). Its width ASDW being unusually large for an SC gap, well conforms to that for an SDW gap because of inequality ASc < ASDW... 

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