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## Main Question or Discussion Point

**EM response function of the "Phase Action" of a BCS superconductor**

Hello,

I am looking for a paper in which people calculated the EM response of phase action of A BCS SC. In the book "Condensed Matter Field Theory" by Altland and Simons, on page 393 they mention such a thing in the discussion of divergence of conductivity.

I would appreciate it if you could introduce me some references, as my effort to find it through search for it has been futile.

Here is the action:

[tex] S[\theta]=\int dx ( \nu (\partial_\tau \theta)^2+\frac{n_s}{2m} (\nabla \theta)^2 )[/tex]

Here is what is needed to be calculated:

[tex] K_{ij}(x,x')=-\frac{n_s}{m}[\delta_{ij}-\frac{n_s}{m}\left\langle \partial_i \theta (x) \partial_j \theta(x') \right \rangle] [/tex]

Thank you in advance!