A new method for calculating the functional derivative delta T-c/delta alpha F-2(Omega): Application to MgB2
We present a new method for calculating the functional derivative of the superconducting transition temperature T-c with respect to the electron-phonon coupling function alpha(2)F(Omega). The method relies on a highly efficient procedure for finding the largest eigenvalue and the corresponding eigenvector of a Hermitian matrix. The convergence problems that arise in the calculation of deltaT(c)/deltaalpha(2)F(Omega) for systems with low T-c and a large-maximum phonon frequency Omega(max) using the method based on the pair-breaking parameter are eliminated. We apply the new method of calculating deltaT(c)/deltaalpha(2)F(Omega) to MgB2, to the prototype strong coupling superconductor Pb and to weak coupling (BCS) superconductor Al.
functional derivative superconductivity electron-phonon coupling