On the maximum reduced upper critical magnetic field in Eliashberg theory |
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Authors: | M Schossmann J P Carbotte E Schachinger |
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Affiliation: | (1) Physics Department, McMaster University, Hamilton, Ontario, Canada;(2) Institut für Theoretische Physik, Technische Universität Graz, Graz, Austria |
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Abstract: | Consideration of the functional derivative of the zero-temperature reduced upper critical magnetic fieldh
c2(0) with electron-phonon spectral density 2
F( ) suggests that its value can be maximized, for a given areaA under 2
F( ), with the choice of a delta-function spectral density. We show thath
c2(0) is then independent ofA and that it increases steadily as the Einstein frequency E of the delta function is lowered. We argue that there is a local maximum inh
c2(0) at E=0. The value at maximum is very sensitive to impurity content and increases sharply from a clean-limit value of 1.5 atT
c
/ E=1.33 to more than 3.45 in the dirty limit. |
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