Abstract
A method is presented for the derivation of the quasiclassical equations for the Keldysh Green's function of a superconductor or superfluid3He. It is shown that the Green's functions on the classical trajectoriesĝ(y 1,y 2), which depend on two trajectory coordinatesy 1 andy 2, give the full description of the system within quasiclassical accuracy. The equation of motion forĝ(y 1,y 2) is obtained. It is shown thatĝ(y)=ĝ(y+0,y)+ĝ(y−0,y) is equal to the Green's function in momentum space integrated with respect to ξ=v F(p−p F). The normalization condition\([\hat g(y)]^2 = \hat 1\) is proved in a direct manner using the properties ofĝ(y 1,y 2) withy 1 ≠y 2. The different methods of introducing the distribution function are discussed.
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Shelankov, A.L. On the derivation of quasiclassical equations for superconductors. J Low Temp Phys 60, 29–44 (1985). https://doi.org/10.1007/BF00681651
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DOI: https://doi.org/10.1007/BF00681651