On details of the thermodynamical derivation of the Ginsburg–Landau equations

We examine the procedure of thermodynamical derivation of the Ginsburg–Landau equation for current, which is given unclear and contradictory interpretations in existing textbooks. We clarify all steps of this procedure and find as a consequence a limitation on the validity range of the thermodynamic Ginsburg–Landau theory, which does not seem to be explicitely stated up to now: we conclude that the thermodynamic theory is applicable only to a superconducting specimen that is not a part of an external current-carrying loop. PACS 74.20.De;