The absence of superconductivity in the next-to-leading order Ginzburg–Landau functional for Bardeen–Cooper–Schrieffer superconductor

Abstract

Shortly after the Gor’kov microscopic derivation of the Ginzburg–Landau (GL) model via a small order parameter expansion in Bardeen–Cooper–Schrieffer theory of superconductivity, the derivation was carried to next-to-leading order in that parameter and its spatial derivatives. The aim was to obtain a generalized GL free energy that approximates the microscopic model better. Since 1960s, multiple works have claimed or implicitly assumed that this extended GL model corresponds to the free energy and has solutions in the form of local minima describing superconductivity, such as vortex solutions. In contrast to this, we prove that this extended GL functional does not represent free energy since it does not have any solutions in the form of minima. Accordingly, it cannot be used to describe superconducting states.