Superconductivity in repulsive electron systems having three-dimensional disconnected Fermi surfaces

TL;DR

This paper extends the concept of enhancing superconductivity via disconnected Fermi surfaces from 2D to 3D systems, demonstrating that certain 3D structures can achieve high critical temperatures through spin-fluctuation mechanisms.

Contribution

It introduces a 3D extension of the disconnected Fermi surface superconductivity concept and shows that specific 3D lattice structures can attain high Tc values similar to 2D cases.

Findings

Tc can reach approximately 0.01t in 3D structures

Superconductivity is optimized when the system is quasi-low dimensional

A properly

Abstract

The idea of raising Tc in the spin-fluctuation mediated superconductivity on disconnected Fermi surfaces with the gap function changing sign across but not within the Fermi pockets, proposed by Kuroki and Arita for two dimensions (2D), is here extended to three-dimensional (3D) systems. Two typical cases of 3D disconnected Fermi surfaces (stacked bond-alternating lattice and stacked ladder layers) are considered. By solving Eliashberg's equation for Green's function obtained with the fluctuation exchange approximation (FLEX) for the repulsive Hubbard model on these structures, we have shown that Tc can indeed reach O(0.01t), which is almost an order of magnitude higher than in ordinary 3D cases and similar to those for the best case found in 2D. The key factor found here for the favorable condition for the superconductivity on disconnected Fermi surfaces is that the system should be quasi-low dimensional, and the peak in the spin susceptibility should be appropriately "blurred".