Towards an effective mass model for the quasi-1D magnesium diboride superconducting nanostructures

Abstract

We developed a parabolic effective mass model with the aim to describe the in-plane constricted superconductivity in few-monolayer MgB$_2$. The model was employed to study a constricted quasi-$1$D superlattice with the simplest version of the Anderson approximation. Resonant Fano-Feshbach-like effect was found, between a miniband of a continuous normal state dispersion cutting across $E_F$ and a miniband of quasi-discrete dispersion, even though the latter is significantly energetically distanced from the Fermi level. The origin of the phenomenon was identified to be the presence of characteristic strongly localised eigenstates, due to the specific material parameters. Moreover, the mechanism leading to a "precursor" pseudogap region in a system with a non-zero phase difference is described, when the strength of the coupling is still not sufficient to open a superconducting gap, but enough to introduce electron-hole mixing into the system.