Ab initio calculation of a Pb single layer on a Si substrate: two-dimensionality and superconductivity

TL;DR

This study uses first principles calculations to explore superconductivity in a single lead layer on silicon, revealing a higher theoretical critical temperature than experiments, likely due to order parameter fluctuations.

Contribution

It provides a detailed ab initio analysis of 2D superconductivity in a Pb monolayer on Si, highlighting the failure of bulk approximations in 2D and suggesting fluctuation effects suppress Tc.

Findings

Calculated Tc is higher than experimental 1.86K.

Bulk approximations fail in 2D geometry.

Order parameter fluctuations likely suppress Tc.

Abstract

We report on first principles calculations of superconductivity in a single layer of lead on a silicon substrate including a full treatment of phononic and RPA screened coulomb interactions within the parameter free framework of Density Functional Theory for superconductors. A thorough investigation shows that several approximations that are commonly valid in bulk systems fail in this constrained 2D geometry. The calculated critical temperature turns out to be much higher than the experimental value of 1.86K. We argue that the only plausible explanation for the experimental Tc suppression is the onset of fluctuations of the superconducting order parameter.