Biaxial strain engineering on the superconducting properties of MgB2 thin film

TL;DR

This study uses first-principles calculations to show that biaxial strain can effectively tune the superconducting critical temperature of MgB2 thin films, revealing mechanisms behind strain effects and guiding substrate selection.

Contribution

It provides a detailed microscopic understanding of how biaxial strain influences MgB2's superconductivity and demonstrates strain engineering as a viable method to enhance superconducting properties.

Findings

Tensile biaxial strain increases Tc of MgB2.

Compressive strain decreases Tc of MgB2.

Most substrates induce tensile strain consistent with experimental observations.

Abstract

The effect of biaxial strain on the superconducting properties of MgB2 thin films was studied by first-principles calculations. The stability analyses by phonon dispersions show that biaxial strain as much as 7% can be applied onto MgB2 without inducing any imaginary frequency. The superconducting property calculations based on the frame of Migdal-Eliashberg theory successfully reproduce the two-gap superconductivity of MgB2. The results show that the tensile biaxial strain can increase the critical temperature of MgB2 while the compressive biaxial strain would decrease the critical temperature. The detailed microscopic mechanism of the biaxial strain effect on the superconducting properties was studied by calculations of electronic structures and phonon dispersions. The increased Tc is a combining result of the increased electron density at the Fermi level and the in-plane boron phonon softening. By means of high-throughput screening of proper substrates, it is found that most of the substrates would result in tensile strain in MgB2 film, which is in agreement with many experimental works. The results in this work provide detailed understanding of the biaxial strain engineering mechanism and demonstrate that biaxial strain engineering can be an effective way of tuning the superconducting properties of MgB2 and other similar materials.