Study on the effect of shear strain on the critical temperature of MgB2 superconductors

Abstract

Enhancing the superconducting transition temperature (Tc) is crucial for expanding the practical applications of superconductors. As a binary superconductor with strong application potential, MgB2 has been widely studied under hydrostatic, uniaxial, and biaxial strain, whereas the effects of shear strain remain largely unexplored. In this work, we systematically investigate how shear strain regulates the superconducting properties of MgB2 using first-principles density functional theory and the McMillan–Allen–Dynes formula. We calculate the stress–strain response of MgB2 under shear along the (001)[110] and (001)[11¯0] directions, together with the corresponding changes in Tc, electronic structure, phonon dispersion, and electron–phonon coupling. The calculated Tc of unstrained MgB2 is 38 K, in good agreement with the experimental value of 39 K. Under shear in the (001)[110] direction, Tc first decreases at a strain of 0.02, then increases monotonically, reaching 42 K at a strain of 0.16. Under shear in the (001)[11¯0] direction, Tc also decreases first and then increases, with a minimum of 36 K at a strain of 0.08 and a maximum of 42 K at a strain of 0.20. The Tc enhancement mainly arises from the combined effect of significant softening of strain-induced low-frequency phonons, especially the E1u and acoustic branches, and electronic-structure renormalization, including changes in the density of states near the Fermi level, which together strengthen electron–phonon coupling. This work provides guidance for understanding shear-strain effects in layered superconductors such as MgB2 and suggests new theoretical routes for optimizing Tc in layered superconducting materials.