Study on the most effective pressure application method to increase the critical temperature of MgB2

Abstract

Previous studies have shown that the critical transition temperature (TC) of MgB2 increases with the a-axis plane stretching, but decreases under hydrostatic pressure, indicating that different pressure application methods have different effects on the TC of MgB2. In order to further find out the most effective pressure application method that can improve the TC of MgB2, based on the McMillan superconducting calculation formula and the first-principles density functional theory, this paper studies the TC change of MgB2 under the crystal axis strain by constructing the fitting formula between the crystal axis strain and the change of the electron-phonon coupling constant λ and TC of MgB2. In addition, the TC changes under hydrostatic pressure, a-axis plane pressure and c-axis unidirectional pressure are analyzed and compared by using the constructed fitting formula. The results show that the pressure application method of a-axis plane stretching is more efficient for improving TC. According to the change trend of TC under crystal axis strain, a most efficient pressure application method to increase TC of MgB2 was proposed: apply an appropriate pressure in the c-axis direction while applying tensile force in the a-axis plane. The research in this paper has certain theoretical and guiding significance for improving the TC of MgB2 by applying pressure and understanding the superconducting mechanism of MgB2 materials.