Pseudopotential approach to superconductivity in MgB2

Superconductivity in MgB2 has been re-examined in BCS-Eliashberg framework by employing Mc-Millan's Tc-equation and form factors of MgB2 computed from the form factors of component metals (Model-I). The empty core model pseudopotential due to Ashcroft and random phase approximation form of dielectric screening due to Gellmann and Brueckner are used in the present work. An excellent agreement between the present values and other theoretically computed values of Tc and with the relevant experimental data for MgB2 confirms the validity of the present approach. The explicit dependence of λ and Tc on the isotopic masses of Mg and B, as revealed from the present work, confirms the role of lattice vibrations in the superconducting behaviour of MgB2 and the high value of Tc in it may be attributed to the phonon mediated e-e interaction coupled with higher values of phonon frequencies due to light mass of B atoms. It has also been observed that the pseudo-atom model (Model-II) with appropriate choice of the potential parameter rc successfully explains high value of Tc and isotope effect in MgB2, confirming the prominent role played by electron-phonon interaction in the high-Tc superconductivity observed in MgB2. The isotope effect exponent α-values obtained from the two models are in complete agreement with each other and the present value α = 0.46 is also much closer to the BCS value of 0.5. Interaction strength N0V values obtained from the two models are also in perfect agreement with each other and the present value N0V = 0.48 suggests that MgB2 is a strong coupling superconductor. (author)