Band structure of MgB2 with different lattice constants

We report a detailed study of the electronic structure of the MgB₂ with different lattice constants by using the full-potential linearized augmented plane-wave method. It is found that the lattice parameters have great effect on the σ band of boron. Our results indicate that increasing the lattice constant along the c axis will increase the density of states at the Fermi level, shift the σ band upward, and increase the hole number in the σ band. So, the superconducting transition temperature T_c will be raised correspondingly. Changing the lattice constant along a axis has the opposite effect to that of the c axis. Our result is in agreement with the experiment. A possible way of searching for higher T_c superconductor has been indicated, i.e., making MgB₂ to have longer c axis and shorter a,b axis by doping.