The electronic structure of Nb sub(3)Al/Nb sub(3)Sn, a new test case for flat/steep band model of superconductivity

In this work, we choose Nb sub(3)Al/Nb sub(3)Sn as a new test case for flat/steep band model of superconductivity. Based on the density functional theory in the generalized gradient approximation, the electronic structure of Nb sub(3)Al/Nb sub(3)Sn has been studied. The obtained results agree well with those of the earlier studies and show clearly flat bands around the Fermi level. The steep bands as characterized in this work locate around the M point in the first Brillouin zone. The obtained results reveal that Nb sub(3)Al/Nb sub(3)Sn fits more to the "Flat/steep" band model than to the van-Hove singularity scenario. The flat/steep band condition for superconductivity implies a different thermodynamic behavior of superconductors other than that predicted from the conventional BCS theory. This observation sets up an indicator for selecting a suitable superconductor when its large-scale industrial use is needed, for example, in superconducting maglev system or ITER project.