Relationship between combinative energy and superconductivity in Tl 2Ba 2Ca n−1 Cu nO 2 n+4

Abstract

The non-monotonic relationship of T c with the number of Cu–O planes ( n) per unit cell for compounds of Tl 2Ba 2Ca n−1 Cu n O 2 n+4 ( n=1, 2, 3, and 4) is investigated from the perspective of cohesive energy. The unit cell of the Tl superconductors is treated as two blocks: the perovskite block where the Cu–O planes are located and the rock salt block, which is considered as a charge-reservoir. We proposed a model to calculate the combinative energy of the two blocks. It is found that the combinative energy between the two blocks is closely related to the value of T c. The relation demonstrates an interesting way to understand the nonlinear change of T c with the number of Cu–O planes in the layered superconductors. This means that the interaction between the two blocks plays an important role in superconductivity.