In this paper we study the multisheet superconducting system with intersheet and intrasheet pairing. In the mean-field approximation we derive and solve the coupled equations for the intersheet-pair and intrasheet-pair order parameters. We find that the order parameters are sensitive to both the intersheet and intrasheet coupling constants, however small or large the coupling constants may be. We define a characteristic parameter c which is a function of both coupling constants and is effectively useful in classifying the behavior of order parameters. To show a variety of temperature dependence, we present curves of order parameters versus temperature with different values of c. We see from these results that the intersheet pairs play a key role in maintaining the superconductivity. This suggests to us a significant aspect of lower-dimensional structure summarized by the term ‘‘pair multiplicity.’’ We show also some exotic behavior of the specific heat. In cases of low-dimensional structure, the reliability of the mean-field approximation is in question. We analyze this question.

• Received 11 December 1990

DOI:https://doi.org/10.1103/PhysRevB.44.351