Chapter 10 - Itinerant superconductivity

Abstract

This chapter focuses on the physical properties of the high-temperature superconductors. Superconducting strontium ruthenate (Sr2RuO4) discovered in 1994 has a similar structure as the cuprate La2−xBaxCuO4, which is the spin singlet d-wave superconductor, but Sr2RuO4 is the spin triplet p-wave or f-wave superconductor with a very low critical temperature. In superconducting cuprates and heavy-fermion materials discovered up to that time, there was coexistence or rather competition between the superconducting and antiferromagnetic phases. Such coexistence also takes place in borocarbide RM2B2C, discovered in 1994. The borocarbides are the first quaternary intermetallic systems that are superconducting. These materials are 3D in their behavior and thus, they are in fact quite different than the layered cuprates. It was established for all groups of superconductors that with the increase of critical temperature the isotope effect decreases. The isotope effect is a strong confirmation of the BCS theory in the case of classic superconductors. This effect is the change of the critical temperature with the isotope mass of the superconductor. In the case of superconducting cuprates, the isotope effect is caused by the mass change of vibrating oxygen atoms in the CuO2 plane. The O16 atoms can be replaced by O18.