An explanation for a universality of transition temperatures in families of copper oxide superconductors

• Published in: Nature (London) 2004-03, Vol.428 (6978), p.53-55
• Main Authors: Chakravarty, Sudip, Kee, Hae-Young, Völker, Klaus
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Copper; Cuprates superconductors (high tc and insulating parent compounds); Effects of material synthesis, crystal structure, and chemical composition; Exact sciences and technology; High-Tc compounds; Humanities and Social Sciences; letter; multidisciplinary; Oxidation; Physics; Science; Science (multidisciplinary); Superconductivity; Superconductors; Temperature; Transition temperature variations; Transition temperatures
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature02348

A remarkable mystery of the copper oxide high-transition-temperature ( T c ) superconductors is the dependence of T c on the number of CuO 2 layers, n , in the unit cell of a crystal. In a given family of these superconductors, T c rises with the number of layers, reaching a peak at n = 3, and then declines 1 : the result is a bell-shaped curve. Despite the ubiquity of this phenomenon, it is still poorly understood and attention has instead been mainly focused on the properties of a single CuO 2 plane. Here we show that the quantum tunnelling of Cooper pairs between the layers 2 simply and naturally explains the experimental results, when combined with the recently quantified charge imbalance of the layers 3 and the latest notion of a competing order 4 , 5 , 6 , 7 , 8 , 9 nucleated by this charge imbalance that suppresses superconductivity. We calculate the bell-shaped curve and show that, if materials can be engineered so as to minimize the charge imbalance as n increases, T c can be raised further.