High-77 cuprates superconductivity mechanism

More than 15 years after the discovery of high-Tc superconductivity in layered cuprates its mechanism is still under debate. This has to do with the asymmetry of physical properties between the electron-doped and hole-doped side of the complex phase diagram, temperature vs. doping, T(x), and with the fact that no consensus has been reached about the question what are the key experiments a theory of high-Tc superconductivity must be able to explain. In this paper we argue that the elementary excitations and their interdependence with spin excitations in the cuprates are of central interest in order to learn more about the correlations in general and, in particular, about the mechanism for Cooper-pairing in these systems. 

High temperature superconductivity in cuprates occurs upon hole doping in half-filled antiferromagnetic insulating parent compounds. More than 20 years has passed since the discovery of the high temperature superconductivity in cuprates [1], Despite very extensive and intensive researches, the mechanism for it is still not elucidated. 

There is little question that the physics and chemistry of the high-Tc cuprates have been among the preeminent research topics in condensed-matter physics during the past decade. Much of the initial experimental and theoretical investigation of these materials was aimed at clarifying the mechanism responsible for high-Tc superconductivity. Yet, as the... 

There is no consensus on the mechanisms of high T superconductivity in doped cuprates. There is also no generally accepted assignment of the spectrum of pure as well as doped cuprates. Convincing experimental evidence shows, however, that the doping sites, consisting of Cu + ions, are local. 

Cox and Maple 1995, Levi 1993, 1996). The pairing synunetry provides clues to the identity of the superconducting pairing mechanism which is essential for the development of the theory of high-temperature superconductivity in the cuprates. 

Since it is apparent that the high temperature superconductivity of cuprates cannot be explained by the Bardeen-Cooper-Schrieffer (BCS) mechanism that explained the low temperature superconductors so beautifully, the role of the... 

Until the discovery of high-temperature superconductivity of cuprates by Bednorz and Muller in 1986 [2] and synthesis of first 90 K superconductor [3] in 1987, understanding of microscopic mechanism of superconducting (SC) state transition formulated within the BCS theory in 1957 [4] was generally accepted as a firm theoretical basis behind the physics of this phenomenon. The idea of Cooper-pair formation, i.e. formation of boson-like particles in momentum space, which are stable in a thin layer above the Fermi level and drive the system into more stable - superconducting state, is crucial in this case. Sufficient condition of pair formation is a weak, but attractive interaction between electrons. The possibility of effective attractive electron-electron (e-e) interactions was derived by Frdhlich [5,6] as a consequence of electron-phonon (e-p) interactions. 

In the meantime some new routes towards high temperature and possibly exotic superconductivity have been investigated. This is the case for the heavy fermion compounds in which the close interplay between local magnetic moments and the spin of delocalized electrons has led to the possibility of a nonphonon mediated mechanism for electron pairing [4]. A very successful route towards high-T, s has been followed with conducting layered cuprates after the discovery of superconductivity in (La, Sr)2Cu04 [5]. 

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