Basic aspects and main results of NMR-NQR spectroscopies in high-temperature superconductors

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Abstract
After a mention of the structural, magnetic and electronic properties of high-temperature superconductors (HTSC), the basic principles of NMR-NQR experiments in these compounds are presented, emphasizing the marked differences and the novel aspects of the latter systems in comparison with metals and conventional superconductors. It follows a review of NMR-NQR spectra and relaxation rates in two-dimensional quantum antiferromagnets (particularly ) driven towards the superconducting state by charge doping. The main results obtained in the normal state of HTSC are summarized, while the problems of the spin-gap and of the superconducting fluctuations are discussed to a certain extent, by including the most recent contributions. An overview is given on the main conclusions derived from NMR-NQR experiments in the superconducting state. A section is devoted to the insights into the vortex lattice and the flux lines motion that have been obtained from NMR line narrowing, and echo dephasing. This review deals mostly with three systems, , and .