Recent high-magnetic-field experiments on the “High Tc” cuprates; Fermi-surface instabilities as a driver for superconductivity

We give a brief review of high-magnetic-field quantum-oscillation measurements on cuprate superconductors. In the case of the underdoped cuprates, a number of small Fermi-surface pockets are observed, probably due to the incommensurate nesting of the predicted (large) hole Fermi surface. The Fermi-surface instabilities that drive this nesting are also likely to result in the incommensurate spin fluctuations observed in inelastic neutron-scattering measurements. We suggest that the unusually high superconducting transitions in the cuprates are driven by an exact mapping of these incommensurate spin fluctuations onto the dx2-y2 Cooper-pair wavefunction. The maximum energy of the fluctuations ∼100s of Kelvin gives an appropriate energy scale for the superconducting transition temperature.