Relationship between the superconducting energy gap and the critical temperature in high-Tc superconductors

The relationship between the superconducting energy gap and the critical temperature T-c in high-T-c superconductors is discussed. By examining carefully some of the most recent low temperature data of penetration depth, angle resolved photoemission, and tunneling spectroscopy measurements, we conclude that the gap amplitude at the d-wave nodes scales with T-c. This scaling behavior holds independent of carrier concentration although in the underdoped regime the maximum gap does not scale with T-c.