Insensitivity of the Superconducting Gap to Variations in the Critical Temperature of Zn-Substituted Bi2Sr2CaCu2O8+δ Superconductors

The phase diagram of the superconducting high-T-c cuprates is governed by two energy scales: T*, the temperature below which a gap is opened in the excitation spectrum, and T-c, the superconducting transition temperature. The way these two energy scales are reflected in the low-temperature energy gap is being intensively debated. Using Zn substitution and carefully controlled annealing we prepared a set of samples having the same T* but different T-c's, and measured their gap using angle-resolved photoemission spectroscopy (ARPES). We show that T-c is not related to the gap shape or size, but it controls the size of the coherence peak at the gap edge.