Research Articles

Excitation Gap in the Normal State of Underdoped Bi2Sr2CaCu2O8+δ

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Science  19 Jul 1996:
Vol. 273, Issue 5273, pp. 325-329
DOI: 10.1126/science.273.5273.325


Angle-resolved photoemission experiments reveal evidence of an energy gap in the normal state excitation spectrum of the cuprate superconductor Bi2Sr2CaCu2O8+δ. This gap exists only in underdoped samples and closes around the doping level at which the superconducting transition temperature Tc is a maximum. The momentum dependence and magnitude of the gap closely resemble those of the dx2y2 gap observed in the superconducting state. This observation is consistent with results from several other experimental techniques, which also indicate the presence of a gap in the normal state. Some possible theoretical explanations for this effect are reviewed.