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Excitation Gap in the Normal State of Underdoped Bi2Sr2CaCu2O8+delta
1A. G. Loeser, Z.-X. Shen, and C. H. Park are in the Department of Applied Physics, Stanford Synchrotron Radiation Laboratory, and Solid State Laboratory, Stanford University, Stanford, CA 94305, USA. D. S. Dessau is with the Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305, USA. D. S. Marshall is with the Solid State Laboratory, Stanford University, Stanford, CA 94305-4055, USA. P. Fournier and A. Kapitulnik are in the Department of Applied Physics, Stanford University, Stanford, CA 94305, USA.
Abstract:
Angle-resolved photoemission experiments reveal evidence of an energy gap in the normal state excitation spectrum of the cuprate superconductor Bi2Sr2CaCu2O8+delta. 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 dx2-y2 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.
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