Alternative pseudogap scenario: Spectroscopic analogies between underdoped and disorderedBi2Sr2CaCu2O8+x

Disorder has a strong influence on the spectral properties of the ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+x}$ high-$T_c$ superconductor, both in the normal and in the superconducting state. High-resolution photoemission reveals a progressive quasiparticle suppression with increasing disorder in electron-irradiated optimally doped single crystals. The spectral line shapes of the disordered samples show striking analogies with those of underdoped samples specifically the widely discussed pseudogap at the chemical potential. Disorder provides therefore an alternative mechanism for spectral weight suppression near the Fermi surface, possibly coexisting and competing with other mechanisms. Since doping unavoidably introduces disorder, these results require a reconsideration of the relative importance of intrinsic effects vs disorder in high temperature superconductivity.