Abstract
A new low photon energy regime of angle-resolved photoemission spectroscopy
is accessed with lasers and used to study the high Tc superconductor
Bi2Sr2CaCu2O8+δ. The low energy increases bulk sensitivity, reduces
background, and improves resolution. With this we observe spectral
peaks which are sharp on the scale of their binding energy—the clearest
evidence yet for quasiparticles in the normal state. Crucial aspects
of the data such as the dispersion, superconducting gaps, and the
bosonic coupling kink are found to be robust to a possible breakdown
of the sudden approximation.
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