Abstract
A recent highlight in the study of high-Tc superconductors is the
observation of band renormalization or self-energy effects on the
quasiparticles. This is seen in the form of kinks in the quasiparticle
dispersions as measured by photoemission and interpreted as signatures
of collective bosonic modes coupling to the electrons. Here we compare
for the first time the self-energies in an optimally doped and strongly
overdoped, nonsuperconducting single-layer Bi-cuprate (Bi2Sr2CuO6).
In addition to the appearance of a strong overall weakening, we also
find that the weight of the self-energy in the overdoped system shifts
to higher energies. We present evidence that this is related to a
change in the coupling to c-axis phonons due to the rapid change
of the c-axis screening in this doping range.
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