Abstract
Coupling between electrons and phonons (lattice vibrations) drives
the formation of the electron pairs responsible for conventional
superconductivity. The lack of direct evidence for electron–phonon
coupling in the electron dynamics of the high-transition-temperature
superconductors has driven an intensive search for an alternative
mechanism. A coupling of an electron with a phonon would result in
an abrupt change of its velocity and scattering rate near the phonon
energy. Here we use angle-resolved photoemission spectroscopy to
probe electron dynamics—velocity and scattering rate—for three different
families of copper oxide superconductors. We see in all of these
materials an abrupt change of electron velocity at 50–80 meV, which
we cannot explain by any known process other than to invoke coupling
with the phonons associated with the movement of the oxygen atoms.
This suggests that electron–phonon coupling strongly influences the
electron dynamics in the high-temperature superconductors, and must
therefore be included in any microscopic theory of superconductivity.
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