Superconductivity through intra-atomic excitations
2009
Thursday 07 May 2009
from 15:15
to 16:15 at
Klein Auditorium
Speaker :
Peter Fulde (MPI for Complex Systems, Dresden)
Abstract :
Superconductivity occurs when the normal state of a metal becomes
instable due to Cooper pair formation. Usually it is assumed that the
glue for forming electron pairs is provided by phonons. For example,
the BCS theory is based on that assumption. After the discovery of
the high-temperature superconducting cuprates it was suggested that
other bosonic excitations rather than phonons should lead to Cooper
pairing. However, arguments have remained vague and a quantitative theory
is still lacking. On the other hand recent experiments on the filled
skutterudite PrOs4Sb12 have clearly demonstrated
that intra-atomic crystal field excitations of the 4f2
shell provide more than 50% to the binding energy of Cooper pairs. The
superconducting transition temperature is low in that case. Moreover,
in UPd2Al3 intra-atomic 5f excitations of the
U ions provide not only an explanation for Tc but also for
the observed magnetic resonance below Tc and for the heavy
quasiparticles found in that system. Phonons play only a negligible
role here.
Slides