3 research outputs found
Electron-phonon interaction in C70
The matrix elements of the deformation potential of C are calculated
by means of a simple, yet accurate solution of the electron-phonon coupling
problem in fullerenes, based on a parametrization of the ground state
electronic density of the system in terms of hybridized orbitals.
The value of the calculated dimensionless total electron-phonon coupling
constant is , an order of magnitude smaller than in
C, consistent with the lack of a superconducting phase transition in
CA fullerite, and in overall agreement with measurements of the
broadening of Raman peaks in CK. We also calculate the photoemission
cross section of C, which is found to display less structure than that
associated with C, in overall agreement with the experimental
findings.Comment: To be published in Phys. Rev.
Influence of internal disorder on the superconducting state in the organic layered superconductor kappa-(BEDT-TTF)2Cu[N(CN)2]Br
We report high-sensitivity AC susceptibility measurements of the penetration
depth in the Meissner state of the layered organic superconductor
kappa-(BEDT-TTF)2Cu[N(CN)2]Br. We have studied nominally pure single crystals
from the two different syntheses and employed controlled cooling procedures in
order to minimize intrinsic remnant disorder at low temperatures associated
with the glass transition, caused by ordering of the ethylene moieties in
BEDT-TTF molecule at T_G = 75 K. We find that the optimal cooling procedures
(slow cooling of -0.2 K/h or annealing for 3 days in the region of T_G) needed
to establish the ground state, depend critically on the sample origin
indicating different relaxation times of terminal ethylene groups. We show
that, in the ground state, the behavior observed for nominally pure single
crystals from both syntheses is consistent with unconventional d-wave order
parameter. The in-plane penetration depth lambda_in(T) is strongly linear,
whereas the out-of-plane component lambda_out(T) varies as T^2. In contrast,
the behavior of single crystals with long relaxation times observed after slow
(-0.2 K/h) cooling is as expected for a d-wave superconductor with impurities
(i.e. lambda_in(T) propto lambda_out(T) propto T^2) or might be also reasonably
well described by the s-wave model. Our results might reconcile the
contradictory findings previously reported by different authors.Comment: 13 pages, 10 figures, submitted to Phys. Rev.