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Strong-coupling d-wave superconductivity in PuCoGa_5 probed by point contact spectroscopy | | D. Daghero
; M. Tortello
; G.A. Ummarino
; J.-C. Griveau
; E. Colineau
; R. Eloirdi
; A. B. Shick
; J. Kolorenc
; A. I. Lichtenstein
; R. Caciuffo
; | | Date: |
2 Dec 2011 | | Abstract: | A century on from its discovery, a complete fundamental understanding of
superconductivity is still missing. Considerable research efforts are currently
devoted to elucidating mechanisms by which pairs of electrons can bind together
through the mediation of a boson field different than the one associated to the
vibrations of a crystal lattice. PuCoGa_5, a 5f-electron heavy-fermion
superconductor with a record critical temperature T_c=18.5 K, is one of the
many compounds for which the short-range, isotropic attraction provided by
simple electron-phonon coupling does not appear as an adequate glue for
electron pairing. Here, we report the results of point-contact spectroscopy
measurements in single crystals of PuCoGa_5. Andreev reflection structures are
clearly observed in the low-temperature spectra, and unambiguously prove that
the paired superconducting electrons have wavefunction with the d-wave symmetry
of a four-leaf clover. A straightforward analysis of the spectra provide the
amplitude of the gap and its temperature dependence, Delta(T). We obtain
Delta(T -> 0) = 5.1 pm 0.3 meV and a gap ratio, 2Delta/k_B T_c = 6.5 pm
0.3, indicating that the compound is in the regime of strong electron-boson
coupling. The gap value and its temperature dependence can be well reproduced
within the Eliashberg theory for superconductivity if the spectral function of
the mediating bosons has a spin-fluctuations-like shape, with a peak energy of
6.5 meV. Electronic structure calculations, combining the local density
approximation with an exact diagonalization of the Anderson impurity model,
provide a hint about the possible origin of the fluctuations. | | Source: | arXiv, 1112.0481 | | Services: | Forum | Review | PDF | Favorites | |
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