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Abstract:
We present a detailed study of the superconducting properties of the
weakly pinned, quasi-two-dimensional superconductor 2H-NbSe2, and its
intercalated variant NbSe2{CoCp2}(0.26). The intercalation of 2H-NbSe2
with the organometallic donor molecule cobaltocene (CoCp2) hardly
affects the superconducting properties within the layers. However, the
properties perpendicular to the layers change significantly due to the
large expansion of the layer spacings of the host lattice in the
c-direction by a factor of about two. In particular, the superconducting
anisotropy factor Gamma increases from 3.3 in the parent compound
2H-NbSe2 up to 4.4 in the intercalated species. Therefore,
NbSe2{CoCp2}(0.26) is an excellent candidate to analyze how the
anisotropy effects the superconducting mechanism in layered
dichalcogenides, and to evaluate the various models proposed in the
literature to account for the anisotropy in 2H-NbSe2. While a two-gap
model and an anisotropic single-gap model are competing concepts to
describe the almost linear T-2-dependence of Delta C/T in
low-dimensional dichalcogenides, our comparative study suggests that a
single-gap model with an anisotropic Fermi-surface is sufficient to
capture the Delta C/T (T) behavior in our samples qualitatively.
