Extremely strong coupling superconductivity in artificial two-dimensional Kondo lattices

Nature Physics (Impact Factor: 19.35). 09/2011; 7(11). DOI: 10.1038/nphys2112
Source: arXiv

ABSTRACT When interacting electrons are confined to low-dimensions, the
electron-electron correlation effect is enhanced dramatically, which often
drives the system into exhibiting behaviors that are otherwise highly
improbable. Superconductivity with the strongest electron correlations is
achieved in heavy-fermion compounds, which contain a dense lattice of localized
magnetic moments interacting with a sea of conduction electrons to form a 3D
Kondo lattice. It had remained an unanswered question whether superconductivity
would persist upon effectively reducing the dimensionality of these materials
from three to two. Here we report on the observation of superconductivity in
such an ultimately strongly-correlated system of heavy electrons confined
within a 2D square-lattice of Ce-atoms (2D Kondo lattice), which was realized
by fabricating epitaxial superlattices built of alternating layers of
heavy-fermion CeCoIn5 and conventional metal YbCoIn5. The field-temperature
phase diagram of the superlattices exhibits highly unusual behaviors, including
a striking enhancement of the upper critical field relative to the transition
temperature. This implies that the force holding together the superconducting
electron-pairs takes on an extremely strong coupled nature as a result of

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