Bound states of Cooper's pairs and Electrons in the Superconducting Phase of $MgB_2$
Naoum Karchev
Sofia University
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The two-band theory of superconductivity of $MgB_2$ with
additional six-fermion interaction is considered. It is shown that a
bound state of a spin-singlet Cooper pair of fermions from one of
the bands and an individual fermion from the other one is possible.
The spin-1/2 triples with zero angular momentum are made up of three
spin-1/2 fermions with charge \emph{e}. They are gapped Fermi
excitations with gap induced by the gaps of the single fermions.
Their contribution to the thermodynamics of the $MgB_2$
superconductors is considered. The most promising way to observe the
triples in $MgB_2$ is by tunneling experiments.