Possible condensation of Cooper triples

Abstract

We theoretically discuss the possible condensation of Cooper triples, which correspond to a three-body version of Cooper pairs, in three-component Fermi systems with three-body attractive interactions. A macroscopic number of Cooper triples can occupy a zero center-of-mass momentum state in the presence of a Fermi surface of constituent particles, even though the three-body operator exhibits anti-commutation relation associated with the Fermi-Dirac statistics. Such a condensation with internal degrees of freedom is similar to bosonization in a system of infinite-component fermions. We propose a variational wave function for condensed Cooper triples and show that in the ground state, the condensed state is energetically favored compared to the normal state. Also, we discuss effects of the Fermi-surface distortion in a lattice system described by a three-component Hubbard model.