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Cooper Triples in Attractive SU(3) Fermions with an Asymptotic Freedom

Hiroyuki Tajima, Shoichiro Tsutsui, Takahiro M. Doi, Kei Iida

Published Dec 7, 2020• 1 citation
OpenAlex

Abstract

We investigate many-body properties of equally populated three-component fermions with attractive three-body contact interaction. A diagrammatic approach suggests the possible occurrence of Cooper triples at low temperature, which are a three-body counterpart of Cooper pairs with a two-body attraction. In one-dimension, the presence of Cooper triples is accompanied by conformal symmetry breaking, which is in turn related to an asymptotic freedom of the low-dimensional, multi-component system. While trimer states present at sufficiently low density have the binding energy reduced by the Pauli blocking and the thermal agitation, Cooper triples are predicted to take over for the even larger Fermi surface. We develop a minimal framework that bridges such a crossover from tightly-bound trimers to Cooper triples with increasing particle number density.

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We investigate many-body properties of equally populated three-component fermions with attractive three-body contact interaction. A diagrammatic approach suggests the possible occurrence of Cooper triples at low temperature, which are a three-body counterpart of Cooper pairs with a two-body attraction. In one-dimension, the presence of Cooper triples is accompanied by conformal symmetry breaking, which is in turn related to an asymptotic freedom of the low-dimensional, multi-component system. While trimer states present at sufficiently low density have the binding energy reduced by the Pauli blocking and the thermal agitation, Cooper triples are predicted to take over for the even larger Fermi surface. We develop a minimal framework that bridges such a crossover from tightly-bound trimers to Cooper triples with increasing particle number density.
We investigate many-body properties of equally populated three-component fermions with attractive threebody contact interaction in one dimension.A diagrammatic approach suggests the possible occurrence of Cooper triples at low temperature, which are three-body counterparts of Cooper pairs with a two-body attraction.We develop a minimal framework that bridges the crossover from tightly bound trimers to Cooper triples with increasing chemical potential and show how the formation of Cooper triples occurs in the grand-canonical phase diagram.Moreover, we argue that this nontrivial crossover is similar to the hadron-quark crossover proposed in dense matter.A coexistence of medium-induced triples and the underlying Fermi sea at positive chemical potential is analogous to quarkyonic matter consisting of baryonic excitations and the underlying quark Fermi sea.The comparison with the existing quantum Monte Carlo results implies that the emergence of these kinds of three-body states can be a microscopic origin of the peak of the sound velocity along the crossover.
The condensation of Cooper pairs, originating from the Fermi-surface instability due to a weakly attractive interaction between two fermions, opened a new frontier for exploring many-body physics in interdisciplinary contexts. In this work, we discuss the possible condensation of Cooper triples, which are three-body counterparts of Cooper pairs for three-component fermions with a three-body attraction. Although each composite trimer-like state obeys the Fermi-Dirac statistics, its aggregate can form a condensate at zero center-of-mass momentum in the presence of the internal degrees of freedom associated with the relative momenta of constituent particles of momenta close to the Fermi surface. Such condensation can be regarded as bosonization in infinite-component fermions. We propose a variational wave function for the condensate of Cooper triples in analogy with the Bardeen-Cooper-Schrieffer ground state, and we obtain the ground-state energy.
We theoretically discuss the possible condensation of Cooper triples, which correspond to a threebody 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.
We theoretically investigate ground-state properties of a three-component Fermi gas with pairwise contact interactions between different components near a triatomic resonance where bound trimers are about to appear. Using variational equations for in-medium two- and three-body cluster states in three dimensions, we elucidate the competition of pair and triple formations due to the Fermi surface effects. We present the ground-state phase diagram that exhibits transition from a Cooper pair to Cooper triple state and crossover from a Cooper triple to tightly bound trimer state at negative scattering lengths. This three-body crossover is analogous to the Bardeen-Cooper-Schrieffer to Bose-Einstein condensation crossover observed in a two-component Fermi gas. We predict that the threshold scattering length ${a}_{\ensuremath{-}}$ for three-body states can be shifted towards the weak-coupling side due to the emergence of Cooper triples.
We study the finite temperature-density phase diagram of an attractive fermionic system that supports two-body (dimer) and three-body (trimer) bound states in free space. Using interactions characteristic for nuclear systems, we obtain the critical temperature Tc2{T}_{c2}Tc2​ for the superfluid phase transition and the limiting temperature Tc3{T}_{c3}Tc3​ for the extinction of trimers. The phase diagram features a Cooper-pair condensate in the high-density, low-temperature domain which, with decreasing density, crosses over to a Bose condensate of strongly bound dimers. The high-temperature, low-density domain is populated by trimers whose binding energy decreases toward the density-temperature domain occupied by the superfluid and vanishes at a critical temperature Tc3>Tc2{T}_{c3}>{T}_{c2}Tc3​>Tc2​.