Pairing and repulsive effective interactions

T. Espinosa-Ortega, Oleksandr Kyriienko, Ivan Andreevich Shelykh

We consider a mixture of two neutral cold Fermi gases with repulsive interactions. We show that in some region of the parameter space of the system the effective attraction between fermions of the same type can appear due to the exchange of collective excitations. This leads to the formation of BCS pairing in the case where bare interatomic interactions are repulsive.

Steven R. White, Douglas J. Scalapino, Robert L. Sugar +2 more

Particle-hole-magnetic and particle-particle-pairing susceptibilities can be expressed in terms of dressed Green's functions and interaction vertices. Using quantum Monte Carlo simulation techniques, the effect of the interaction vertices is examined to determine the sign and relative magnitude of the effective pairing interaction in various channels for the two-dimensional Hubbard model. Near half filling we find that the singlet ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ pairing interaction is the most attractive. The extended near-neighbor $s$ interaction is also weakly attractive, while the singlet ${s}_{\mathrm{xy}}$ and ${d}_{\mathrm{xy}}$ and the triplet ${p}_{x}$ interactions are repulsive.

Barry R. Holstein

Barry R. Holstein

Joachim Kerner, Maximilian Pechmann

In this paper we investigate the effect of repulsive pair interactions on Bose–Einstein condensation in a well-established random one-dimensional system known as the Luttinger–Sy model at positive temperature. We study separately hard core interactions as well as a class of more general repulsive interactions, also allowing for a scaling of certain interaction parameters in the thermodynamic limit. As a main result, we prove in both cases that for sufficiently strong interactions all eigenstates of the non-interacting one-particle Luttinger–Sy Hamiltonian are P \mathbb {P} -almost surely not macroscopically occupied. We also outline an extension of the results to sufficiently localized one-particle states.