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Soviet Journal of Low Temperature Physics

Possibility of superconducting type correlations in repulsive Fermi systems

Tatiana N. Antsygina, V. A. Slyusarev

Published May 1, 1989• 0 citations
Publisher

Abstract

The possibility of the existence of superconducting correlations is analyzed by using the Hubbard model with repulsion on the basis of the generalized self-consistent field method (without resorting to the auxiliary field formalism or equivalent approximations based on the “spherical” type uncontrollable approximations). It is shown that a superconducting solution does not exist in this method under the condition forbidding a double occupancy of a lattice site. The results are compared with the recent data.

DOI
10.1063/10.0032174

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The possibility of the existence of superconducting correlations is analyzed by using the Hubbard model with repulsion on the basis of the generalized self-consistent field method (without resorting to the auxiliary field formalism or equivalent approximations based on the “spherical” type uncontrollable approximations). It is shown that a superconducting solution does not exist in this method under the condition forbidding a double occupancy of a lattice site. The results are compared with the recent data.
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We study the possibility of a pairing instability in Fermi systems with a purely repulsive interaction potential. The effective interaction between particles at the Fermi surface is shown to contain a contribution from the fermionic background. This contribution is attractive and in many cases it overshadows the interactive potential in the pairing channels with nonzero orbital angular momenta. In particular, we show that 3D Fermi gas with repulsive interaction is unstable against p-pairing. Both the value of T c and its field dispersion are consistent with the experimental data for pure 3 He . It is also shown that in a magnetic field and in the two-band model there is the possibility of a significant mcrease of T c . We also consider the situation in two dimensions, where the effect of the fermionic background is much weaker than in the 3D case. Nevertheless, we show that the positive-U Hubbard model may have an intrinsic instability at arbitrarily small carrier densities. In particular, the Hubbard model with hopping between nearest neighbors is unstable against d-wave pairing with dxy symmetry of the gap wave function. The superconducting states we study correspond to the actual minima of the Free energy.
Ground-state properties of the repulsive Hubbard model on a cubic lattice are investigated by means of the auxiliary-field quantum Monte Carlo method. We focus on low-density systems with varying on-site interaction U/tU/tU/t, as a model relevant to recent experiments on itinerant ferromagnetism in a dilute Fermi gas with contact interaction. Twist-average boundary conditions are used to eliminate open-shell effects and large lattice sizes are studied to reduce finite-size effects. The sign problem is controlled by a generalized constrained path approximation. We find no ferromagnetic phase transition in this model. The ground-state correlations are consistent with those of a paramagnetic Fermi liquid.