Stable pair liquid phase in fermionic systems

Abstract

We predict the existence of a pair-liquid phase in lattice fermion systems with finite-range attractive interactions. This exotic state competes on one side with a normal Fermi liquid of unpaired fermions and on the other side with a phase-separated state where all fermions are coupled into macroscopic clusters. We show that such a phase is absent in bosonic systems and therefore is protected by the exclusion principle. In contrast with zero-range attractive systems where clustering of more than two fermions is directly prohibited, here quantum statistics acts dynamically and in a more subtle way. Since a many-fermion wave function must have nodes, the cluster formation threshold is larger than the pair formation threshold. By directly solving a four-body Schroedinger equation on one- and two-dimensional lattices, we map the boundaries of pair stability. The pair liquid phase should be observable in cold atom systems. We also discuss implications for the preformed-pair mechanism of high-temperature superconductivity.

Published version. 23 pages, 13 figures, 34 pages of supplemental material

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Cited by in corpus (3)

• Two-particle bound states on a lattice
• Ubiquitous light real-space pairing from long-range hopping and interactions
• Real-space d-wave superconductivity from weak attraction