TKM Institutsseminar |
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Speaker: | Darryl Foo |
Date: | 06/04/2021 14:00 |
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Where: | Zoom |
Affiliation: | University of Cambridge, UK and Centre for advanced 2D materials, Singapore |
Host: | Igor Gornyi |
Abstract
Weak attractive interactions in a spin-balanced fermion gas are known to induce a Cooper pairing instability where the fermion pairs have zero net momentum, leading to BCS superconductivity. Extensions for spin-imbalanced systems include breached superfluids, Fulde-Ferrell-Larkin-Ovchinnikov theory, and pair density wave theory. We propose a further extension of a superconducting state, dubbed a communal pairing state, whose underlying components are superpositions of Cooper pairs that share minority-spin fermions. This state includes correlations between all available fermions on both Fermi surfaces and is shown to be energetically favourable to the Fulde-Ferrell-Larkin-Ovchinnikov state. Our numerical quantum Monte Carlo study of finite spin-imbalanced systems provides clear evidence of the existence of such exotic pairing states. In spin-balanced systems, temporal fluctuations of the order parameter promote communal pairing, leading to a widening in momentum space of the superconducting gap and a decrease of the energy and chemical potential.