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Title: Resonantly paired fermionic superfluids

Abstract

We present a theory of a degenerate atomic Fermi gas, interacting through a narrow Feshbach resonance, whose position and therefore strength can be tuned experimentally, as demonstrated recently in ultracold trapped atomic gases. The distinguishing feature of the theory is that its accuracy is controlled by a dimensionless parameter proportional to the ratio of the width of the resonance to Fermi energy. The theory is therefore quantitatively accurate for a narrow Feshbach resonance. In the case of a narrow s-wave resonance, our analysis leads to a quantitative description of the crossover between a weakly paired BCS superconductor of overlapping Cooper pairs and a strongly paired molecular Bose-Einstein condensate of diatomic molecules. In the case of pairing via a p-wave resonance, that we show is always narrow for a sufficiently low density, we predict a detuning-temperature phase diagram, that in the course of a BCS-BEC crossover can exhibit a host of thermodynamically distinct phases separated by quantum and classical phase transitions. For an intermediate strength of the dipolar anisotropy, the system exhibits a p {sub x} + ip {sub y} paired superfluidity that undergoes a topological phase transition between a weakly coupled gapless ground state at large positive detuning and amore » strongly paired fully gapped molecular superfluid for a negative detuning. In two dimensions the former state is characterized by a Pfaffian ground state exhibiting topological order and non-Abelian vortex excitations familiar from fractional quantum Hall systems.« less

Authors:
 [1];  [2]
  1. Department of Physics, University of Colorado, Boulder, CO 80309 (United States). E-mail: victor.gurarie@colorado.edu
  2. Department of Physics, University of Colorado, Boulder, CO 80309 (United States)
Publication Date:
OSTI Identifier:
20845987
Resource Type:
Journal Article
Resource Relation:
Journal Name: Annals of Physics (New York); Journal Volume: 322; Journal Issue: 1; Other Information: DOI: 10.1016/j.aop.2006.10.009; PII: S0003-4916(06)00239-9; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ACCURACY; ANISOTROPY; BOSE-EINSTEIN CONDENSATION; COOPER PAIRS; EXCITATION; FERMI GAS; FERMIONS; GASES; GROUND STATES; P WAVES; PHASE DIAGRAMS; PHASE TRANSFORMATIONS; RESONANCE; S WAVES; SUPERCONDUCTORS; SUPERFLUIDITY; TOPOLOGY; VORTICES

Citation Formats

Gurarie, V., and Radzihovsky, L. Resonantly paired fermionic superfluids. United States: N. p., 2007. Web. doi:10.1016/j.aop.2006.10.009.
Gurarie, V., & Radzihovsky, L. Resonantly paired fermionic superfluids. United States. doi:10.1016/j.aop.2006.10.009.
Gurarie, V., and Radzihovsky, L. Mon . "Resonantly paired fermionic superfluids". United States. doi:10.1016/j.aop.2006.10.009.
@article{osti_20845987,
title = {Resonantly paired fermionic superfluids},
author = {Gurarie, V. and Radzihovsky, L.},
abstractNote = {We present a theory of a degenerate atomic Fermi gas, interacting through a narrow Feshbach resonance, whose position and therefore strength can be tuned experimentally, as demonstrated recently in ultracold trapped atomic gases. The distinguishing feature of the theory is that its accuracy is controlled by a dimensionless parameter proportional to the ratio of the width of the resonance to Fermi energy. The theory is therefore quantitatively accurate for a narrow Feshbach resonance. In the case of a narrow s-wave resonance, our analysis leads to a quantitative description of the crossover between a weakly paired BCS superconductor of overlapping Cooper pairs and a strongly paired molecular Bose-Einstein condensate of diatomic molecules. In the case of pairing via a p-wave resonance, that we show is always narrow for a sufficiently low density, we predict a detuning-temperature phase diagram, that in the course of a BCS-BEC crossover can exhibit a host of thermodynamically distinct phases separated by quantum and classical phase transitions. For an intermediate strength of the dipolar anisotropy, the system exhibits a p {sub x} + ip {sub y} paired superfluidity that undergoes a topological phase transition between a weakly coupled gapless ground state at large positive detuning and a strongly paired fully gapped molecular superfluid for a negative detuning. In two dimensions the former state is characterized by a Pfaffian ground state exhibiting topological order and non-Abelian vortex excitations familiar from fractional quantum Hall systems.},
doi = {10.1016/j.aop.2006.10.009},
journal = {Annals of Physics (New York)},
number = 1,
volume = 322,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • We map out the detuning-magnetization phase diagram for a magnetized (unequal number of atoms in two pairing hyperfine states) gas of fermionic atoms interacting via an s-wave Feshbach resonance (FR). The phase diagram is dominated by the coexistence of a magnetized normal gas and a singlet-paired superfluid with the latter exhibiting a BCS-Bose Einstein condensate crossover with reduced FR detuning. On the BCS side of strongly overlapping Cooper pairs, a sliver of finite-momentum paired Fulde-Ferrell-Larkin-Ovchinnikov magnetized phase intervenes between the phase-separated and normal states. In contrast, for large negative detuning a uniform, polarized superfluid, that is, a coherent mixture ofmore » singlet Bose-Einstein-condensed molecules and fully magnetized single-species Fermi sea, is a stable ground state.« less
  • We study resonantly-paired s-wave superfluidity in a degenerate gas of two species (hyperfine states labeled by {up_arrow}, {down_arrow}) of fermionic atoms when the numbers N {sub {up_arrow}} and N {sub {down_arrow}} of the two species are unequal, i.e., the system is 'polarized.' We find that the continuous crossover from the Bose-Einstein condensate (BEC) limit of tightly-bound diatomic molecules to the Bardeen-Cooper-Schrieffer (BCS) limit of weakly correlated Cooper pairs, studied extensively at equal populations, is interrupted by a variety of distinct phenomena under an imposed population difference {delta}N {identical_to} N {sub {up_arrow}} - N {sub {down_arrow}}. Our findings are summarized bymore » a 'polarization' ({delta}N) versus Feshbach-resonance detuning ({delta}) zero-temperature phase diagram, which exhibits regions of phase separation, a periodic FFLO superfluid, a polarized normal Fermi gas and a polarized molecular superfluid consisting of a molecular condensate and a fully polarized Fermi gas. We describe numerous experimental signatures of such phases and the transitions between them, in particular focusing on their spatial structure in the inhomogeneous environment of an atomic trap.« less
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  • It is proposed that in s-wave superfluids of cold fermionic atoms with laser-field-generated effective spin-orbit interactions, a topological phase with gapless edge states and Majorana fermion quasiparticles obeying non-Abelian statistics is realized in the case with a large Zeeman magnetic field. Our scenario provides a promising approach to the realization of quantum computation based on the manipulation of non-Abelian anyons via an s-wave Feshbach resonance.