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Title: Comparative study of BCS-BEC crossover theories above T{sub c}: The nature of the pseudogap in ultracold atomic Fermi gases

Abstract

This article presents a comparison of two finite-temperature BCS-Bose-Einstein condensation (BEC) crossover theories above the transition temperature: Nozieres-Schmitt-Rink (NSR) theory and finite-T extended BCS-Leggett theory. The comparison is cast in the form of numerical studies of the behavior of the fermionic spectral function both theoretically and as constrained by (primarily) radio frequency (rf) experiments. Both theories include pair fluctuations and exhibit pseudogap effects, although the nature of this pseudogap is very different. The pseudogap in finite-T extended BCS-Leggett theory is found to follow a BCS-like dispersion which, in turn, is associated with a broadened BCS-like self-energy, rather more similar to what is observed in high-temperature superconductors (albeit, for a d-wave case). The fermionic quasiparticle dispersion is different in NSR theory and the damping is considerably larger. We argue that the two theories are appropriate in different temperature regimes with the BCS-Leggett approach being more suitable nearer to condensation. There should, in effect, be little difference at higher T as the pseudogap becomes weaker and where the simplifying approximations used in the BCS-Leggett approach break down. On the basis of momentum-integrated rf studies of unpolarized gases, it would be difficult to distinguish which theory is the better one. A full comparisonmore » for polarized gases is not possible since it is claimed that there are inconsistencies in the NSR approach (not found in the BCS-Leggett scheme). Future experiments along the lines of momentum-resolved experiments look to be very promising in distinguishing the two theories.« less

Authors:
; ; ;  [1]
  1. James Franck Institute and Department of Physics, University of Chicago, Chicago, Illinois 60637 (United States)
Publication Date:
OSTI Identifier:
21408294
Resource Type:
Journal Article
Journal Name:
Physical Review. A
Additional Journal Information:
Journal Volume: 81; Journal Issue: 2; Other Information: DOI: 10.1103/PhysRevA.81.023622; (c) 2010 The American Physical Society; Journal ID: ISSN 1050-2947
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; APPROXIMATIONS; BOSE-EINSTEIN CONDENSATION; COMPARATIVE EVALUATIONS; D WAVES; DISPERSIONS; FERMI GAS; FERMIONS; FLUCTUATIONS; HIGH-TC SUPERCONDUCTORS; NUMERICAL ANALYSIS; RADIOWAVE RADIATION; SELF-ENERGY; SPECTRAL FUNCTIONS; TRANSITION TEMPERATURE; CALCULATION METHODS; ELECTROMAGNETIC RADIATION; ENERGY; EVALUATION; FUNCTIONS; MATHEMATICS; PARTIAL WAVES; PHYSICAL PROPERTIES; RADIATIONS; SUPERCONDUCTORS; THERMODYNAMIC PROPERTIES; TYPE-II SUPERCONDUCTORS; VARIATIONS

Citation Formats

Chien, C -C, Hao, Guo, Yan, He, and Levin, K. Comparative study of BCS-BEC crossover theories above T{sub c}: The nature of the pseudogap in ultracold atomic Fermi gases. United States: N. p., 2010. Web. doi:10.1103/PHYSREVA.81.023622.
Chien, C -C, Hao, Guo, Yan, He, & Levin, K. Comparative study of BCS-BEC crossover theories above T{sub c}: The nature of the pseudogap in ultracold atomic Fermi gases. United States. https://doi.org/10.1103/PHYSREVA.81.023622
Chien, C -C, Hao, Guo, Yan, He, and Levin, K. Mon . "Comparative study of BCS-BEC crossover theories above T{sub c}: The nature of the pseudogap in ultracold atomic Fermi gases". United States. https://doi.org/10.1103/PHYSREVA.81.023622.
@article{osti_21408294,
title = {Comparative study of BCS-BEC crossover theories above T{sub c}: The nature of the pseudogap in ultracold atomic Fermi gases},
author = {Chien, C -C and Hao, Guo and Yan, He and Levin, K},
abstractNote = {This article presents a comparison of two finite-temperature BCS-Bose-Einstein condensation (BEC) crossover theories above the transition temperature: Nozieres-Schmitt-Rink (NSR) theory and finite-T extended BCS-Leggett theory. The comparison is cast in the form of numerical studies of the behavior of the fermionic spectral function both theoretically and as constrained by (primarily) radio frequency (rf) experiments. Both theories include pair fluctuations and exhibit pseudogap effects, although the nature of this pseudogap is very different. The pseudogap in finite-T extended BCS-Leggett theory is found to follow a BCS-like dispersion which, in turn, is associated with a broadened BCS-like self-energy, rather more similar to what is observed in high-temperature superconductors (albeit, for a d-wave case). The fermionic quasiparticle dispersion is different in NSR theory and the damping is considerably larger. We argue that the two theories are appropriate in different temperature regimes with the BCS-Leggett approach being more suitable nearer to condensation. There should, in effect, be little difference at higher T as the pseudogap becomes weaker and where the simplifying approximations used in the BCS-Leggett approach break down. On the basis of momentum-integrated rf studies of unpolarized gases, it would be difficult to distinguish which theory is the better one. A full comparison for polarized gases is not possible since it is claimed that there are inconsistencies in the NSR approach (not found in the BCS-Leggett scheme). Future experiments along the lines of momentum-resolved experiments look to be very promising in distinguishing the two theories.},
doi = {10.1103/PHYSREVA.81.023622},
url = {https://www.osti.gov/biblio/21408294}, journal = {Physical Review. A},
issn = {1050-2947},
number = 2,
volume = 81,
place = {United States},
year = {2010},
month = {2}
}