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Cuestas E, Majtey AP. A generalized molecule approach capturing the Feshbach-induced pairing physics in the BEC-BCS crossover. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:255601. [PMID: 33848988 DOI: 10.1088/1361-648x/abf7a2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Accepted: 04/13/2021] [Indexed: 06/12/2023]
Abstract
By including the effect of a trap with characteristic energy given by the Fermi temperatureTFin a two-body two-channel model for Feshbach resonances, we reproduce the measured binding energy of ultracold molecules in a40K atomic Fermi gas. We also reproduce the experimental closed-channel fractionZacross the BEC-BCS crossover and into the BCS regime of a6Li atomic Fermi gas. We obtain the expected behaviorZ∝TFat unitarity, together with the recently measured proportionality constant. Our results are also in agreement with recent measurements of theZdependency onTFon the BCS side, where a significant quantitative discrepancy between experimental data and theory's predictions has been repeatedly reported. In order to contrast with future experiments we report the proportionality constant at unitarity betweenZandTFpredicted by our model for a40K atomic Fermi gas.
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Affiliation(s)
- Eloisa Cuestas
- Facultad de Matemática, Astronomía, Física y Computación (FaMAF), Universidad Nacional de Córdoba (UNC), Av. Medina Allende s/n, Ciudad Universitaria, X5000HUA, Córdoba, Argentina
- Instituto de Física Enrique Gaviola (IFEG), Consejo de Investigaciones Científicas y Técnicas de la República Argentina (CONICET), Córdoba, Argentina
| | - Ana P Majtey
- Facultad de Matemática, Astronomía, Física y Computación (FaMAF), Universidad Nacional de Córdoba (UNC), Av. Medina Allende s/n, Ciudad Universitaria, X5000HUA, Córdoba, Argentina
- Instituto de Física Enrique Gaviola (IFEG), Consejo de Investigaciones Científicas y Técnicas de la República Argentina (CONICET), Córdoba, Argentina
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2
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Richie-Halford A, Drut JE, Bulgac A. Emergence of a Pseudogap in the BCS-BEC Crossover. PHYSICAL REVIEW LETTERS 2020; 125:060403. [PMID: 32845679 DOI: 10.1103/physrevlett.125.060403] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Accepted: 07/13/2020] [Indexed: 06/11/2023]
Abstract
Strongly correlated Fermi systems with pairing interactions become superfluid below a critical temperature T_{c}. The extent to which such pairing correlations alter the behavior of the liquid at temperatures T>T_{c} is a subtle issue that remains an area of debate, in particular regarding the appearance of the so-called pseudogap in the BCS-BEC crossover of unpolarized spin-1/2 nonrelativistic matter. To shed light on this, we extract several quantities of crucial importance at and around the unitary limit, namely, the odd-even staggering of the total energy, the spin susceptibility, the pairing correlation function, the condensate fraction, and the critical temperature T_{c}, using a nonperturbative, constrained-ensemble quantum Monte Carlo algorithm.
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Affiliation(s)
- Adam Richie-Halford
- Department of Physics, University of Washington, Seattle, Washington 98195-1560, USA
| | - Joaquín E Drut
- Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599, USA
| | - Aurel Bulgac
- Department of Physics, University of Washington, Seattle, Washington 98195-1560, USA
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3
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Kwon WJ, Del Pace G, Panza R, Inguscio M, Zwerger W, Zaccanti M, Scazza F, Roati G. Strongly correlated superfluid order parameters from dc Josephson supercurrents. Science 2020; 369:84-88. [DOI: 10.1126/science.aaz2463] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2019] [Accepted: 04/27/2020] [Indexed: 11/02/2022]
Affiliation(s)
- W. J. Kwon
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
| | - G. Del Pace
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
- Department of Physics and Astronomy, University of Florence, 50019 Sesto Fiorentino, Italy
| | - R. Panza
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
| | - M. Inguscio
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
- Department of Engineering, Campus Bio-Medico University of Rome, 00128 Rome, Italy
| | - W. Zwerger
- Physics Department, Technische Universität München, 85747 Garching, Germany
| | - M. Zaccanti
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
| | - F. Scazza
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
| | - G. Roati
- Istituto Nazionale di Ottica del Consiglio Nazionale delle Ricerche (CNR-INO), 50019 Sesto Fiorentino, Italy
- European Laboratory for Nonlinear Spectroscopy (LENS), 50019 Sesto Fiorentino, Italy
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4
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López Ríos P, Perali A, Needs RJ, Neilson D. Evidence from Quantum Monte Carlo Simulations of Large-Gap Superfluidity and BCS-BEC Crossover in Double Electron-Hole Layers. PHYSICAL REVIEW LETTERS 2018; 120:177701. [PMID: 29756819 DOI: 10.1103/physrevlett.120.177701] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2017] [Indexed: 06/08/2023]
Abstract
We report quantum Monte Carlo evidence of the existence of large gap superfluidity in electron-hole double layers over wide density ranges. The superfluid parameters evolve from normal state to BEC with decreasing density, with the BCS state restricted to a tiny range of densities due to the strong screening of Coulomb interactions, which causes the gap to rapidly become large near the onset of superfluidity. The superfluid properties exhibit similarities to ultracold fermions and iron-based superconductors, suggesting an underlying universal behavior of BCS-BEC crossovers in pairing systems.
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Affiliation(s)
- Pablo López Ríos
- Max-Planck Institute for Solid State Research, Heisenbergstraße 1, 70569 Stuttgart, Germany
- Theory of Condensed Matter Group, Cavendish Laboratory, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Andrea Perali
- School of Pharmacy, Physics Unit, University of Camerino, 62032 Camerino (MC), Italy
| | - Richard J Needs
- Theory of Condensed Matter Group, Cavendish Laboratory, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - David Neilson
- School of Science and Technology, Physics Division, University of Camerino, 62032 Camerino (MC), Italy
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
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5
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Sharma RO, Saini LK, Bahuguna BP. Diffusion Monte Carlo study of excitons and biexcitons in a mass-asymmetric electron-hole bilayer. Phys Chem Chem Phys 2017; 19:20778-20785. [PMID: 28740991 DOI: 10.1039/c7cp02934a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We employed the diffusion Monte Carlo method, under fixed node approximation, to investigate the various ground state properties of a mass-asymmetric electron-hole bilayer system. Particularly, we calculated the ground state energy, the condensation fraction c, and the pair correlation function g(r) at density rs = 5 a.u. for the inter-planer distance d ≤ 0.5 a.u. Based on the characteristics of condensate faction and pair correlation functions, we found the phase transition from the excitonic fluid phase to the biexcitonic fluid phase at d = 0.24 a.u. We also analytically calculated the critical layer separation dcrit for biexciton stability, the value for which was almost double the d = 0.24 a.u.
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Affiliation(s)
- Rajesh O Sharma
- Applied Physics Department, Sardar Vallabhbhai National Institute of Technology Surat, 395007, India.
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6
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Valtolina G, Burchianti A, Amico A, Neri E, Xhani K, Seman JA, Trombettoni A, Smerzi A, Zaccanti M, Inguscio M, Roati G. Josephson effect in fermionic superfluids across the BEC-BCS crossover. Science 2015; 350:1505-8. [DOI: 10.1126/science.aac9725] [Citation(s) in RCA: 106] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Accepted: 11/13/2015] [Indexed: 11/02/2022]
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7
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Maezono R, Ríos PL, Ogawa T, Needs RJ. Excitons and biexcitons in symmetric electron-hole bilayers. PHYSICAL REVIEW LETTERS 2013; 110:216407. [PMID: 23745904 DOI: 10.1103/physrevlett.110.216407] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Indexed: 06/02/2023]
Abstract
Symmetric electron-hole bilayer systems have been studied at zero temperature using the diffusion quantum Monte Carlo method. A flexible trial wave function is used that can describe fluid, excitonic, and biexcitonic phases. We calculate condensate fractions and pair correlation functions for a large number of densities r(s) and layer separations d. At small d we find a one-component fluid phase, an excitonic fluid phase, and a biexcitonic fluid phase, and the transitions among them appear to be continuous. At d=0, excitons appear to survive down to about r(s)=0.5 a.u., and biexcitons form at r(s)>2.5 a.u.
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Affiliation(s)
- Ryo Maezono
- School of Information Science, JAIST, Asahidai 1-1, Nomi, Ishikawa, 923-1292, Japan
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8
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Zhou K, Zhang Z. Opposite effect of spin-orbit coupling on condensation and superfluidity. PHYSICAL REVIEW LETTERS 2012; 108:025301. [PMID: 22324694 DOI: 10.1103/physrevlett.108.025301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2011] [Indexed: 05/31/2023]
Abstract
We investigate the effects of Rashba-type spin-orbit coupling (SOC) on the condensed density and superfluid density tensor of a two-component Fermi gas in the BCS-BEC crossover at zero temperature. In anisotropic three dimensions (3D), we find that SOC has an opposite effect on condensation (enhanced) and superfluidity (suppressed in the SOC direction), and this effect becomes most pronounced for very weak interactions and the SOC strength being larger than a characteristic value. Furthermore, as functions of SOC strength, the condensed density changes monotonically for all interaction parameters, while the superfluid density has a minimum when the interaction parameter is below a critical value. We also discuss the isotropic two-dimensional case where analytical expressions for the gap and number equations are obtained and the same phenomena are found as that of the 3D case.
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Affiliation(s)
- Kezhao Zhou
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, People's Republic of China
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9
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Drut JE, Lähde TA, Ten T. Momentum distribution and contact of the unitary Fermi gas. PHYSICAL REVIEW LETTERS 2011; 106:205302. [PMID: 21668239 DOI: 10.1103/physrevlett.106.205302] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2011] [Revised: 04/11/2011] [Indexed: 05/30/2023]
Abstract
We calculate the momentum distribution n(k) of the unitary Fermi gas by using quantum Monte Carlo calculations at finite temperature T/ϵ(F) as well as in the ground state. At large momenta k/k(F), we find that n(k) falls off as C/k⁴, in agreement with the Tan relations. From the asymptotics of n(k), we determine the contact C as a function of T/ϵ(F) and present a comparison with theory. At low T/ϵ(F), we find that C increases with temperature, and we tentatively identify a maximum around T/ϵ(F) ≃ 0.4. Our calculations are performed on lattices of spatial extent up to N(x) = 14 with a particle number per unit volume of ≃ 0.03-0.07.
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Affiliation(s)
- Joaquín E Drut
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545-0001, USA
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10
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Bertaina G, Giorgini S. BCS-BEC crossover in a two-dimensional Fermi gas. PHYSICAL REVIEW LETTERS 2011; 106:110403. [PMID: 21469845 DOI: 10.1103/physrevlett.106.110403] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2010] [Revised: 02/04/2011] [Indexed: 05/30/2023]
Abstract
We investigate the crossover from Bardeen-Cooper-Schrieffer (BCS) superfluidity to Bose-Einstein condensation (BEC) in a two-dimensional Fermi gas at T=0 using the fixed-node diffusion Monte Carlo method. We calculate the equation of state and the gap parameter as a function of the interaction strength, observing large deviations compared to mean-field predictions. In the BEC regime our results show the important role of dimer-dimer and atom-dimer interaction effects that are completely neglected in the mean-field picture. Results on Tan's contact parameter associated with short-range physics are also reported along the BCS-BEC crossover.
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Affiliation(s)
- G Bertaina
- Institute of Theoretical Physics, Ecole Polytechnique Fédérale de Lausanne EPFL, CH-1015 Lausanne, Switzerland
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11
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Bajdich M, Kolorenč J, Mitas L, Reynolds P. Pairing in Cold Atoms and other Applications for Quantum Monte Carlo methods. ACTA ACUST UNITED AC 2010. [DOI: 10.1016/j.phpro.2010.01.199] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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12
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Orso G. BCS-BEC crossover in a random external potential. PHYSICAL REVIEW LETTERS 2007; 99:250402. [PMID: 18233500 DOI: 10.1103/physrevlett.99.250402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2007] [Revised: 10/24/2007] [Indexed: 05/25/2023]
Abstract
We investigate the ground state properties of a disordered superfluid Fermi gas across the BCS-BEC (Bose-Einstein condensate) crossover. We show that, for weak disorder, both the depletion of the condensate fraction of pairs and the normal fluid density exhibit a nonmonotonic behavior as a function of the interaction parameter 1/k{F}a, reaching their minimum value near unitarity. We find that, moving away from the weak-coupling BCS regime, Anderson's theorem ceases to apply and the superfluid order parameter is more and more affected by the random potential.
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Affiliation(s)
- G Orso
- Laboratoire Physique Théorique et Modèles Statistiques, Université Paris Sud, Bat. 100, 91405 Orsay Cedex, France
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13
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Blume D, von Stecher J, Greene CH. Universal properties of a trapped two-component fermi gas at unitarity. PHYSICAL REVIEW LETTERS 2007; 99:233201. [PMID: 18233361 DOI: 10.1103/physrevlett.99.233201] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2007] [Indexed: 05/25/2023]
Abstract
We treat the trapped two-component Fermi system, in which unlike fermions interact through a two-body short-range potential having no bound state but an infinite scattering length. By accurately solving the Schrödinger equation for up to N=6 fermions, we show that no many-body bound states exist other than those bound by the trapping potential, and we demonstrate unique universal properties of the system: Certain excitation frequencies are separated by 2variant Planck's over 2piomega, the wave functions agree with analytical predictions and a virial theorem is fulfilled. Further calculations up to N=30 determine the excitation gap, an experimentally accessible universal quantity, and it agrees with recent predictions based on a density functional approach.
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Affiliation(s)
- D Blume
- Department of Physics and JILA, University of Colorado, Boulder, Colorado 80309-0440, USA
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14
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Sensarma R, Randeria M, Trivedi N. Can one determine the underlying fermi surface in the superconducting state of strongly correlated systems? PHYSICAL REVIEW LETTERS 2007; 98:027004. [PMID: 17358639 DOI: 10.1103/physrevlett.98.027004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2006] [Indexed: 05/14/2023]
Abstract
The question of determining the underlying Fermi surface (FS) that is gapped by superconductivity (SC) is of central importance in strongly correlated systems, particularly in view of angle-resolved photoemission experiments. Here we explore various definitions of the FS in the superconducting state using the zero-energy Green's function, the excitation spectrum, and the momentum distribution. We examine (a) d-wave SC in high-Tc cuprates, and (b) the s-wave superfluid in the BCS-Bose-Einstein condensation (BEC) crossover. In each case we show that the various definitions agree, to a large extent, but all of them violate the Luttinger count and do not enclose the total electron density. We discuss the important role of chemical potential renormalization and incoherent spectral weight in this violation.
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Affiliation(s)
- Rajdeep Sensarma
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
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Stewart JT, Gaebler JP, Regal CA, Jin DS. Potential energy of a 40K Fermi gas in the BCS-BEC crossover. PHYSICAL REVIEW LETTERS 2006; 97:220406. [PMID: 17155785 DOI: 10.1103/physrevlett.97.220406] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2006] [Indexed: 05/12/2023]
Abstract
We present a measurement of the potential energy of an ultracold trapped gas of 40K atoms in the BCS-BEC crossover and investigate the temperature dependence of this energy at a wide Feshbach resonance, where the gas is in the unitarity limit. In particular, we study the ratio of the potential energy in the region of the unitarity limit to that of a noninteracting gas, and in the T=0 limit we extract the universal many-body parameter beta. We find beta=-0.54_{-0.12};{+0.05}; this value is consistent with previous measurements using 6Li atoms and also with recent theory and Monte Carlo calculations. This result demonstrates the universality of ultracold Fermi gases in the strongly interacting regime.
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Affiliation(s)
- J T Stewart
- JILA, Quantum Physics Division, National Institute of Standards and Technology and Department of Physics, University of Colorado, Boulder, Colorado 80309-0440, USA.
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Lobo C, Recati A, Giorgini S, Stringari S. Normal state of a polarized fermi gas at unitarity. PHYSICAL REVIEW LETTERS 2006; 97:200403. [PMID: 17155666 DOI: 10.1103/physrevlett.97.200403] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2006] [Indexed: 05/12/2023]
Abstract
We study the Fermi gas at unitarity and at T=0 by assuming that, at high polarizations, it is a normal Fermi liquid composed of weakly interacting quasiparticles associated with the minority spin atoms. With a quantum Monte Carlo approach we calculate their effective mass and binding energy, as well as the full equation of state of the normal phase as a function of the concentration x=n downward arrow/n upward arrow of minority atoms. We predict a first order phase transition from normal to superfluid at x(c)=0.44 corresponding, in the presence of harmonic trapping, to a critical polarization P(c)=(N upward arrow - N downward arrow/(N upward arrow + N downward arrow)=77%. We calculate the radii and the density profiles in the trap and predict that the frequency of the spin dipole mode will be increased by a factor of 1.23 due to interactions.
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Affiliation(s)
- C Lobo
- Dipartimento di Fisica, Università di Trento and CNR-INFM BEC Center, I-38050 Povo, Trento, Italy
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Burovski E, Prokof'ev N, Svistunov B, Troyer M. Critical temperature and thermodynamics of attractive fermions at unitarity. PHYSICAL REVIEW LETTERS 2006; 96:160402. [PMID: 16712207 DOI: 10.1103/physrevlett.96.160402] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2006] [Indexed: 05/09/2023]
Abstract
The unitarity regime of the BCS-BEC crossover can be realized by diluting a system of two-component lattice fermions with an on-site attractive interaction. We perform a systematic-error-free finite-temperature simulation of this system by diagrammatic determinant Monte Carlo method. The critical temperature in units of Fermi energy is found to be T(C)/epsilonF=0.152(7). We also report the behavior of the thermodynamic functions, and discuss the issues of thermometry of ultracold Fermi gases.
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Affiliation(s)
- Evgeni Burovski
- Department of Physics, University of Massachusetts, Amherst, Massachusetts 01003, USA
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18
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Bulgac A, Drut JE, Magierski P. Spin 1/2 fermions in the unitary regime: a superfluid of a new type. PHYSICAL REVIEW LETTERS 2006; 96:090404. [PMID: 16606247 DOI: 10.1103/physrevlett.96.090404] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2005] [Revised: 11/14/2005] [Indexed: 05/08/2023]
Abstract
We study, in a fully nonperturbative calculation, a dilute system of spin 1/2 interacting fermions, characterized by an infinite scattering length at finite temperatures. Various thermodynamic properties and the condensate fraction are calculated and we also determine the critical temperature for the superfluid-normal phase transition in this regime. The thermodynamic behavior appears as a rather surprising and unexpected mélange of fermionic and bosonic features. The thermal response of a spin 1/2 fermion at the BCS-BEC crossover should be classified as that of a new type of superfluid.
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Affiliation(s)
- Aurel Bulgac
- Department of Physics, University of Washington, Seattle, Washington 98195-1560, USA
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19
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Regal CA, Greiner M, Giorgini S, Holland M, Jin DS. Momentum distribution of a Fermi gas of atoms in the BCS-BEC crossover. PHYSICAL REVIEW LETTERS 2005; 95:250404. [PMID: 16384438 DOI: 10.1103/physrevlett.95.250404] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2005] [Indexed: 05/05/2023]
Abstract
We observe dramatic changes in the atomic momentum distribution of a Fermi gas in the crossover region between the BCS theory superconductivity and Bose-Einstein condensation (BEC) of molecules. We study the shape of the momentum distribution and the kinetic energy as a function of interaction strength. The momentum distributions are compared to a mean-field crossover theory, and the kinetic energy is compared to theories for the two weakly interacting limits. This measurement provides a unique probe of pairing in a strongly interacting Fermi gas.
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Affiliation(s)
- C A Regal
- JILA, Quantum Physics Division, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309-0440, USA.
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