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  • Letter

Polarizing the medium: Fermion-mediated interactions between bosons

Dong-Chen Zheng, Chun-Rong Ye, Lin Wen, and Renyuan Liao
Phys. Rev. A 103, L021301 – Published 5 February 2021
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    Abstract

    We consider a homogeneous mixture of bosons and polarized fermions. We find that long-range and attractive fermion-mediated interactions between bosons have dramatic effects on the properties of the bosons. We construct the phase diagram spanned by boson-fermion mass ratio and boson-fermion scattering parameter. It consists of a stable region of mixing and unstable region toward phase separation. In the stable mixing phase, the collective long-wavelength excitations can either be well behaved with infinite lifetime or be finite in lifetime suffered from the Landau damping. We examine the effects of the induced interaction on the properties of weakly interacting bosons. It turns out that the induced interaction not only enhances the repulsion between the bosons against collapse but also enhances the stability of the superfluid state by suppressing quantum depletion.

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    • Received 1 July 2020
    • Revised 15 January 2021
    • Accepted 19 January 2021

    DOI:https://doi.org/10.1103/PhysRevA.103.L021301

    ©2021 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Bose-Einstein condensatesCold atoms & matter wavesFermi gasesMixtures of atomic and/or molecular quantum gases
    Atomic, Molecular & Optical

    Authors & Affiliations

    Dong-Chen Zheng1,2, Chun-Rong Ye1,2, Lin Wen3,*, and Renyuan Liao1,2,†

    • 1Fujian Provincial Key Laboratory for Quantum Manipulation and New Energy Materials, College of Physics and Energy, Fujian Normal University, Fuzhou 350117, China
    • 2Fujian Provincial Collaborative Innovation Center for Advanced High-Field Superconducting Materials and Engineering, Fuzhou 350117, China
    • 3College of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 401331, China

    • *wlqx@cqnu.edu.cn
    • †ryliao@fjnu.edu.cn

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    Issue

    Vol. 103, Iss. 2 — February 2021

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    Images

    • Figure 1
      Figure 1

      (a) The shade region is the range where the imaginary part of the polarization function differs from zero, and it is referred as particle-hole continuum, since it is the region of single-particle excitations, whereby a particle below the Fermi surface is excited to above the Fermi surface. Outside this region, it is not possible to conserve energy and wave vector in a single-particle excitation process. (b) The imaginary part of the polarization function ImΠ(q,ω) [in units of d(EF)] as a function of frequencies ω at given different typical momentum amplitude q.

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    • Figure 2
      Figure 2

      Properties of the Bogoliugov quasiparticles: (a) the excitation energy ω/EF where kFaFB=0.3 and (b) the Landau damping rate γ/EF where mB/mF=1. The shade region is referred as particle-hole continuum. The quasiparticle spectrum laying outside of the shadow region is well-defined, being immune from the Landau damping. We set kFaBB=0.3 and nB/nF=0.2.

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    • Figure 3
      Figure 3

      Phase diagram spanned by mass ratio mB/mF and interspecies coupling strength kFaFB. PS stands for phase separation and QP stands for quasi-particle with infinite lifetime. Here we set kFaBB=0.4, which sets bosons in a weakly interacting regime.

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    • Figure 4
      Figure 4

      Correction to the ground-state energy per density ΔEG/nBEF (a) as a function of mass ratio mB/mF where kFaFB=0.3 and (b) as a function of boson-fermion scattering length kFaFB where mB/mF=1. We set kFaBB=0.3.

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    • Figure 5
      Figure 5

      Quantum depletion of the condensates nex/nB (a) as a function of mass ratio mB/mF where kFaFB=0.3 and (b) as a function of boson-fermion scattering parameter kFaFB where mB/mF=1. The vertical dash line intercepts with maxima of the curves at mB=mF. We set kFaBB=0.3.

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