Two-dimensional mixture of dipolar fermions: Equation of state and magnetic phases

Abstract

We study a two-component mixture of fermionic dipoles in two dimensions at zero temperature, interacting via a purely repulsive 1/r 3 potential. This model can be realized with ultracold atoms or molecules, when their dipole moments are aligned in the confinement direction orthogonal to the plane. We characterize the unpolarized mixture by means of the Diffusion Monte Carlo technique. Computing the equation of state, we identify the regime of validity for a mean-field theory based on a low-density expansion and compare our results with the hard-disk model of repulsive fermions. At high density, we address the possibility of itinerant ferromagnetism, namely whether the ground state can be fully polarized in the fluid phase. Within the fixed-node approximation, we show that the accuracy of Jastrow-Slater trial wave functions, even with the typical two-body backflow correction, is not sufficient to resolve the relevant energy differences. By making use of the iterativebackflow improved trial wave functions, we observe no signature of a fully-polarized ground state up to the freezing density. arXiv:1812.08064v2 [cond-mat.quant-gas]

Two-dimensional repulsive Fermi polarons with short- and long-range interactions

“…The antisymmetric wave function for the bath, Ψ A (R ↑ ), is a Slater determinant, where we use plane waves as single-particle orbitals. These orbitals, which correspond to the nodal surface of the free Fermi gas, are accurate enough for the low densities considered here, as it was shown in a recent work [27].…”

“…For a dipolar system, the Hamiltonian (1) can be written in dimensionless form by expressing all distances in units of the characteristic length r 0 = mC dd /(4π 2 ) and energies in units of ǫ 0 = 2 /mr 2 0 . Hence, properties of the homogeneous system are governed by the dimensionless density nr 2 0 encoding the strength of the interactions, as it was done in previous works [27,49,50]. Although in three dimensions the dipole-dipole potential is long ranged, in two dimensions it is not.…”

“…The dependence of the mean-field prediction (9) on a free parameter c 0 is a peculiarity of 2D systems that is related to the features of scattering theory in 2D [56]. This free parameter is related to a characteristic energy scale of the system [27,47]. In the present work, we set it to the value c 0 = e 2γ π/2 ≃ 4.98, corresponding to using an energy scale equal to the Fermi energy E F = 2 2 πn/m.…”

“…In the latter case, we assume that all the dipolar moments are polarized along the direction perpendicular to the plane of motion, so that the interaction between them is isotropic (see for instance Ref. [27]).…”

Few-body bound states of two-dimensional bosons

“…The most recent experiments of dipolar gases are done with Dysprosium [24,25] and Erbium [26]. Many interesting phenomena have been observed and predicted in dipolar gases, for example, dipolar Bose supersolid stripes [27], dipolar quantum mixtures [28,29], formation of a crystal phase [30,31], and a pair superfluid [32][33][34].…”