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

Abstract

We study the repulsive polaron problem in a two-component two-dimensional system of fermionic atoms. We use two different interaction models: a short-range (hard-disk) potential and a dipolar potential. In our approach, all the atoms have the same mass and we consider the system to be composed of a uniform bath of a single species and a single atomic impurity. We use the diffusion Monte Carlo method to evaluate polaron properties such as its chemical potential and pair distribution functions, together with a discussion on the deficit of volume induced by the impurity. We also evaluate observables that allow us to determine the validity of the quasi-particle picture: the quasi-particle residue and the effective mass of the polaron. Employing two different potentials allows us to identify the universality regime, where the properties depend only on the gas parameter na 2 s fixed by the bath density and the two-dimensional scattering length.

Few-body bound states of two-dimensional bosons

“…The QMC methods have been demonstrated to give an accurate description of correlated quantum systems at zero and low temperature [37]. Examples include ultracold gases with bosonic [38,39] and fermionic statistics [17,29], quantum solids [43,44], and Helium [45,46].…”

“…For an atomic condensate the ground-state energy dependence on small polarization is quadratic 17) where E(0) is the ground-state energy of the balanced system and χ s is the spin susceptibility associated with the dispersion of spin waves of the magnetization density n t − n d with speed of sound c s = n/mχ s . In this case the low-lying excitations are coupled phonon modes of the two layers [32].…”

“…The simplest form of the localization term is a Gaussian function Eq. (7.11) 17) where α is the localization strength, r j is the position vector of the particle j and R j is the chain center of mass to which particle r j belongs. The chain center of mass R j is given by Eq.…”

“…Since the experimental observation of the BEC, there have been intense theoretical and experimental efforts to understand ultracold bosonic and fermionic gases. Interesting quantum phases have been predicted and experimentally realized in these systems, for example, quantum droplets in a mixture of Bose-Einstein condensates [5][6][7][8] and in dipolar bosonic gases [9][10][11][12], quantum droplets in optical lattices [13,14], impurities of atoms immersed in a gas of fermions [15][16][17] or bosons [18][19][20], the so-called polaron problem, among others. At very low densities, some ultracold gases can be characterized by the s-wave scattering length, which means that they can be described by an isotropic, short-range, contact interaction model.…”

“…Both VMC and DMC methods have been shown to give an accurate description of correlated quantum systems [37]. Examples include ultradilute bosonic [38,39] and fermionic mixtures [29], Bose [20,40] and Fermi [17] polarons, dipolar Bose supersolid stripes [27], Bose gas subject to a multi-rod lattice [41], and ultracold quantum gases with spin-orbit interactions [42].…”