We consider a bilayer geometry where a single impurity moves in a two-dimensional plane and is coupled, via dipolar interactions, to a two-dimensional system of fermions residing in the second layer. Dipoles in both layers point in the same direction oriented by an external field perpendicular to the plane of motion. We use quantum Monte Carlo methods to calculate the binding energy and the effective mass of the impurity at zero temperature as a function of the distance between layers as well as of the in-plane interaction strength. In the regime where the fermionic dipoles form a Wigner crystal, the physics of the impurity can be described in terms of a polaron coupled to the bath of lattice phonons. By reducing the distance between layers this polaron exhibits a crossover from a free-moving to a tightly bound regime where its effective mass is orders of magnitude larger than the bare mass.
We consider a bilayer geometry where a single impurity moves in a two-dimensional plane and is coupled, via dipolar interactions, to a two-dimensional system of fermions residing in the second layer. Dipoles in both layers point in the same direction oriented by an external field perpendicular to the plane of motion. We use quantum Monte Carlo methods to calculate the binding energy and the effective mass of the impurity at zero temperature as a function of the distance between layers as well as of the in-plane interaction strength. In the regime where the fermionic dipoles form a Wigner crystal, the physics of the impurity can be described in terms of a polaron coupled to the bath of lattice phonons. By reducing the distance between layers this polaron exhibits a crossover from a free-moving to a tightly bound regime where its effective mass is orders of magnitude larger than the bare mass.
We consider a bilayer geometry where a single impurity moves in a two-dimensional plane and is coupled, via dipolar interactions, to a two-dimensional system of fermions residing in the second layer. Dipoles in both layers point in the same direction oriented by an external field perpendicular to the plane of motion. We use quantum Monte Carlo methods to calculate the binding energy and the effective mass of the impurity at zero temperature as a function of the distance between layers as well as of the in-plane interaction strength. In the regime where the fermionic dipoles form a Wigner crystal, the physics of the impurity can be described in terms of a polaron coupled to the bath of lattice phonons. By reducing the distance between layers this polaron exhibits a crossover from a free-moving to a tightly bound regime where its effective mass is orders of magnitude larger than the bare mass.
We study the Fermi polaron problem with dipolar fermions in a bilayer geometry, where a single dipolar particle in one layer interacts with a Fermi sea of dipolar fermions in the other layer. By evaluating the polaron spectrum, we obtain the appearance of a series of attractive branches when the distance between the layers diminishes. We relate these to the appearance of a series of bound two-dipole states when the interlayer dipolar interaction strength increases. By inspecting the orbital angular-momentum component of the polaron branches, we observe an interchange of orbital character when system parameters such as the gas density or the interlayer distance are varied. Furthermore, we study the possibility that the lowest energy two-body bound state spontaneously acquires a finite center-of-mass momentum when the density of fermions exceeds a critical value, and we determine the dominating orbital angular momenta that characterize the pairing. Finally, we propose to use the tunneling rate from and into an auxiliary layer as an experimental probe of the impurity spectral function.
The liquid and crystal phases of a single-component Fermi gas with dipolar interactions are investigated using quantum Monte Carlo methods in two spatial dimensions and at zero temperature. The dipoles are oriented by an external field perpendicular to the plane of motion, resulting in a purely repulsive 1/r(3) interaction. In the liquid phase we calculate the equation of state as a function of the interaction strength and other relevant properties characterizing the Fermi-liquid behavior: effective mass, discontinuity at the Fermi surface, and pair correlation function. In the high density regime we calculate the equation of state of the Wigner crystal phase and the critical density of the liquid to solid quantum phase transition. Close to the freezing density we also search for the existence of a stripe phase, but such a phase is never found to be energetically favorable.
We investigate the BCS-BEC crossover in a bilayer system of fermionic dipoles at zero temperature using the fixed-node diffusion Monte Carlo technique. The dipoles are confined on two parallel planes separated by a distance $\ensuremath{\lambda}$ and are aligned perpendicular to the planes by an external field. The interlayer pairing, which is responsible for the superfluid behavior of the system, crosses from a weak- to a strong-coupling regime by reducing the separation distance $\ensuremath{\lambda}$. For a fixed in-plane density equal in the two layers, we calculate the ground-state energy, the chemical potential, the pairing gap, and the quasiparticle dispersion as a function of the interlayer separation. At large $\ensuremath{\lambda}$ one recovers the ground-state energy of a single layer of fermions, and at small $\ensuremath{\lambda}$ one recovers that of a single layer of composite bosons with twice the particle mass and the dipole moment. The superfluid gap varies from the exponentially small BCS result to half of the large two-body binding energy in the Bose-Einstein condensate (BEC) regime of strong interlayer pairing. Results are compared with the predictions of the simplest mean-field theory valid in the low-density limit, and deviations are observed both in the BCS regime, where in-plane repulsions are important, and in the BEC regime, where the mean-field approach fails to describe the physics of composite dipolar bosons.
We investigate the behavior of identical dipolar fermions with aligned dipole moments in two-dimensional multilayers at zero temperature. We consider density instabilities that are driven by the attractive part of the dipolar interaction and, for the case of bilayers, we elucidate the properties of the stripe phase recently predicted to exist in this interaction regime. When the number of layers is increased, we find that this ``attractive'' stripe phase exists for an increasingly larger range of dipole angles, and if the interlayer distance is sufficiently small, the stripe phase eventually spans the full range of angles, including the situation where the dipole moments are aligned perpendicular to the planes. However, in this regime, we expect the behavior to be strongly modified by the binding of dipoles between layers. In the limit of an infinite number of layers, we derive an analytic expression for the mean-field interlayer effects in the density-density response function and, using this result, we find that the stripe phase is replaced by a collapse of the dipolar system.
We study the quasiparticle properties of a dipolar impurity immersed in a two-dimensional dipolar bath. We use the ab initio diffusion Monte Carlo technique to determine the polaron energy, effective mass, and quasiparticle residue. We find that both the polaron energy and quasiparticle residue follow a universal behavior with respect to the polarization angle when properly scaled in terms of the scattering length. This trend is maintained over a wide range of values of the gas parameter, even in the highly correlated regime. Instead, the effective mass shows growing anisotropy as the tilting angle is increased, which is induced, mainly, by the anisotropy of the impurity-boson dipole-dipole interaction. Surprisingly, the effective mass is larger in the direction of minimum interparticle repulsion. Finally, we use our Monte Carlo results to check the accuracy of perturbative approaches and determine their range of validity in terms of the gas parameter.