Dipolar Fermions in Layered Systems

Congjun Wu, J. E. Hirsch

Georg M. Bruun

Antonio Tiene, Andrés Tamargo Bracho, Meera M. Parish +2 more

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.

Chen-Yen Lai, Shan-Wen Tsai

Michele Callegari, Meera M. Parish, Francesca Maria Marchetti

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.

Brandon P. van Zyl, W. Ferguson

The liquid-to-ordered phase transition in a bilayer system of fermions is studied within the context of our recently proposed density-functional theory [B. P. van Zyl, W. Kirkby, and W. Ferguson, Phys. Rev. A 92, 023614 (2015)]. In each two-dimensional layer, the fermions interact via a repulsive, isotropic dipolar interaction. The presence of a second layer introduces an attractive interlayer interaction, thereby allowing the presence of inhomogeneous density phases which would otherwise be energetically unfavorable. For any fixed layer separation, we find an instability to a commensurate one-dimensional stripe phase in each layer, which always precedes the formation of a triangular Wigner crystal. However, at a certain fixed coupling, tuning the separation can lead to the system favoring a commensurate triangular Wigner crystal, or one-dimensional stripe phase, completely bypassing the Fermi liquid state. While other crystalline symmetries, with energies lower than the liquid phase can be found, they are never allowed to form owing to their high energetic cost relative to the triangular Wigner crystal and stripe phase.