76th Annual Gaseous Electronics Conference
Volume 68, Number 9
Monday–Friday, October 9–13, 2023;
Michigan League, Ann Arbor, Michigan
Session IW5: Poster Session II; Exhibition & Coffee (4:00pm-6:00pm)
4:00 PM,
Wednesday, October 11, 2023
Room: Michigan League, Ballroom
Abstract: IW5.00005 : Resonant processes and their impact in transport properties*
Abstract
Presenter:
Robin Cote
(University of Massachusetts Boston)
Author:
Robin Cote
(University of Massachusetts Boston)
Resonant exchange is a general process playing a key role in many-body dynamics and transport phenomena, such as spin, charge, or excitation diffusion. The underlying process is described by the resonant exchange cross section σexc. A prime example is the diffusion of an ion A+ in its parent neutral gas A. In fact, the charge actually behaves as a hole (h) at ultralow tem peratures, hopping from atom to atom instead of staying on its heavy center (the ion) [1]. We have predicted a faster diffusion coefficient for the hole (Dh) than if the charge was diffusing via collision (Dcoll). In this work, we show that the exchange symmetry for identical (homonuclear) atom-ion system leads to special outcomes for ion transport in ultracold experiments. We compute the two body charge hopping probabilities and rates, which are used to model charge hopping in the dynamics of an ultracold 6/7Li+ ion immersed within an ultracold gas of 6/7Li atoms at micro-Kelvin temperatures [2]. We show that the charge hopping and collisional diffusion compete, giving unique results leading to charge trapping in regions of high atomic density gradient, leading to a region of "negative" diffusion. As mentioned above, the dynamics is dictated by σexc. In previous work [3], we showed that the locking of s-wave phase shifts could be used to explain the behavior of exc at ultracold tem peratures. Moreover, we found an unexpected consequence of phase-shift locking; namely, the behavior of the resonant-exchange cross section over a broad range of energies is largely dictated by s-wave scattering, whose inuence extends high above the s-wave Wigner regime. We now generalize our treatment to higher energies and derive an analytical expression for the resonant-exchange cross section which accounts not only for the locking of phase shifts, but also for their gradual unlocking as the energy increases. We find good agreement between the computed (fully quantal) cross section and our newly obtained result, which we illustrate for resonant charge-transfer in ion-atom collisions.
[1] R. Côté, PRL 85, 5316 (2000).
[2] N. Joshi, M. Niranjan, A. Pandey, O. Dulieu, R. Côté., S.A. Rangwala, PRA 105, 063311 (2022).
[3] R. Côté and I. Simbotin, PRL 121, 173401 (2018).
*This was supported by the National Science Foundation (NSF), Grant No. PHY-2034284.