Magnetic Feshbach resonances in Ba$^+$+Li collisions due to strong spin-orbit coupling

TL;DR

This study investigates how strong spin-orbit coupling affects magnetic Feshbach resonance spectra in ultracold Ba$^+$+Li collisions, revealing state-dependent resonance distributions and developing a model to explain these effects.

Contribution

It introduces a comprehensive computational model that explains the influence of spin-orbit coupling on resonance distributions in ultracold ion-atom collisions.

Findings

Resonance spectra depend strongly on Li hyperfine-Zeeman state.

Spin-orbit coupling increases the number of detectable resonances.

The model matches experimental data for the lowest Li state but not for the second-lowest state.

Abstract

We report a pronounced dependence of magnetic Feshbach resonance spectra on the initial hyperfine-Zeeman state of Li in ultracold $^{138}$Ba$^+$+$^6$Li collisions. The measured number and distribution of resonances differ significantly between the two lowest states despite their similar electron spin character. We address this puzzle by developing a comprehensive yet generic computational model calibrated against key statistical features in the experimental spectrum. We confirm that strong spin-orbit coupling induces essential changes in the distribution of resonances, leading to an increase in the number of resolvable resonances. Our model reproduces the statistics of the spectrum with the lowest Li state but struggles with the second-lowest state, where a significantly smaller number of resonances is experimentally observed.