Spin relaxation in ultracold spin-orbit coupled $^{40}$K gas

TL;DR

This paper investigates anomalous spin relaxation behaviors in ultracold $^{40}$K gases with strong spin-orbit coupling, revealing complex regimes influenced by scattering, polarization, and effective magnetic fields, differing from conventional weak magnetic field scenarios.

Contribution

It uncovers novel spin relaxation regimes in ultracold gases under strong spin-orbit coupling, highlighting the effects of Hartree-Fock fields and scattering length variations on relaxation dynamics.

Findings

Identification of four distinct spin relaxation regimes at small polarization.

Suppression of transverse spin relaxation by Hartree-Fock effective magnetic field.

Dependence of relaxation regimes on scattering length and polarization.

Abstract

We report the anomalous Dyakonov-Perel' spin relaxation in ultracold spin-orbit coupled $^{40}$K gas when the coupling between $|9/2,9/2\ >$ and $|9/2,7/2\ >$ states (atcing as the effective Zeeman magnetic field) is much stronger than the spin-orbit coupled field. Both the transverse and longitudinal spin relaxations are investigated with small and large spin polarizations. It is found that with small spin polarization, the transverse (longitudinal) spin relaxation is divided into four (two) regimes: the normal weak scattering regime, the anomalous Dyakonov-Perel'-like regime, the anomalous Elliott-Yafet-like regime and the normal strong scattering regime (the anomalous Elliott-Yafet-like regime and the normal strong scattering regime), with only the normal weak scattering regime being in the weak scattering limit. This is very different from the conventional situation under the weak magnetic field, which is divided into the weak and strong scattering regimes according to the weak/strong scattering limit. With large spin polarization, we find that the Hartree-Fock self-energy, which acts as an effective magnetic field, can markedly suppress the transverse spin relaxation in both weak and strong scattering limits. Moreover, by noting that as both the momentum relaxation time and the Hartree-Fock effective magnetic field vary with the scattering length in cold atoms, the anomalous Dyakonov-Perel'-like regime is suppressed and the transverse spin relaxation is hence divided into three regimes in the scattering length dependence: the normal weak scattering regime, the anomalous Elliott-Yafet-like regime and the strong scattering regime. On the other hand, the longitudinal spin relaxation is again divided into the anomalous EY-like and normal strong scattering regimes. ...