Universal spin dynamics in two-dimensional Fermi gases

TL;DR

This paper investigates spin transport in a two-dimensional Fermi gas, demonstrating universal diffusion behavior and observing a very low spin diffusion constant, with insights into spin-wave modes near hydrodynamic conditions.

Contribution

It provides the first measurement of the lowest transverse spin diffusion constant in a 2D Fermi gas and explores spin dynamics across interaction regimes.

Findings

Measured transverse spin diffusion constant of 0.25(3) hbar/m

Observed coherent spin-wave mode with mode softening near hydrodynamics

Demonstrated universal spin diffusion behavior at unitarity

Abstract

Harnessing spins as carriers for information has emerged as an elegant extension to the transport of electrical charges. The coherence of such spin transport in spintronic circuits is determined by the lifetime of spin excitations and by spin diffusion. Fermionic quantum gases are a unique system to study the fundamentals of spin transport from first principles since interactions can be precisely tailored and the dynamics is on time scales which are directly observable. In particular at unitarity, spin transport is dictated by diffusion and is expected to reach a universal, quantum-limited diffusivity on the order of hbar/m. Here, we study the non-equilibrium dynamics of a two-dimensional Fermi gas following a quench into a metastable, transversely polarized spin state. Using the spin-echo technique, we measure the yet lowest transverse spin diffusion constant of 0.25(3) hbar/m. For weak interactions, we observe a coherent collective transverse spin-wave mode that exhibits mode softening when approaching the hydrodynamic regime.