Spin-charge separation in a 1D Fermi gas with tunable interactions*

Ultracold atoms confined in optical lattices are a powerful tool for quantum simulation of complex many-body systems. We confine spin-1/2 atomic fermions (⁶Li) to one dimension and realize the Yang-Gaudin model, the low-energy behavior of which is expected to be that of a Tomonaga-Luttinger liquid [1]. Such liquids exhibit bosonic collective low-energy excitations and spin-charge separation. Using Bragg spectroscopy and a Feshbach resonance, we directly excite either the spin or charge wave with a tunable repulsive interaction strength. We observe the onset of spin-charge separation as interactions are increased from zero. The spin and charge excitation velocities are equal for the non-interacting case, while the charge-mode velocity increases and the spin-mode velocity decreases with increasing interaction, a hallmark of spin-charge separation. The excitation spectra provide access to the dynamic structure factors of each mode, which are in quantitative agreement with the Tomonaga-Luttinger liquid theory, including nonlinear corrections due to band-curvature and back-scattering.

[1] Ruwan Senaratne, Danyel Cavazos-Cavazos, Sheng Wang, Feng He, Aashish Kafle, Ya-Ting Chang, Han Pu, Xi-Wen Guan and Randall G. Hulet, arXiv:2111.11545 [cond-mat.quant-gas]