Topic: Observation of quantum liquids: Spin-Charge Separation, FFLO and Luther-Emery states
Speaker: Prof. Xi-Wen Guan
Coordinates: PCFT C1124, 16:00, Thursday, November 27
Abstract:
The low-energy excitations of a one-dimensional (1D) two-component repulsive ultracold atomic Fermi gas, i.e. Yang-Gaudin model, decompose into two collective motions (carrying either only spin or charge degree of freedom), a hallmark of the unique 1D spin-charge separation phenomenon. However, the 1D interacting fermions with attractive interactions exhibit novel Bardeen-Cooper-Schrieffer pairing states strongly dependent on polarization, forming the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-pairing state or a Luther-Emery liquid. The latter presents the fully paired state with an energy gap in spin excitations and gapless charge excitations.
This talk discusses these starkly different features of 1D interacting fermions via the Bethe ansatz and bosonization. Using a Feshbach resonance to access both repulsive and attractive interaction regions with 6Li atoms, we measured spin and charge dynamical structure factors via Bragg spectroscopy—and definitively observed spin-charge separation, consistent with nonlinear Luttinger liquids. Unlike repulsive interactions, we found spin waves propagate faster than charge density waves for the attractive interaction, revealing the pair-breaking nature of spin excitationsn and an inversion of the classic spin-charge separation. Additionally, the RF spectra are consistent with an atom/molecule mixture stabilized by finite temperature and a spin-imbalance.
References:
He, Jiang, Lin, Hulet, Pu, Guan, Phys. Rev. Lett. 125, 190401 (2020).
Senaratne, et. al., Pu, Guan, Hulet, Science 376, 1305 (2022).
Kafle, et. al. Pu, Guan, Hulet, in preparation, 2025
Hai-Ying Cui, et al., and Xiwen Guan, in preparation, 2025