s-Wave Interaction in a Two-Species Fermi-Fermi Mixture at a Narrow Feshbach Resonance

Abstract

We investigate s-wave interactions in a two-species Fermi-Fermi mixture of 6Li and 40K. We develop for this case the method of cross-dimensional relaxation and find from a kinetic model, Monte Carlo simulations, and measurements that the individual relaxation rates differ due to the mass difference. The method is applied to measure the elastic cross section at the Feshbach resonance that we previously used for the production of heteronuclear molecules. Location (B0=155.09(5) G) and width are determined for this resonance. This reveals that molecules are being produced on the atomic side of the resonance within a range related to the Fermi energies, therefore establishing the first observation of a many body effect in the crossover regime of a narrow Feshbach resonance.

Excitation properties and effects of mass imbalance in the BCS-BEC crossover regime of an ultracold Fermi gas

“…(27) is reduced to the previous result in the T -matrix approximation [53], when one retains the term to O( 2 pg ) in Eq. (26).…”

“…Since the achievement of the superfluid phase transition in 40 K [1] and 6 Li [2][3][4] Fermi gases, various possibilities beyond this simplest s-wave pairing state have been discussed in this field, such as a p-wave superfluid [5][6][7][8][9][10][11][12][13], the Sarma phase [14][15][16][17], a dipolar Fermi condensate [18][19][20][21][22], and a mass-imbalanced Fermi superfluid [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]. Although none of these states has been observed yet, the high tunability of cold Fermi gases makes us expect that some of them may be realized in the near future.…”

“…Among various possibilities discussed in ultracold Fermi gases, in this paper, we pick up a hetero-pairing state in the presence of mass imbalance [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]. In this state, Cooper pairs are formed between different species with different masses, which is quite different from the ordinary homo-Cooper pairs in metallic superconductivity.…”

“…Thus, the mass-imbalanced superfluid Fermi gas is related to various aspects of Fermi superfluid physics. At present, gas mixtures * rhanai@rk.phys.keio.ac.jp of two different fermionic species [23][24][25][26][27][28][29], as well as 40 K-6 Li hetero-pairs [25,28], have been realized.…”

Investigation of Feshbach resonances in ultracold K40 spin mixtures

“…Feshbach resonances have been found in many bosonic as well as fermionic atomic systems (see [1][2][3][4][5] and references therein). The isotope 40 K constitutes one of the work horses in current experiments with ultracold fermions and provides a rich ground-state structure allowing for the realization of binary and multi-component spin mixtures [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] as well as several Bose-Fermi [24][25][26][27][28][29][30] and Fermi-Fermi mixtures [31][32][33][34][35]. In the energetically-lowest hyperfine manifold with total angular momentum f = 9/2 ten magnetic spin states are available ranging from m = −9/2, .…”