Influence of the Intraspecies Scattering Length on the Three-Body Parameter in Efimov-Unfavored Systems

Although the Efimov effect is primarily known for three identical bosons, it also occurs in three-body heteronuclear systems (BBX) with at least two resonant pairs (i.e., the interspecies scattering length a_BX = ∞) [1,2]. Efimov resonances associated with heteronuclear trimers have been observed in ultracold two-species gases near an interspecies Feshbach resonance [3,4]. However, in most studies, the intraspecies scattering length a_BB has been treated as a background parameter with no significant influence on the locations of the Efimov resonances a_-⁽ⁿ⁾ (in a_BX) or, in turn, on the three-body parameter (3BP). In Efimov-unfavored systems (m_B < m_X), a_BB is expected to play a crucial role due to the large discrepancy between the Efimov scaling parameters for two (s₀) and three (s₀^*) resonant pairs [2], highlighting the importance of the intraspecies interaction. This work investigates the dependence of the Efimov resonances a_-⁽ⁿ⁾, particularly the 3BP a_-⁽⁰⁾, on a_BB in Efimov-unfavored systems. It is found that both the magnitude and sign of the intraspecies scattering length a_BB can drastically impact the 3BP in these systems.



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