S-wave-scattering resonances induced by dipolar interactions of polar molecules

We show that the s-wave-scattering resonances induced by dipolar interactions in polar molecular gases have a universal large and positive effective range, which is very different from Feshbach resonances previously realized in cold atoms before, where the effective range is either negligible or negative. Such a difference has important consequences in many-body physics. At a high-temperature regime, a positive effective range gives rise to a stronger repulsive interaction energy for positive scattering length, and a weaker attractive interaction energy for negative scattering length. At low temperatures, we study a polaron problem formed by a single-impurity molecule, and we find that the polaron binding energy increases at the BEC side and decreases at the BCS side. All these effects are opposite to narrow Feshbach resonances, where the effective range is negative.