Quantum Lifshitz points and fluctuation-induced first-order phase transitions in imbalanced Fermi mixtures

Abstract

We perform a detailed analysis of the phase transition between the uniform superfluid and normal phases in spin- A nd mass-imbalanced Fermi mixtures. At mean-field level we demonstrate that at temperature T→0 the gradient term in the effective action can be tuned to zero for experimentally relevant sets of parameters, thus providing an avenue to realize a quantum Lifshitz point. We subsequently analyze damping processes affecting the order-parameter field across the phase transition. We show that in the low-energy limit, Landau damping occurs only in the symmetry-broken phase and affects exclusively the longitudinal component of the order-parameter field. It is however unavoidably present in the immediate vicinity of the phase transition at temperature T=0. We subsequently perform a renormalization group analysis of the system in a situation, where, at mean-field level, the quantum phase transition is second order (and not multicritical). We find that, at T sufficiently low, including the Landau-damping term in a form derived from the microscopic action destabilizes the renormalization group flow toward the Wilson-Fisher fixed point. This signals a possible tendency to drive the transition weakly first order by the coupling between the order-parameter fluctuations and fermionic excitations effectively captured by the Landau-damping contribution to the order-parameter action.