Effective field theory of boson-fermion mixtures and bound fermion states on a vortex of boson superfluid

TL;DR

This paper develops a Galilean invariant effective field theory for boson-fermion mixtures, analyzing bound fermion states on superfluid vortices, and applies it to helium mixtures and cold Fermi gases to predict bound state phenomena.

Contribution

It introduces a simple criterion for bound state existence in boson-fermion mixtures and applies it to real systems, providing new insights into vortex-bound fermion states.

Findings

Predicts infinite bound states for certain angular momenta in He3-He4 mixtures.

Identifies conditions for higher angular momentum bound states in polarized Fermi gases.

Provides parameter estimates from experimental data for helium mixtures.

Abstract

We construct a Galilean invariant low-energy effective field theory of boson-fermion mixtures and study bound fermion states on a vortex of boson superfluid. We derive a simple criterion to determine for which values of the fermion angular momentum l there exist an infinite number of bound energy levels. We apply our formalism to two boson-fermion mixed systems: the dilute solution of He3 in He4 superfluid and the cold polarized Fermi gas on the BEC side of the "splitting point". For the He3-He4 mixture, we determine parameters of the effective theory from experimental data as functions of pressure. We predict that infinitely many bound He3 states on a superfluid vortex with l=-2,-1,0 are realized in a whole range of pressure, 0\sim20 atm, where experimental data are available. As for the cold polarized Fermi gas, while only S-wave (l=0) and P-wave (l=\pm1) bound fermion states are possible in the BEC limit, those with higher negative angular momentum become available as one moves away from the BEC limit.