Modelling Two-Roton Bound State Formation in Fractional Quantum Hall System

Composite Fermion approach using extensive and parallalized numerical analysis has recently established a two-roton bound state as the lowest energy long wavelength neutral excitation of FQHE for finite particle (N~30) system. By focussing on the "oriented dipole" character of magneto roton, we model the two roton problem and solve it variationally (analytically) to find a two-roton bound state with binding energy which is in good agreement with the composite fermion numerical results.Comment: 4 pages, REVTEX file, 3 figures, Minor changes, Accepted for publication in Physical Review Letter

Sound velocity and multibranch bogoliubov spectrum of an elongated fermi superfluid in the BEC-BCS crossover

We study properties of excited states of an elongated Fermi superfluid along the Bose-Einstein-condensate-BCS crossover including the unitarity limit. Analytic expressions for the sound velocity in an inhomogeneous as well as homogeneous Fermi superfluid along the crossover are obtained on the basis of the hydrodynamic theory. The complete excitation spectrum of axial quasiparticles with various discrete radial nodes is presented. We discuss the feasibility of measuring the sound velocity and the multibranch Bogoliubov spectrum experimentally