LAUSR

We have studied the collective spin-conserving collective excitation spectra in rotating diluted ultra-cold Bose atoms. Double roton-minima have been observed in the fractional quantum Hall (FQH) states for the two filling fractions (ν) of the first series of Jain's composite fermion sequences. The obtained roton-minima for ν = 1/4 are at the wave-vectors 1.26 and 2.38 and the roton-minima for ν = 1/6 have been shifted to 1.08 and 2.06. Such shift of roton-minima is attributed due to strong correlation between the particles in bosonic FQH-system. Moreover, the number of roton minima observed depends upon number of attached fluxes as well as the ranges of interaction between the particles.