Magnetoroton modes at sub-Zeeman energies in a filling factor range around 1/3

Sutirtha Mukherjee, Sudhansu S. Mandal

Published 2014-11-24Version 1

The nature of the excitations causing the modes at sub-Zeeman energies in a filling factor range around 1/3 first observed more than a decade ago by Dujovne et al. [Phys. Rev. Lett. 90, 036803 (2003)] still remains unresolved. We make a strong case that these modes are due to the "magnetorotons" in spinless neutral excitations. By calculating the dispersion of Girvin-MacDonald-Platzman mode using the recently proposed "unconventional" ground states for the fractional quantum Hall effect observed at the filling factors $\nu = 4/11$, 4/13, 5/13, 5/17, 3/8, and 6/17, we show a generic formation of the primary magnetorotons for all these $\nu$ at very low momenta with energies lower than a typical Zeeman energy in the semiconductor systems. We further propose an experimental criterion to test our theory.