title: Microwave resonance of the bubble phases in 1/4 and 3/4 filled high Landau levels.
abstract: We have measured the diagonal conductivity, sigma(xx), in the microwave regime of an ultrahigh mobility two dimensional electron system. We find a sharp resonance in Re[sigma(xx)] versus frequency when nu>4 and the partial filling of the highest Landau level, nu(*), is approximately 1/4 or 3/4 and temperatures <0.1 K. The resonance appears for a range of nu(*) from 0.20 to 0.38 and again from 0.64 to 0.80. The peak frequency f(pk) changes from approximately 500 to approximately 150 MHz as nu(*)=1/2 is approached. This range of f(pk) shows no dependence on nu where the resonance is observed. The quality factor, Q, of the resonance is maximum at about nu(*)=0.25 and 0.74. We interpret the resonance as due to a pinning mode of the bubble phase crystal.
authors.affiliation: National High Magnetic Field Lab and Department of Physics, Florida State University, Tallahassee, Florida 32306, USA.
authors.forename: R M
authors.initials: RM
authors.lastname: Lewis
authors.forename: P D
authors.initials: PD
authors.lastname: Ye
authors.forename: L W
authors.initials: LW
authors.lastname: Engel
authors.forename: D C
authors.initials: DC
authors.lastname: Tsui
authors.forename: L N
authors.initials: LN
authors.lastname: Pfeiffer
authors.forename: K W
authors.initials: KW
authors.lastname: West