PINNING MODE RESONANCES OF TWO-DIMENSIONAL ELECTRON STRIPE PHASES AT HIGH LANDAU LEVELS

This paper presents the radio-frequency (rf) diagonal conductivity spectra of two-dimensional electrons in the second excited and higher Landau levels, and in particular shows isotropic pinning mode resonances in the bubble phases evolving into a highly anisotropic rf resonance in the stripe phase. The stripe phase resonance is observed for the rf electric field, Erf, along the "hard" direction, in which the dc higher resistivity occurs, but not for Erf along the orthogonal, "easy" direction. The resonance is naturally interpreted as a pinning mode of the stripe phase.