Observation of pinning mode of stripe phases of 2D systems in high   Landau levels
  We study the radio-frequency diagonal conductivities of the anisotropic stripe phases of higher Landau levels near half integer fillings. In the hard direction, in which larger dc resistivity occurs, the spectrum exhibits a striking resonance, while in the orthogonal, easy direction, no resonance is discernable. The resonance is interpreted as a pinning mode of the stripe phase. 
G. Sambandamurthy, R. M. Lewis, Han Zhu, Y. P. Chen, L. W. Engel, D.   C. Tsui, L. N. Pfeiffer and K. W. West