Lab. de Phys. de la Matiere Condensee, CNRS URA 190, Faculte des Sciences, Parc Valrose, B.P. 70, 06108 Nice Cedex 02, France
The extreme sensitivity of wave propagation on the presence of disorder near remnant geometric Bragg resonance (band edges) is exhibited experimentally for the first time using surface acoustic waves on very weakly corrugated solids. Anderson localization is identified by measuring the spatial structure of proper modes with an optical diffraction experiment and is found to occur most strongly precisely at the two borders of a remnant stop band. Exponentially decaying localized modes are decorated by a speckle-like wave pattern, which constitutes an observable fingerprint of the random system. The amplitude of this spatial wave structure is found to exhibit a marked maximum at band edges thus providing a novel signature of localization, which used to probe localization in the interior of the remnant stop bands.