Long-range influence of manipulating disordered insulators locally

Localization of wave functions is arguably the most familiar effect of disorder in quantum systems. It has been recently argued [V. Khemani, R. Nandkishore, and S. L. Sondhi, Nat. Phys. 11, 560 (2015)1745-247310.1038/nphys3344] that, contrary to naive expectation, manipulation of a localized site in the disordered medium may produce a disturbance over a length scale much larger than the localization length, ζ. Here we report on the observation of this nonlocal phenomenon in electronic transport experiments. Being a wave property, visibility of this effect hinges upon quantum coherence, and its spatial scale may be ultimately limited by the phase-coherent length of the disordered insulator. Evidence for quantum coherence in the Anderson-insulating phase may be obtained from magnetoresistance measurements which, however, are useful mainly in thin films. The technique used in this work offers an empirical method to measure this fundamental aspect of Anderson insulators even in relatively thick samples.