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Quasicrystals are aperiodic structures with rotational symmetries forbidden to conventional periodic crystals, examples of which can be found in aluminium alloys, polymers, and even ancient Islamic art. Here, we present direct experimental observation of disorder-enhanced wave transport in quasicrystals, which contrasts directly with the characteristic suppression of transport by disorder. Our experiments are carried out in photonic quasicrystals, where we find that increasing disorder leads to enhanced expansion of the beam propagating through the medium. By further increasing the disorder, we observe that the beam progresses through a regime of diffusive-like transport until it finally transitions to Anderson localization and the suppression of transport. We study this fundamental phenomenon, and elucidate its origins by relating it to the basic properties of quasicrystalline media in the presence of disorder. Anderson localization (1), a fundamental concept in solidstate physics, describes how introducing disorder can transform a conducting crystal into an insulator. This prediction and subsequent experiments have shown that generally disorder works to arrest transport, in periodic systems (crystals) containing disorder (2¨C4) as well as in fully random potentials (5¨C9). However, some systems still pose fundamental challenges to this concept, most notably, quasicrystals. Quasicrystals (QCs) (10, 11) constitute an intermediate phase between fully periodic and fully disordered media: they do not have a unit cell and do not exhibit translation symmetry, but nevertheless possess noncrystallographic rotational symmetry, long-range order and display Bragg diffraction. Although many of the properties of QCs are now well understood, some fundamental questions remain. Perhaps one of the most intriguing questions related to QCs has to do with transport. Opposite to crystals containing disorder, which exhibit Anderson localization, it has been suggested that disorder can enhance transport in QCs (12, 13). Indirect experiments indicated that indeed, in some regime, increasing disorder could enhance transport |
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