Dr. Mikael Rechtsman
Technion - Israel Institute of Technology

The theory of Anderson localization states that disorder in crystalline solids can act to inhibit electronic transport because it causes extended Bloch states to be replaced with localized states. Anderson localization is a general wave phenomenon not specific to electrons, and so when it was realized that it could be observed in disordered photonic structures, a flurry of research was carried out on experimentally observing the localization of light by disorder. In the first part of my talk, I will present our experimental demonstration of a counterintuitive effect: disorder-enhanced transport in quasicrystals (directly opposite to the inhibition of transport in periodic crystals). Quasicrystals are structures that are ordered but not periodic. Specifically, they contain long-range rotational order with symmetries that are forbidden to periodic systems (for example, 5-fold rotational symmetry). Photonic quasicrystals have shown promise as low-index-contrast band gap materials due to the near-isotropy of their quasi-Brillouin zone. Our observation explains and provides proof for what occurs in solid-state quasicrystals (which are found in certain metal alloys): when these materials are more disordered (i.e., with more structural defects), their conductivity increases.

In the second part of my talk, I will discuss our observation of band gaps in amorphous photonic lattices, wherein waveguides are arranged much like atoms in a liquid. The very presence of a band gap is not obvious at all: band gaps are commonly thought to open as a result of Bragg scattering (which means long-range order), and liquids have only short-range order. As with quasicrystals, amorphous photonic crystals are good candidates for low-index-contrast band gap materials. I will discuss some implications of band gaps in amorphous systems such as what happens to the effective mass, as well as amorphous gap solitons.

Mikael Rechtsman is an Azrieli Postdoctoral Fellow at the Technion – Israel Institute of Technology in Prof. Mordechai Segev’s group. Originally from Toronto, he received his B.S. degree from M.I.T. in 2003 and his Ph.D. from Princeton in 2008, both in physics. In his Ph.D., he worked with Salvatore Torquato, Frank Stillinger and Paul Steinhardt on topics in soft-matter physics, statistical mechanics, and photonics. Before moving to the Technion in early 2010, he was a Courant Instructor in the New York University mathematics department. He is the recipient of the NSERC graduate award and the Azrieli fellowship. His research centers on experimental and theoretical aspects of complex photonic systems, including amorphous photonic crystals, photonic quasicrystals, PT-breaking photonics, optical graphene, negative-radiation-pressure structures, as well as photonic applications to soft-matter physics. Dr. Rechtsman’s articles have been published in various scientific journals, including the Journal of Chemical Physics, Physical Review Letters, and Science.