Fictitious fields for light: topological insulators and pseudomagnetism

Condensed Matter Seminars

Speaker: Mikael Rechtsman, Technion
Date & Time: September 19, 2013 14:00 - 15:00
Location: UBC, Hennings 318
Local Contact: Marcel Franz
Intended Audience: Graduate

In this talk I present two examples (time permitting) in which ‘fictitious fields’ can lead to surprising photon dynamics that would be difficult (if not impossible) to achieve with real fields. The first is the case of ‘photonic’ topological insulators.  Topological insulators are solid-state materials that are insulators in the bulk but have intrinsic surface states that behave metallically, and are completely robust to any type of defects or disorder.  In other words, when a surface electron wave in a TI encounters a defect, it simply goes around it without scattering, exhibiting – quite strikingly – perfect transmission.  Here I present the observation of a photonic topological insulator: a topological insulator where the wavefunction describes photons, rather than electrons.  The structure is an array of helical waveguides (the helicity generates a fictitious circularly-polarized electric field that leads to the TI behavior), and light propagating through it is ‘topologically forbidden’ from scattering.

The second example is artificial magnetic fields (‘pseudomagnetism’) in photonic lattice structures.  In nearly any material, magnetic response is negligible in the optical regime.  Here I show experimental results demonstrating how straining the structure inhomogeneously is equivalent to an extremely strong magnetic field. The effect of the field is to collapse the spatial photonic spectrum into ‘photonic Landau levels’ – spectral regions of extremely high density-of-states.  High photonic density-of-states enables strong light-matter interaction over large areas for a broad range of potential applications.