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SUMMARY:Symmetry and topology in optical and plasmonic materials - Matthia
 s Saba (Université de Fribourg)
DTSTART:20230822T133000Z
DTEND:20230822T140000Z
UID:TALK202576@talks.cam.ac.uk
DESCRIPTION:Ever since the Cambrian explosion\, the efficient manipulation
  and sensing of light became ubiquitous in the living world\, and indeed c
 ritical for survival of most organisms. Concurrently\, optical technologie
 s are omnipresent in modern everyday live\, from free-space and cable comm
 unication to medical applications\, home appliances etc. Conventional opti
 cal elements such as lenses\, mirrors\, and polarization filters are made 
 from natural materials such as dielectrics\, metals\, and liquid crystals.
  These are typically bulky and energy inefficient\, and nature has therefo
 re developed nanostructured geometries assembled of two or more dielectri
 c materials. Only in the past 30 years\, we have started to copy natures b
 lueprints through bio-mimicry\, and developed our own nano-structured mate
 rials in the form of so-called photonic crystals and metamaterials.\n&nbsp
 \;\nThrough inverse engineering and machine learning\, photonic materials 
 have now\, for example\, been designed for analog computing and flat optic
 s\, with a metalens built into the next generation of the iPad and the iPh
 one. While inverse engineering and optical simulations are very useful too
 ls\, they do not reveal the fundamental reason for a designed optical mate
 rial response. I here instead follow an approach that classifies ordered n
 ano-structured materials according to their symmetry and associated topolo
 gy to predict an optical response based on first principles.\nThis approac
 h can lead to generic design principles and help to understand otherwise c
 ounter-intuitive behaviour. The real-space connectedness determines\, for 
 example\, the optical response of metal geometries. This explains an unexp
 ected strong linear and circular dichroism in gyroid metamaterials that is
  highly sensitive to its surface termination[1]. It further gives rise to 
 so-called electron acoustic waves in metallic double-nets [2]\, for which 
 light has a longitudinal polarization\, reminiscent of an acoustic wave Fi
 g. 1c-d. A group theoretical classification bulk modes\, on the other hand
 \, explains the absence of chiro-optical properties in chiral media [3]. I
 n combination with a topological characterization\, this method provides a
  first principle route to topologically protected edge states in flat mate
 rials [4] that can be used for lasing and on-chip photonic circuitry [5]. 
 In 3D bulk materials\, it leads to the emergence to a topologically protec
 ted near-zero refractive index [6] that gives rise to strongly spatially c
 oherent states of light Fig. 1a-b.\nFigure 1: Two 3D materials designed by
  their symmetry and topological classification. A dielectric chiral cubic 
 SRC net (a) gives rise to topologically protected near-zero index behavior
  that leads to spatially coherent states of light. A dipolar point source 
 in a block of such a material therefore produces planewave-like emission s
 een from the electric field amplitude that is periodic within the structur
 e and has planar wavefronts outside (b). The interpenetrating metallic PCU
 C double-net morphology (c) acts similar to a non-interacting double-plas
 ma with electron that supports longitudinal electron acoustic\, which cann
 ot couple to vacuum radiation. A dipole source in a block of this material
  therefore produces light that is confined within the cube that acts like 
 a resonator\, as seen from the intensity heatmap in (d)
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