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First Experimental Observation of Weyl Points

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Weyl
particles – massless particles linearly dispersing in all three dimensions (3D)
-- were first theorized by Hermann
Weyl in
1929, who found such a
solution to
the Dirac equation proposed by Paul Dirac in 1928. A material hosting
Weyl
particles
features
singular
points
in its dispersion
relations – the Weyl
points.
Weyl
points are 3D
upgrades of
the 2D Dirac points in graphene,
the proposal of which led to a
Nobel
prize
in
Physics
in
2010.
However,
there has
been
no observation of the
Weyl points (particles) until 2015.


In 2015, MIT
MRSEC
researchers
have
experimentally observed that photons
propagating inside
a specially-designed 3D photonic crystal behave the same way as the long-sought
Weyl
particles. This realization is based on their own theoretical work two years
ago, proposing
Weyl points in the band
structure
of a gyroid
photonic crystal. With the help from MIT Central Machine Shop, the team
fabricated an inversion-breaking double-
gyroid
photonic crystal at the microwave frequency
(Figure A). They
then characterized the bulk photon
dispersions of
the crystal using angle-resolved transmission, working with their
collaborators
in
Zhejiang University in China. The transmission results
reveal
the
Weyl
dispersions matching the theoretical results
(Figure
B).
Since
Weyl
points are unique topological monopoles in the momentum space, this work also
paves the way to a variety of opportunities of topological photonics in three
dimensions.

Comparison between the experimental and theoretical results. The bulk transmission data matches the predicted Weyl dispersions.

 

Comparison between the experimental and theoretical results. The bulk transmission data matches the predicted Weyl dispersions.