Scientists apply 'twistronics' to light propagation and make a
breakthrough discovery
Promising pathway for leapfrog advancement in imaging, optical-computing technologies, biosensing and more

Date:
June 11, 2020
Source:
Advanced Science Research Center, GC/CUNY
Summary:
A research team has employed ''twistronics'' concepts (the science
of layering and twisting two-dimensional materials to control
their electrical properties) to manipulate the flow of light in
extreme ways.

The findings hold the promise for leapfrog advances in a variety
of light-driven technologies, including nano-imaging devices;
high-speed, low-energy optical computers; and biosensors.



FULL STORY ==========================================================================
A research team led by scientists at the Advanced Science Research
Center at The Graduate Center, CUNY (CUNY ASRC), in collaboration with
National University of Singapore, University of Texas at Austin and Monash University, has employed "twistronics" concepts (the science of layering
and twisting two- dimensional materials to control their electrical
properties) to manipulate the flow of light in extreme ways. The findings, published in the journal Nature, hold the promise for leapfrog advances
in a variety of light-driven technologies, including nano-imaging devices; high-speed, low-energy optical computers; and biosensors.


==========================================================================
The team took inspiration from the recent discovery of superconductivity
in a pair of stacked graphene layers that were rotated to the "magic
twist angle" of 1.1 degrees. In this configuration, electrons flow with
no resistance.

Separately, each graphene layer shows no special electrical
properties. The discovery has shown how the careful control of rotational symmetries can unveil unexpected material responses.

The research team discovered that an analogous principle can be applied
to manipulate light in highly unusual ways. At a specific rotation angle between two ultrathin layers of molybdenum trioxide, the researchers were
able to prevent optical diffraction and enable robust light propagation
in a tightly focused beam at desired wavelengths.

Typically, light radiated from a small emitter placed over a flat surface expands away in circles very much like the waves excited by a stone
that falls into a pond. In their experiments, the researchers stacked
two thin sheets of molybdenum trioxide -- a material typically used
in chemical processes -- and rotated one of the layers with respect to
the other. When the materials were excited by a tiny optical emitter,
they observed widely controllable light emission over the surface as
the rotation angle was varied. In particular, they showed that at the
photonic magical twist angle the configured bilayer supports robust, diffraction-free light propagation in tightly focused channel beams over
a wide range of wavelengths.

"While photons -- the quanta of light -- have very different
physical properties than electrons, we have been intrigued by the
emerging discovery of twistronics, and have been wondering if twisted two-dimensional materials may also provide unusual transport properties
for light, to benefit photon-based technologies," said Andrea Alu`,
founding director of the CUNY ASRC's Photonics Initiative and Einstein Professor of Physics at The Graduate Center. "To unveil this phenomenon,
we used thin layers of molybdenum trioxide. By stacking two of such
layers on top of each other and controlling their relative rotation, we
have observed dramatic control of the light guiding properties. At the
photonic magic angle, light does not diffract, and it propagates very
confined along straight lines. This is an ideal feature for nanoscience
and photonic technologies." "Our discovery was based on quite a specific material and wavelength range, but with advanced nanofabrication we
can pattern many other material platforms to replicate these unusual
optical features over a wide range of light wavelengths," said National University of Singapore (NUS) graduate student Guangwei Hu, who is first
author of the study and a long-term visiting researcher with Alu`'s
group. "Our study shows that twistronics for photons can open truly
exciting opportunities for light-based technologies, and we are excited
to continue exploring these opportunities," said Prof. C.W. Qiu, Mr.

Hu's co-advisor at NUS.


========================================================================== Story Source: Materials provided by
Advanced_Science_Research_Center,_GC/CUNY. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Guangwei Hu, Qingdong Ou, Guangyuan Si, Yingjie Wu, Jing Wu,
Zhigao Dai,
Alex Krasnok, Yarden Mazor, Qing Zhang, Qiaoliang Bao, Cheng-Wei
Qiu, Andrea Alu`. Topological polaritons and photonic magic angles
in twisted a-MoO3 bilayers. Nature, 2020; 582 (7811): 209 DOI:
10.1038/s41586-020- 2359-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200611094142.htm

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