Researchers find topological phenomena at high, technologically relevant frequencies

Date:
March 30, 2022
Source:
University of Pennsylvania
Summary:
A new study describes topological control capabilities in an
acoustic system at high technologically relevant frequencies. This
work has implications for applications such as 5G communications
and quantum information processing.



FULL STORY ==========================================================================
New research published in Nature Electronics describes topological
control capabilities in an integrated acoustic-electronic system at technologically relevant frequencies. This work paves the way for
additional research on topological properties in devices that use high-frequency sound waves, with potential applications including 5G communications and quantum information processing. The study was led by
Qicheng (Scott) Zhang, a postdoc in the lab of Charlie Johnson at the University of Pennsylvania, in collaboration with the group of Bo Zhen
and colleagues from Beijing University of Posts and Telecommunications
and the University of Texas at Austin.


==========================================================================
This research builds on concepts from the field of topological materials,
a theoretical framework developed by Penn's Charlie Kane and Eugene
Mele. One example of this type of material is a topological insulator,
which acts as an electrical insulator on the inside but has a surface
that conducts electricity.

Topological phenomena are hypothesized to occur in a wide range of
materials, including those that use light or sound waves instead of electricity.

In this study, Zhang was interested in studying topological phononic
crystals, metamaterials that use acoustic waves, or phonons. In these
crystals, topological properties are known to exist at low frequencies
in the megahertz range, but Zhang wanted to see if topological phenomena
might also occur at higher frequencies in the gigahertz range because of
the importance of these frequencies for telecommunication applications
such as 5G.

To study this complex system, the researchers combined state-of-the-art methodologies and expertise across theory, simulation, nanofabrication,
and experimental measurements. First, researchers in the Zhen lab,
who have expertise in studying topological properties in light waves,
conducted simulations to determine the best types of devices to
fabricate. Then, based on the results of the simulations and using high-precision tools at Penn's Singh Center for Nanotechnology,
the researchers etched nanoscale circuits onto aluminum nitride
membranes. These devices were then shipped to the lab of Keji Lai at
UT Austin for microwave impedance microscopy, a method that captures high-resolution images of the acoustic waves at incredibly small
scales. Lai's approach uses a commercial atomic force microscope with modifications and additional electronics developed by his lab.

"Before this, if people want to see what's going on in these materials,
they usually need to go to a national lab and use X-rays," Lai says. "It's
very tedious, time consuming, and expensive. But in my lab, it's just
a tabletop setup, and we measure a sample in about 10 minutes, and the sensitivity and resolution are better than before." The key finding of
this work is the experimental evidence showing that topological phenomena
do in fact occur at higher frequency ranges. "This work brings the concept
of topology to gigahertz acoustic waves," says Zhang. "We demonstrated
that we can have this interesting physics at a useful range, and now
we can build up the platform for more interesting research to come."
Another important result is that these properties can be built into the
atomic structure of the device so that different areas of the material
can propagate signals in unique ways, results that were predicted by
theorists but were "amazing" to see experimentally, says Johnson. "That
also has its own important implications: When you're conveying a wave
along a sharp trail in ordinary systems that don't have these topological effect, at every sharp turn you're going to lose something, like power,
but in this system you don't," he says.

Overall, the researchers say that this work provides a critical starting
point for progress in both fundamental physics research as well as for developing new devices and technologies. In the near term, the researchers
are interested in modifying their device to make it more user-friendly
and improving its performance at higher frequencies, including frequencies
that are used for applications such as quantum information processing.

"In terms of technological implications, this is something that could
make its way into the toolbox for 5G or beyond," says Johnson. "The basic technology we're working on is already in your phone, so the question
with topological vibrations is whether we can come up with a way to do something useful at these higher frequency ranges that are characteristic
of 5G."

========================================================================== Story Source: Materials provided by University_of_Pennsylvania. Original written by Erica K.

Brockmeier. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
* Perfectly_transmitted_topological_acoustic_wave ========================================================================== Journal Reference:
1. Qicheng Zhang, Daehun Lee, Lu Zheng, Xuejian Ma, Shawn I. Meyer,
Li He,
Han Ye, Ze Gong, Bo Zhen, Keji Lai, A. T. Charlie Johnson. Gigahertz
topological valley Hall effect in nanoelectromechanical
phononic crystals. Nature Electronics, 2022; 5 (3): 157 DOI:
10.1038/s41928-022- 00732-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220330103328.htm

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