Smooth sailing for electrons in graphene
Physicists directly measured, at nanometer resolution, the fluid-like
flow of electrons in graphene

Date:
February 17, 2023
Source:
University of Wisconsin-Madison
Summary:
Physicists have directly measured, for the first time at nanometer
resolution, the fluid-like flow of electrons in graphene. The
results have applications in developing new, low-resistance
materials, where electrical transport would be more efficient.


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FULL STORY ========================================================================== Physicists at the University of Wisconsin-Madison directly measured, for
the first time at nanometer resolution, the fluid-like flow of electrons
in graphene. The results, which will appear in the journal Science on
Feb. 17, have applications in developing new, low-resistance materials,
where electrical transport would be more efficient.


========================================================================== Graphene, an atom-thick sheet of carbon arranged in a honeycomb pattern,
is an especially pure electrical conductor, making it an ideal material
to study electron flow with very low resistance. Here, researchers intentionally added impurities at known distances and found that electron
flow changes from gas- like to fluid-like as temperatures rise.

"All conductive materials contain impurities and imperfections that block electron flow, which causes resistance. Historically, people have taken
a low- resolution approach to identifying where resistance comes from,"
says Zach Krebs, a physics graduate student at UW-Madison and co-lead
author of the study. "In this study, we image how charge flows around
an impurity and actually see how that impurity blocks current and causes resistance, which is something that hasn't been done before to distinguish gas-like and fluid-like electron flow.

The researchers intentionally introduced obstacles in the graphene,
spaced at controlled distances and then applied a current across the
sheet. Using a technique called scanning tunneling potentiomentry (STP),
they measured the voltage with nanometer resolution at all points on
the graphene, producing a 2D map of the electron flow pattern.

No matter the obstacle spacing, the drop in voltage through the channel
was much lower at higher temp (77 kelvins) vs lower temp (4 K), indicating lower resistance with more electrons passing through.

At temperatures near absolute zero, electrons in graphene behave like a
gas: they diffuse in all directions and are more likely to hit obstacles
than they are to interact with each other. Resistance is higher, and
electron flow is relatively inefficient. At higher temperatures -- 77 K,
or minus 196 C -- the fluid-like behavior of electron flow means they
are interacting with each other more than they are hitting obstacles,
flowing like water between two rocks in the middle of a stream. It is
as if the electrons are communicating information about the obstacle to
each other and diverting around the rocks.

"We did a quantitative analysis [of the voltage map] and found that at
the higher temperature, the resistance is much lower in the channel. The electrons were flowing more freely and fluid-like," Krebs says. "Graphene
is so clean that we're forcing the electrons to interact with each other
before they interact with anything else, and that is crucial in getting
them to behave like a fluid." Former UW-Madison graduate student Wyatt
Behn is a co-first author on this study conducted in physics professor
Victor Brar's group. Funding was provided by the U.S. Department of
Energy (DE-SC00020313), the Office of Naval Research (N00014-20-1-2356)
and the National Science Foundation (DMR-1653661).

* RELATED_TOPICS
o Matter_&_Energy
# Graphene # Nature_of_Water # Spintronics #
Inorganic_Chemistry # Materials_Science # Chemistry #
Physics # Engineering_and_Construction
* RELATED_TERMS
o Viscosity o Turbulence o Materials_science o Flow_measurement
o Aerodynamics o Carbon_nanotube o Pyroelectricity o
Drag_(physics)

========================================================================== Story Source: Materials provided by
University_of_Wisconsin-Madison. Original written by Sarah Perdue. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Zachary J. Krebs, Wyatt A. Behn, Songci Li, Keenan J. Smith, Kenji
Watanabe, Takashi Taniguchi, Alex Levchenko, Victor W. Brar. Imaging
the breaking of electrostatic dams in graphene for ballistic
and viscous fluids. Science, 2023; 379 (6633): 671 DOI:
10.1126/science.abm6073 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/02/230217081442.htm

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