A tiny instrument to measure the faintest magnetic fields

Date:
September 8, 2020
Source:
Swiss Nanoscience Institute, University of Basel
Summary:
Physicists have developed a minuscule instrument able to
detect extremely faint magnetic fields. At the heart of the
superconducting quantum interference device are two atomically
thin layers of graphene, which the researchers combined with boron
nitride. Instruments like this one have applications in areas such
as medicine, besides being used to research new materials.



FULL STORY ========================================================================== Physicists at the University of Basel have developed a minuscule
instrument able to detect extremely faint magnetic fields. At the heart
of the superconducting quantum interference device are two atomically
thin layers of graphene, which the researchers combined with boron
nitride. Instruments like this one have applications in areas such as
medicine, besides being used to research new materials.


==========================================================================
To measure very small magnetic fields, researchers often use
superconducting quantum interference devices, or SQUIDs. In medicine,
their uses include monitoring brain or heart activity, for example,
while in the earth sciences researchers use SQUIDs to characterize the composition of rocks or detect groundwater flows. The devices also have
a broad range of uses in other applied fields and basic research.

The team led by Professor Christian Scho"nenberger of the University of
Basel's Department of Physics and the Swiss Nanoscience Institute has
now succeeded in creating one of the smallest SQUIDs ever built. The researchers described their achievement in the scientific journal Nano
Letters.

A superconducting ring with weak links A typical SQUID consists of a superconducting ring interrupted at two points by an extremely thin film
with normal conducting or insulating properties. These points, known
as weak links, must be so thin that the electron pairs responsible for superconductivity are able to tunnel through them. Researchers recently
also began using nanomaterials such as nanotubes, nanowires or graphene
to fashion the weak links connecting the two superconductors.

As a result of their configuration, SQUIDs have a critical current
threshold above which the resistance-free superconductor becomes a
conductor with ordinary resistance. This critical threshold is determined
by the magnetic flux passing through the ring. By measuring this critical current precisely, the researchers can draw conclusions about the strength
of the magnetic field.



========================================================================== SQUIDs with six layers "Our novel SQUID consists of a complex, six-layer
stack of individual two- dimensional materials," explains lead author
David Indolese. Inside it are two graphene monolayers separated by a
very thin layer of insulating boron nitride.

"If two superconducting contacts are connected to this sandwich, it
behaves like a SQUID -- meaning it can be used to detect extremely weak magnetic fields." In this setup, the graphene layers are the weak links, although in contrast to a regular SQUID they are not positioned next
to each other, but one on top of the other, aligned horizontally. "As
a result, our SQUID has a very small surface area, limited only by
the constraints of nanofabrication technology," explains Dr. Paritosh
Karnatak from Scho"nenberger's team.

The tiny device for measuring magnetic fields is only around 10
nanometers high -- roughly a thousandth of the thickness of a human
hair. The instrument can trigger supercurrents that flow in minuscule
spaces. Moreover, its sensitivity can be adjusted by changing the
distance between the graphene layers. With the help of electrical fields,
the researchers are also able to increase the signal strength, further enhancing the measurement accuracy.

Analyzing topological insulators The Basel research team's primary goal
in developing the novel SQUIDs was to analyze the edge currents of
topological insulators. Topological insulators are currently a focus
of countless research groups all over the world. On the inside, they
behave like insulators, while on the outside -- or along the edges --
they conduct current almost losslessly, making them possible candidates
for a broad range of applications in the field of electronics.

"With the new SQUID, we can determine whether these lossless supercurrents
are due to a material's topological properties, and thereby tell
them apart from non-topological materials. This is very important for
the study of topological insulators," remarked Scho"nenberger of the
project. In future, SQUIDs could also be used as low-noise amplifiers
for high-frequency electrical signals, or for instance to detect local brainwaves (magnetoencephalography), as their compact design means a
large number of the devices can be connected in series.

The paper is the outcome of close collaboration among groups at the
University of Basel, the University of Budapest and the National Institute
for Material Science in Tsukuba (Japan).


========================================================================== Story Source: Materials provided by Swiss_Nanoscience_Institute,_University_of_Basel. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. David I. Indolese, Paritosh Karnatak, Artem Kononov, Raphae"lle
Delagrange, Roy Haller, Lujun Wang, Pe'ter Makk, Kenji Watanabe,
Takashi Taniguchi, Christian Scho"nenberger. Compact SQUID Realized
in a Double- Layer Graphene Heterostructure. Nano Letters, 2020;
DOI: 10.1021/ acs.nanolett.0c02412 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200908093746.htm

--- up 2 weeks, 1 day, 6 hours, 50 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)