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Physicists used graphs to build an extremely small magnetic field detector

Often times, it’s the smallest scientific measurements that matter most, and researchers have developed a new, super-tiny device that can detect magnetic fields even when they are extremely weak.

The device, a novel superconducting quantum interference device (SQUID), is only 10 nanometers high, or about a thousandth the thickness of a human hair. It consists of two layers of graphene, making it one of the smallest SQUIDs ever built – separated by a very thin layer of boron nitride.

Already used in fields as diverse as medicine and geology, these fascinating devices effectively make electrons work as quantum bits. This latest SQUID design should make the tiny instruments even more useful to scientists as they can detect very weak magnetic fields.

“Our new SQUID consists of a complex, six-layer stack of individual two-dimensional materials,”

; says physicist David Indolese from the University of Basel in Switzerland.

small squid 2A conventional SQUID (left) and the new SQUID (right). (University of Basel, Department of Physics)

“If two superconducting contacts are connected to this sandwich, it behaves like a SQUID – which means that extremely weak magnetic fields can be detected with it.”

Conventional SQUIDs work as a ring – a superconducting loop with two weak points. By analyzing the movement of electrons around this loop and the threshold at which the SQUID ceases to be a superconductor, magnetic fields can be measured.

While these devices can already detect weak magnetic fields, the size of the weak links is a limitation. By switching to a stacked design instead of a loop, the team behind the new SQUID can see magnetic fields that are even weaker.

One possible, albeit more technical, application of SQUIDs is to take a close look at topological insulators: materials that act as insulators, but can also have electrons that move across their surface.

“With the new SQUID we can determine whether these loss-free supercurrents can be traced back to the topological properties of a material and thus differentiate them from non-topological materials,” says the physicist Christian Sch√∂nenberger from the University of Basel.

SQUIDs are important wherever magnetic fields have to be measured: for example, when monitoring heart or brain activity or when detecting differences in the composition of rocks. Now these measurements can be even more accurate.

This is not going to be the latest SQUID-related innovation we see. Scientists are experimenting with different types of materials and nanostructures to make the devices smaller and more accurate than ever before.

In the meantime, the tiny SQUID described in this study can be used. Scientists can change their sensitivity by adjusting the distance between the two layers of graphene and adjusting the current passed through them. We are already looking forward to the discoveries it will lead to.

The research was published in Nano letters.

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