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Physicists used graphene to build an extremely small magnetic field detector

Often it is the tiniest scientific measurements that are most important, and researchers have developed a new super small device that can detect magnetic fields even when they are extremely weak.

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

These fascinating devices are already being used in fields as diverse as medicine and geology and effectively make electrons work like quantum bits. This latest SQUID project is expected to make the tiny tools even more useful to scientists, thanks to its ability to detect very weak magnetic fields.

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

; says physicist David Indolese of 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 it can be used to detect extremely weak magnetic fields.”

Conventional SQUIDs function like a ring, a superconducting circuit that has two “weak link” points. By analyzing the travel of electrons around this ring and the threshold at which the SQUID stops being a superconductor, it is possible to measure magnetic fields.

Although these devices are already capable of detecting weak magnetic fields, the size of the weak links is a limitation. By switching to a stacked design, rather than a loop, the team behind the new SQUID can detect even weaker magnetic fields.

One possible, albeit rather technical, application of SQUIDs is to look closely at topological insulators: materials that act as insulators, but which can also have electrons traveling on their surface.

“With the new SQUID, we can determine whether these lossless supercurrents are due to the topological properties of a material, and thus distinguish them from non-topological materials,” says physicist Christian Sch√∂nenberger of the University of Basel.

Wherever magnetic fields need to be measured, SQUIDs are important: in monitoring heart or brain activity, for example, or detecting differences in rock composition. Now, those measurements can be even more accurate.

This won’t be the last 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.

Meanwhile, the tiny SQUID outlined in this study is ready to be deployed. Scientists are able to modify its sensitivity by adjusting the distance between the two layers of graphene and changing the current flowing through it. We are already looking forward to the breakthroughs it will lead to.

The research was published in Nano Letters.

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