Physicists use graphene to make highly tiny magnetic field detectors

It is often the most important scientific measurement that is most important, and researchers have developed a new, super-small device capable of detecting magnetic fields, even when they are extremely faint.

The device is a new kind of superconducting quantum interference device (SQUID), which is just 10 nanometers high, or one thousandth of the thickness of a human hair. It is made from two layers of graphene – making it one of the smallest squares ever built – separated by a very thin layer of boron nitride.

These attractive devices are already used in fields as diverse as medicine and geology, and they effectively serve electrons as quantum bits. This latest SQUID design should make small devices even more useful to scientists, thanks to the ability to detect very weak magnetic fields.

“Our novel SQUID consists of a complex, six-layer stack of individual two-dimensional materials,” says physicist David Indolliz of the University of Basel, Switzerland.

A traditional SQUID (left) and new SQUID (right). (University of Basel, Department of Physics)

“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.”

Traditional SQUIDs function as a ring – a superconducting loop consisting of two ‘weak link’ points. By analyzing the travel of electrons around this loop, and the extent to which SQUID stops being a superconductor, magnetic fields can be measured.

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

The technical application of SQUIDs, if possible, is to take a closer look at topical insulators: materials that act as insulators, but in which electrons can also travel on their surface.

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

Anywhere magnetic fields need to be measured, SQUIDs are important: for example in monitoring the activity of the heart or brain, or in detecting differences in the structure of rocks. Now, those measurements can be even more accurate.

This will not be the latest SQUID-related innovation that we see. Scientists are experimenting with a wide variety of materials and nanostructures to obtain devices smaller and more accurately than ever before.

Meanwhile, the miniscule mentioned in this study is set to deploy. Scientists are able to change its sensitivity by adjusting the distance between two graphene layers and applying current through it. We are already looking forward to the discoveries that lead to it.

The research has been published in Nano letters.