Potential for security technology through nano-SQUID-on-tip sensors
A team from the Weizmann Institute of Science in Rechovot has used a novel superconducting quantum sensor to visualise previously unknown magnetisation textures in rhombohedral graphene. Their findings, published in Nature Physics, show how electrons in multilayer graphene arrange themselves into complex, direction-dependent magnetic patterns. They used a nanoscale superconducting quantum interference device – a so-called nano-SQUID-on-tip sensor – mounted on the tip of an extremely fine pipette. This device can detect magnetic field strengths in the range of a few nanotesla, providing researchers with a unique tool for analysing local magnetic phenomena in 2D materials.
The scientists investigated how four isospin variants – combinations of spin and valley states – arrange themselves in rhombohedral multilayer graphene at low temperatures without an external magnetic field. Two distinct magnetic phases emerged: a spin-polarised semimetallic phase and a spin-valley-polarised quarter-metallic phase. By precisely mapping these structures, the researchers were able to draw conclusions about the strength of electron-electron interactions, in particular the so-called Hund’s exchange coupling, a quantity that had previously been virtually inaccessible to experiment.
This fundamental work not only opens up new insights into the quantum physics of graphene, but also points to promising applications in security technology. Nano-SQUID-on-tip technology allows the detection of extremely weak magnetic signals with nanometre-scale spatial resolution – a potential that extends far beyond materials research.
In the future, such sensors could be used in security and surveillance technology to detect magnetic signatures and manipulations with unprecedented precision. For example, forgery-proof magnetic codes in documents or components could be read, covert electronic manipulations detected, or forensic analyses performed at the microscopic level. This technology could also set new standards in the field of non-invasive material testing or in miniature sensors for drones and robotics.
The combination of 2D materials such as graphene and ultra-sensitive quantum sensor technology thus creates a new class of detection systems that have revolutionary potential in both basic research and practical security technology. In future, nano-SQUID-on-tip sensors could be used where conventional magnetic field sensors reach their limits – for example, in the detection of the slightest magnetic changes that indicate counterfeiting, sabotage or hidden electronic structures.
