Researchers from The University of Manchester announce record-high magnetoresistance in graphene under ambient conditions in a publication that was published in Nature this week (April 13, 2023).
Materials that significantly alter their resistivity in the presence of magnetic fields are highly desired for a variety of applications. For instance, every computer and car include a plethora of tiny magnetic sensors. These substances are uncommon, and the majority of metals and semiconductors very slightly alter their electrical resistivity at room temperature and at practically usable magnetic fields (usually by less than a millionth of 1%). Researchers typically cool materials to liquid-helium temperatures to allow electrons within to follow cyclotron trajectories and scatter less, allowing for the observation of a strong magnetoresistance response.
Now, a study team led by Professor Sir Andre Geim has discovered that good old graphene, which appeared to have been thoroughly investigated over the previous two decades, has an incredibly powerful response, reaching above 100% in magnetic fields of typical permanent magnets (of approximately 1,000 Gauss). In terms of all known materials, this is a record for magnetoresistivity.
Speaking about this latest graphene discovery, Sir Andre Geim said, “People working on graphene like myself always felt that this gold mine of physics should have been exhausted long ago. The material continuously proves us wrong finding yet another incarnation. Today I have to admit again that graphene is dead, long live graphene.”
The researchers tuned high-quality graphene to its intrinsic, virgin state, where there were only charge carriers excited by temperature, in order to accomplish this. This led to the formation of a plasma of swift Dirac fermions that, despite regular scattering, displayed a surpisingly high mobility. The claimed huge magnetoresistance is mostly due to the Dirac plasma’s great mobility and neutrality.
“Over the last 10 years, electronic quality of graphene devices has improved dramatically, and everyone seems to focus on finding new phenomena at low, liquid-helium temperatures, ignoring what happens under ambient conditions. This is perhaps not so surprising because the cooler your sample the more interesting its behavior usually becomes. We decided to turn the heat up and unexpectedly a whole wealth of unexpected phenomena turned up,” says co-author Dr. Alexey Berdyugin.
In addition to the record magnetoresistivity, the researchers have discovered that at high temperatures, neutral graphene transforms into a so-called “strange metal.” These materials are referred to as having fast electron scattering, which is solely determined by the Heisenberg uncertainty principle. Uncertainty surrounds the behaviour of unusual metals, which is still being investigated globally.
By demonstrating that graphene exhibits a massive linear magnetoresistance at fields over a few Tesla that is only faintly temperature dependent, the Manchester work furthers the mystique surrounding the field. This high-field magnetoresistance sets yet another record.
“Undoped high-quality graphene at room temperature offers an opportunity to explore an entirely new regime that in principle could be discovered even a decade ago but somehow was overlooked by everyone. We plan to study this strange-metal regime and, surely, more of interesting results, phenomena and applications will follow,” adds Dr. Leonid Ponomarenko, one of the authors.
