On Manchester Universityscientists have reported a record high emerging magnetoresistance on graphene under ambient conditions.
This study is reported in the journal Natural on April 13thth2023.
Strong materials that can change their resistivity when subjected to a magnetic field are highly sought after for a variety of applications. For example, magnetic sensors are used in every car and computer, making such materials indispensable.
However, these materials are rare, and most metals and semiconductors show only slight changes in electrical resistivity at room temperature and practical magnetic fields (usually less than one millionth of 1%).
To observe a strong magnetoresistance response, scientists usually need to cool the material to the temperature of liquid helium to reduce electron scattering and enable cyclotron trajectory tracking.
Recently, a research group led by Professor Sir Andre Geim made an amazing discovery: good old graphene, which has been studied extensively over the last 20 years, shows a very strong response. It can reach over 100% in the magnetic field produced by standard permanent magnets (about 1,000 Gauss). This is a record-breaking magnetoresistivity for any known material.
People working on graphene like myself have always felt that this goldmine of physics should have run out long ago. Material constantly proves that we have found another incarnation wrong. Today I have to admit again that graphene is dead, graphene lives on for a long time.
Sir Andre Geim, Professor, University of Manchester
To achieve this, the scientists utilized high-quality graphene in its initial state, where only temperature-excited charge carriers were present.
This makes a fast-moving “Dirac fermion” plasma that exhibits unusually high mobility despite regular scattering. Therefore, the high neutrality and mobility of this Dirac plasma is known to be a vital component for the reported large magnetoresistance.
Over the past 10 years, the electronic quality of graphene devices has improved dramatically, and everyone seems to be focused on discovering new phenomena at the low temperature of liquid helium, ignoring what happens in ambient conditions.
Alexey Berdyugin, Study Corresponding Author, University of Manchester
Berdyugin added, “This may not be too surprising since the cooler your sample is, the more interesting the behavior will be. We decided to start a fire and suddenly a lot of unexpected phenomena appeared.”
Scientists have made an interesting discovery about neutral graphene: at high temperatures, it behaves like a “strange metal”, a material in which the scattering of electrons is determined solely by the Heisenberg uncertainty principle. This is in addition to the record breaking magnetoresistivity that has been observed.
The strange behavior of metals is still poorly understood, and scientists around the world are working to unravel this puzzle. Recent research from Manchester has added to the mystery by showing that graphene exhibits remarkable linear magnetoresistance in fields above a few Tesla, which is only slightly dependent on temperature. This high field magnetoresistance is completely unprecedented.
The phenomenon of linear magnetoresistance has been a mystery for more than a century since it was first observed. However, recent research from Manchester provides important clues about the origins of strange metal behavior and linear magnetoresistance.
It’s possible that the mystery surrounding the strange metal may finally be solved thanks to graphene. This material offers an electronic system that is clean, well-characterized, and relatively simple to learn.
High-quality undoped graphene at room temperature offers the opportunity to explore entirely new regimes that could in principle be discovered even a decade ago but have somehow been ignored by everyone else. We plan to study the regimes of these strange metals and, of course, more interesting results, phenomena and applications will follow.
Leonid Ponomarenko, Distinguished Author, University of Manchester
Xin, N., et al. (2023) Magnetoresistance of Dirac’s giant plasma in high-mobility graphene. Natural. doi.org/10.1038/s41586-023-05807-0.