The strange metal behavior of magnetoresistance of graphene breaks record high

"The material continuously proves us wrong, finding yet another incarnation," said researcher Sir Andre Geim.
Loukia Papadopoulos
An illustration of graphene.jpg
An illustration of graphene.

Simfo/iStock 

Researchers from The University of Manchester have finally reported record-high magnetoresistance that appears in graphene under ambient conditions.

This according to a press release published on Wednesday by the institution.

A research team led by Professor Sir Andre Geim has found that good old graphene can reach a record-breaking above 100% in magnetic fields of standard permanent magnets (of about 1,000 Gauss).

“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,” Geim said in a press statement.

The researchers used high-quality graphene and tuned it to its intrinsic, virgin state where there were only charge carriers excited by temperature, creating a plasma of fast-moving “Dirac fermions.” 

“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,” said Dr Alexey Berdyugin, the corresponding author of the paper.

The researchers have also found that, at elevated temperatures, neutral graphene becomes a so-called “strange metal,” the name given to materials where electron scattering becomes ultimately fast, being determined only by the Heisenberg uncertainty principle. 

The phenomenon of linear magnetoresistance has puzzled scientists for more than a century since it was first observed. The current Manchester work provides important clues about the origins of the strange metal behavior and of the linear magnetoresistance. Perhaps, the mysteries can now be finally solved thanks to graphene as it represents a clean, well-characterized and relatively simple electronic system.

“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”, added Dr Leonid Ponomarenko, one of the leading paper authors. 

The paper was published in Nature this week.

Study abstract:

The most recognizable feature of graphene’s electronic spectrum is its Dirac point, around which interesting phenomena tend to cluster. At low temperatures, the intrinsic behavior in this regime is often obscured by charge inhomogeneity but thermal excitations can overcome the disorder at elevated temperatures and create an electron–hole plasma of Dirac fermions. The Dirac plasma has been found to exhibit unusual properties, including quantum-critical scattering and hydrodynamic flow. However, little is known about the plasma’s behavior in magnetic fields. Here we report magnetotransport in this quantum-critical regime. In low fields, the plasma exhibits giant parabolic magnetoresistivity reaching more than 100 per cent in a magnetic field of 0.1 tesla at room temperature. This is orders-of-magnitude higher than magnetoresistivity found in any other system at such temperatures. We show that this behavior is unique to monolayer graphene, being underpinned by its massless spectrum and ultrahigh mobility, despite frequent (Planckian limit) scattering. With the onset of Landau quantization in a magnetic field of a few tesla, where the electron–hole plasma resides entirely on the zeroth Landau level, giant linear magnetoresistivity emerges. It is nearly independent of temperature and can be suppressed by proximity screening, indicating a many-body origin. Clear parallels with magnetotransport in strange metals and so-called quantum linear magnetoresistance predicted for Weyl metals offer an interesting opportunity to further explore relevant physics using this well defined quantum-critical two-dimensional system.