08-Oct-2021 - Georg-August-Universität Göttingen

Novel quantum effect discovered in naturally occurring graphene

International research team finds atomically-thin carbon generates its own magnetic field

Usually, the electrical resistance of a material depends very much on its physical dimensions and fundamental properties. Under special circumstances, however, this resistance can adopt a fixed value that is independent of the basic material properties and “quantised” (meaning that it changes in discrete steps rather than continuously). This quantisation of electrical resistance normally occurs within strong magnetic fields and at very low temperatures when electrons move in a two-dimensional fashion. Now, a research team led by the University of Göttingen has succeeded in demonstrating this effect at low temperatures in the almost complete absence of a magnetic field in naturally occurring double-layer graphene, which is just two atoms thick. The results of the study have been published in Nature.

The team from the University of Göttingen, Ludwig Maximilian University of Munich and the University of Texas (Dallas) used two-layer graphene in its natural form. The delicate graphene flakes are contacted using standard microfabrication techniques and the flake is positioned so that it is hangs freely like a bridge, held at the edges by two metal contacts. The extremely clean double-layers of graphene show a quantisation of electrical resistance at low temperatures and almost undetectable magnetic fields. In addition, the electrical current flows without any loss of energy. The reason for this is a form of magnetism that is not generated in the usual way as seen in conventional magnets (ie by the alignment of the intrinsic magnetic moments of electrons), but by the motion of the charged particles in the graphene double layer itself. "In other words, the particles generate their own intrinsic magnetic field, which leads to the quantisation of the electrical resistance," says Professor Thomas Weitz from the University of Göttingen.

The reason this effect is special, is not just that it only requires an electric field, but also that it occurs in eight different versions that can be controlled by applied magnetic and electric fields. This results in a high degree of control, because the effect can be switched on and off and the direction of movement of the charged particles can be reversed. "This makes it a really interesting candidate for potential applications, for example, in the development of innovative computer components in the field of spintronics, which could have implications for data storage," says Weitz. "In addition, it is an advantage that we can show this effect in a system comprising a simple and naturally occurring material. This is in stark contrast to the recently popularised ‘heterostructures’, which require a complex and precise composition of different materials."


First, however, the effect must be further investigated and ways to stabilize it at higher temperatures need to be found, because currently it only occurs at up to five degrees above absolute zero (the latter being 273 degrees below 0oC).”

Facts, background information, dossiers
  • quantum effects
More about Uni Göttingen
  • News

    How diphosphorus can be used for chemical reactions

    Chemical syntheses of new active ingredients or functional materials are based on the use of molecular building blocks. These must be simultaneously reactive but also stable enough to enable targeted incorporation into larger molecules. A research team from the University of Göttingen and t ... more

    Eco-friendly plastic from cellulose and water

    Plastics offer many benefits to society and are widely used in our daily life: they are lightweight, cheap and adaptable. However, the production, processing and disposal of plastics are simply not sustainable, and pose a major global threat to the environment and human health. Eco-friendly ... more

    High-resolution microscope built from LEGO and bits of phone

    Microscopy is an essential tool in many fields of science and medicine. However, many groups have limited access to this technology due to its cost and fragility. Now, researchers from the Universities of Göttingen and Münster have succeeded in building a high-resolution microscope using no ... more

More about LMU
  • News

    Energy transmission by gold nanoparticles coupled to DNA structures

    Since the inception of the field in 2006, laboratories around the world have been exploring the use of ‘DNA origami’ for the assembly of complex nanostructures. The method is based on DNA strands with defined sequences that interact via localized base pairing. “With the aid of short strands ... more

    Did Darwinian evolution begin before life itself?

    Before life emerged on Earth, many physicochemical processes on our planet were highly chaotic. A plethora of small compounds, and polymers of varying lengths, made up of subunits (such as the bases found in DNA and RNA), were present in every conceivable combination. Before life-like chemi ... more

    Fluorescence microscopy at highest spatial and temporal resolution

    Only a few years ago, an ostensibly fundamental resolution limit in optical microscopy was superseded - a breakthrough which in 2014 led to the Nobel Prize in Chemistry for super-resolution microscopy. Since then, there has been another quantum leap in this area, which has further reduced t ... more

More about University of Texas at Dallas
  • News

    Researchers create powerful unipolar carbon nanotube muscles

    For more than 15 years, researchers at The University of Texas at Dallas and their collaborators in the U.S., Australia, South Korea and China have fabricated artificial muscles by twisting and coiling carbon nanotube or polymer yarns. When thermally powered, these muscles actuate by contra ... more

    Strong, super-tough carbon sheets made at low temperature

    An international research team led by scientists at Beihang University in China and The University of Texas at Dallas has developed high-strength, super-tough sheets of carbon that can be inexpensively fabricated at low temperatures. The team made the sheets by chemically stitching together ... more

    Charging ahead to develop better batteries

    Cellphones go dark during important conversations because a battery hasn't been recharged. Or the automotive industry revs up with excitement for a new battery-powered vehicle, but it needs frequent recharging. Or yardwork is delayed because the battery for your string trimmer is dead. Rese ... more