Illustration of local anodic oxidation of graphene
Illustration of local anodic oxidation of graphene

Ultra-clean graphene controls electronic transport in Quantum Hall effect

The quantum Hall effect, observed in two-dimensional electron systems when subjected to low temperatures and strong magnetic fields, plays a crucial role for the development of new two-dimensional electron systems in general, and for graphene-based 2D materials in particular. In order to understand this phenomenon, a fundamental understanding of the resistance of graphene in high magnetic fields as a function of temperature is required.

A team of researchers from the Istituto Nanoscienze-CNR in Pisa, the University of Salamanca, RWTH Aachen University, HFML-FELIX and the Institute for Molecules and Materials (IMM) have now discovered how the electronic transport in the quantum Hall regime of ultra-clean graphene is governed predominantly by electron-phonon scattering, i.e. scattering of electrons with thermally excited lattice vibrations. It enables extending the well-accepted notion of phonon-limited resistivity in ultra-clean graphene from zero magnetic field to the quantum Hall regime and works towards an understanding of the mysterious room-temperature quantum Hall effect in graphene. The results have recently been published in Nature Communications.

Ultra-clean graphene

There are still many unknowns on  the room temperature quantum Hall effect discovered in Nijmegen in 2007 and ultra-clean graphene devices are required to resolve this mystery.

The interdisciplinary team of researchers demonstrated that graphene encapsulated in hexagonal boron nitride (hBN) realizes a novel transport regime, where dissipation in the QH phase is governed predominantly by electron-phonon scattering, i.e. scattering of electrons with thermally excited lattice vibrations (and not by impurity scattering as in “dirty” systems). For this, the team used ultra-clean graphene and very high magnetic fields. “Our colleagues in Salamanca and Aachen  have made ultra-clean graphene devices (graphene on BN) and have come to Nijmegen to measure their resistance as a function of temperature (4 .. 300 K) and magnetic field (0 .. 35 T)”, professor Zeitler says.

Quantum Hall effect

The Quantum Hall effect (QHE), one of the most fundamental effects in 2D systems with three Nobel Prizes associated to it, is a well-accepted concept in physics describing the behaviour of 2D electrons in a magnetic. Apart from its significance for fundamental physics, it also establishes a standard on how to precisely define electrical resistance.

The current studies represent a combined experimental and theoretical approach to understand the quantum Hall effect in graphene at elevated temperatures. “Experiments have shown that for very strong magnetic fields applied to 2D systems, the Hall resistance becomes quantized, RH = h/ne2 and only depends on the charge of the electron and Planck’s constant, two fundamental constants of nature. However, normally one requires rather low temperatures, a few degrees above absolute zero, to observe it”, Zeitler explains.  “With our present work we can now pinpoint the behaviour of the QHE in graphene as a function of temperature and its robustness at elevated temperatures to electron-phonon scattering as we are used to explaining electronic transport without a magnetic field”.


Further studies

The Quantum Hall effect is used for an accurate calibration of resistances. Extending its applicability to higher temperature could revolutionise this quantum metrology and its application as a resistance standard. Additional experiments, such as further studies of the robustness of the QHE at elevated temperatures,  and extending the theoretical framework are already in progress.

Teamwork in IMM

The project is a combination of theoretical and experimental research of IMM scientists and their European partners with Dr. Sergio Pezzini, former post-doc at HMFL-FELX and now staff scientist at the Istituto Nanoscienze-CNR in Pisa, Italy as the driving force. Professor Katsnelson from the research group Theory of Condensed Matter was actively participating in theoretical studies of graphene from the very discovery of graphene in 2004. It was suggested him long ago that deviations of graphene from flatness (that is, ripples) provide one of the main sources of scattering for electrons and determine the physical picture of electronic transport in graphene both with and without magnetic field. However, when ripples are suppressed by using atomically flat boron nitride as a substrate, the electron-phonon scattering turns out to be the main scattering mechanism.

Now the experiments by dr. Pezzini, professor Zeitler, dr. Wiedmann and their co-workers performed within the HFML-FELIX lab using the very high static magnetic fields give a clear confirmation of this picture. This opens a way to explain the uniqueness of graphene which remains the only known material demonstrating QHE at room temperature. Professor Zeitler expertise is in semiconductors and nanostructures in high magnetic fields and professor Katsnelson is expert on theoretical solid-state physics and many-body quantum physics. Both groups are part of IMM. The research results have been published in the Nature Communications publication entitled ‘Phonon-mediated room-temperature quantum Hall transport in graphene’. “We are very pleased with the results of this research project which we discussed for many years, and now, at last, it turns out to be possible to fulfil it”, Zeitler and Katsnelson say.


At HFML-FELIX, high magnetic fields and intense (far) infrared free electron lasers are designed and used to investigate the properties and functionality of molecules and materials, realize fundamental scientific breakthroughs and tackle societal challenges in the areas of health, energy and smart materials. HFML-FELIX is scientifically embedded in the Institute for Molecules and Materials (IMM) within the Faculty of Science at Radboud University. (Bio)chemists, physicists, theorists and experimentalists, work closely together to unravel and control the functioning of molecules and materials at the smallest length and time scales.

Properties of condensed matter

The Theory of Condensed Matter group aims to predict structural and electronic properties of solid-state systems, from graphene and atomically-thin 2D materials to strongly correlated and magnetic materials. The group utilizes and develops advanced mathematical frameworks and state-of-the-art numerical approaches including quantum field theory, neural network and machine learning concepts, ab-initio calculations, and combinations.

Article information

Phonon-mediated room-temperature quantum Hall transport in graphene
Daniel Vaquero, Vito Clericò, Michael Schmitz, Juan Antonio Delgado-Notario, Adrian Martín-Ramos, Juan Salvador-Sánchez, Claudius S. A. Müller, Km Rubi, Kenji Watanabe, Takashi Taniguchi, Bernd Beschoten, Christoph Stampfer, Enrique Diez, Mikhail I. Katsnelson, Uli Zeitler, Steffen Wiedmann & Sergio Pezzini
Nature Communications, volume 14, 318 (2023) 
Phonon-mediated room-temperature quantum Hall transport in graphene | Nature Communications

Contact information

IMM Communications: imm-communication [at] (imm-communication[at]ru[dot]nl)