About the topic
The recent technological advances in encapsulating graphene by hexagonal boron nitride forming artificial van-der-Waals heterostructures allows the fabrication of graphene devices with unique electronic properties. Outstanding charge carrier mobilities and mean free paths with more than 25 micrometer are now accessible making this material stack interesting for studying ballistic transport. By further structuring the graphene-hBN based heterostructures mesoscopic devices can be fabricated on which phase coherent ballistic quantum transport can be studied.
Here, I will present low-temperature magneto-transport measurements on both (i) graphene quantum point contacts (Fig.1) and (ii) high mobility graphene rings encapsulated in hexagonal boron nitride. Our experiments allow to extract information on quantized conductance, renormalized Fermi velocities close to the charge neutrality point as well as the co-existence of weak localization, Aharonov-Bohm (AB) oscillations and universal conductance fluctuations in graphene rings. In particular, I show signatures of magnetic focusing effects at small magnetic fields confirming ballistic transport in mesoscopic graphene devices and I report on the observation of the AB conductance oscillations in the quantum Hall regime at reasonable high magnetic fields, where we find regions with enhanced AB oscillation visibility with values up to 0.7%. These oscillations are well explained by taking disorder into account allowing for a coexistence of hard and soft-wall confinement.
About the speaker
Christoph Stampfer, born in 1977, is currently Professor at the 2nd Institute of Physics at the RWTH Aachen University. His primary interests include graphene and 2D materials research, mesoscopic transport, and micro electromechanical systems. He holds a Dipl.-Ing. Degree in Technical Physics from the TU Vienna and a PhD in Mechanical Engineering from the ETH Zurich. He was a staff member at the Institute for Micro and Nano Systems of the ETH Zurich from 2003 to 2007 and a postdoctoral fellow of the Institute for Solid State Physics (ETH Zurich) from 2007 to 2009.
From 2009 till 2013 he was JARA-FIT Junior Professor at the RWTH Aachen and the Forschungszentrum Jülich. He has been awarded with an ERC Starting Grant to work on « Graphene Quantum Electromechanical Systems » in 2011 and is member of the Young Scientist community of the World Economic Forum (WEF) since 2014.