Quantum transport in 2D materials

Two-dimensional van-der-Waals materials such as graphene serve as an extremely productive platform for investigating and discovering novel quantum phenomena. Of particular interest is the question of specifically controlling charge transport at cryogenic temperatures. This makes it possible to observe a variety of exotic topological and correlated effects, such as unconventional superconductivity. Our goal is to use these experiments to gain deeper insights into fundamental physical laws and to identify possible candidates for the next generation of classical and quantum computers. Accordingly, state-of-the-art methods such as electron beam lithography and near-field microscopy are also used to design, manufacture, and characterize the latest sample systems and devices.

The most important phenomena at a glance:

Conventional and unconventional superconductivity
Wigner crystals, charge density waves, and other correlated insulators
Integer quantum Hall effect and other topological insulators
Fractional quantum Hall effect and anyons

Further reading:

A. M. Seiler, F. R. Geisenhof, F. Winterer, K. Watanabe, T. Taniguchi, T. Xu, F. Zhang and R. T. Weitz, "Quantum cascade of correlated phases in trigonally warped bilayer graphene", Nature 608, 298–302 (2022) (article online)
F. R. Geisenhof, F. Winterer, A. M. Seiler, J. Lenz, I. Martin and R. T. Weitz, "Interplay between topological valley and quantum Hall edge transport", Nat. Commun. 13, 4187 (2022) (article online)
F. Winterer, A.M. Seiler, A. Ghazaryan, F.R. Geisenhof, K. Watanabe, T. Taniguchi, M. Serbyn and R. T. Weitz, "Spontaneous Gully Polarized Quantum Hall States in ABA Trilayer Graphene", Nano Lett. 22, 8, 3317–3322, (2022) (article online)
F. R. Geisenhof, F. Winterer, A. M. Seiler, J. Lenz, T. Xu, F. Zhang and R. T. Weitz, "Quantum anomalous Hall octet driven by orbital magnetism in bilayer graphene", Nature 598, 53-58 (2021) (article online)

Project funding and collaborations

Charge transport in organic semiconductors

Organic semiconductors are of interest for use in energy harvesting, for transistor circuits in large-area electronic devices and for neuromorphic low-energy electronics. In this context, the goal of our research is to add fundamental understanding of (opto-) electronic processes in organic materials. For example, despite the long history of research in organic semiconducting materials, there is still a debate about the prevailing charge transport mechanism and dissipation mechanisms. Via precisely controlling the morphology of organic small molecules and polymers, we aim to unravel the prevailing charge transport process occurring within organic semiconductors and across semiconductor heterojunctions.

Further reading:

J. Lenz, M. Statz, K. Watanabe, T. Taniguchi, F. Ortmann and R. T. Weitz, "Charge transport in single polymer fiber transistors in the sub 100 nm regime: temperature dependence and Coulomb blockade", J. Phy. Mater. 6, 015001 (2023) (article online)
L. S. Walter, A. Axt, J. W. Borchert, T. Kammerbauer, F. Winterer, J. Lenz, S. A. L. Weber and R. T. Weitz, "Revealing and Controlling Energy Barriers and Valleys at Grain Boundaries in Ultrathin Organic Films", Small 18, 2200605 (2022) (article online)
J. Lenz, F. del Giudice, F.R. Geisenhof, F. Winterer, R.T. Weitz, "Vertical, electrolyte-gated organic transistors: continuous operation in the MA/cm2 regime and use as low-power artificial synapses", Nat. Nanotechnol. 14, 579–585 (2019) (article online)
L.S. Schaffroth, J. Lenz, V. Geigold, M. Kögl, A. Hartschuh, R.T. Weitz, "Freely suspended, van-der-Waals bound organic nm-thin functional films: mechanical and electronic characterization", Adv. Mater. 31, 1808309 (2019), (article online)