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)
A. M. Seiler, M. Statz, C. Eckel, I. Weimer, J. F. Pöhls, K. Watanabe, T. Taniguchi, F. Zhang and R. T. Weitz, "Sliding Wigner crystals in bilayer graphene at zero and finite magnetic fields", arXiv:2408.16628 (2024) (article online)
F. Winterer, F. R. Geisenhof, N. Fernandez, A. M. Seiler, F. Zhang and R. T. Weitz, "Ferroelectric and anomalous quantum Hall states in intrinsic rhombohedral trilayer graphene", Nature Physics 20, 422-427 (2024) (article online)

Project funding and collaborations

Charge transport in organic semiconductors

Organic semiconductors are emerging as promising alternatives to conventional inorganic materials due to their unique physical and chemical properties, such as mechanical flexibility, tunability, and cost-effective processing. Despite intensive research over the past decades, a comprehensive understanding of their fundamental (opto-)electronic properties, particularly charge transport mechanisms, remains incomplete. Our research group is dedicated to addressing this challenge by fabricating novel organic devices and probing their intrinsic behaviors. To achieve this, we employ advanced experimental techniques, including Scanning Near-field Optical Microscopy (SNOM), Kelvin Probe Force Microscopy (KPFM), and probestation measurements, aiming to unveil new insights into organic electronic functionality.

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)