Regensburg 2000 – scientific programme

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SYNA: Carbon Nanotubes

SYNA III: HV III

SYNA III.1: Invited Talk

Thursday, March 30, 2000, 11:00–11:30, H20

Electric Properties of Multiwalled Carbon Nanotubes — •Christian Schönenberger — University of Basel, Institute of Physics, CH-4056 Basel, Switzerland

Metallic single-wall carbon nanotubes are believed to be ideal one-dimensional (1D) conductors. For example, ballistic transport over micrometer distances has been claimed. More recently, striking evidence for Luttinger liquid behavior has been observed. In contrast to these studies we have concentrated our research on multi-walled carbon nanotubes (MWNTs). In MWNTs one may expect several graphitic tubes to contribute to the conductance, so that it is tempting to place MWNTs at the border of 1D to higher-dimensional transport. However, low temperature studies show that the majority of charge is transported through one or a few shells only. Moreover, magnetotransport shows that the low-temperature resistance is dominated by interference and interaction effects. Surprisingly, we have also observed clear signatures disagreeing with conventional Fermi liquid theory, but which may be explained by Luttinger liquid theory. According to this theory, the conductance deviates from its ideal quantized value by a temperature dependent term which follows a power law with exponent p in the weak backscattering limit. We find values for p in the range of 0.1-0.3. Secondly, the conductance fluctuations which are induced by sweeping the back gate follow a power law as a function of temperature, too. Agreement with the conventional theory of universal conductance fluctuations (UCF) is only obtained in the limit of very long nanotubes. Finally, there is a pronounced suppression in the tunneling density-of-states, which again can be described by a power law in temperature and voltage. These results seem to indicate that Luttinger liquid behavior is even present in MWNTs. This may be considered as a surprise because all our magnetotransport measurements can be explained by traditional single particle theories.

This work is a collaboration between the Institute of Physics at Basel and the Institut de Génie Atomique of the ETH-Lausanne (EPFL). I acknowledge contributions from A. Bachtold, M. Buitelaar, C. Strunk, Th. Nussbaumer, J.-P. Salvetat (EPFL), J.-M. Bonard (EPFL), L. Forro (EPFL) and R. Egger (Freiburg).