1. Institut für Physik, Universität Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
2. Institut de Génie Atomique, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland

Correspondence to: Christian Schönenberger¹ Correspondence and requests for materials should be addressed to C.S. (e-mail: Email: Schonenberg@ubaclu.unibas.ch).

When electrons pass through a cylindrical electrical conductor aligned in a magnetic field, their wave-like nature manifests itself as a periodic oscillation in the electrical resistance as a function of the enclosed magnetic flux¹. This phenomenon reflects the dependence of the phase of the electron wave on the magnetic field, known as the Aharonov–Bohm effect², which causes a phase difference, and hence interference, between partial waves encircling the conductor in opposite directions. Such oscillations have been observed in micrometre-sized thin-walled metallic cylinders^{3, 4, 5} and lithographically fabricated rings^{6, 7, 8}. Carbon nanotubes^{9, 10} are composed of individual graphene sheets rolled into seamless hollow cylinders with diameters ranging from 1 nm to about 20 nm. They are able to act as conducting molecular wires^{11, 12, 13, 14, 15, 16, 17, 18}, making them ideally suited for the investigation of quantum interference at the single-molecule level caused by the Aharonov–Bohm effect. Here we report magnetoresistance measurements on individual multi-walled nanotubes, which display pronounced resistance oscillations as a function of magnetic flux.We find that the oscillations are in good agreement with theoretical predictions for the Aharonov–Bohm effect in a hollow conductor with a diameter equal to that of the outermost shell of the nanotubes. In some nanotubes we also observe shorter-period oscillations, which might result from anisotropic electron currents caused by defects in the nanotube lattice.