Observation and spectroscopy of a two-electron Wigner molecule in an ultraclean carbon nanotube

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Two electrons on a string form a simple model system where Coulomb interactions are expected to play an interesting role. In the presence of strong interactions, these electrons are predicted to form a Wigner molecule, separating to the ends of the string. This spatial structure is believed to be clearly imprinted on the energy spectrum, yet so far a direct measurement of such a spectrum in a controllable one-dimensional setting is still missing. Here we use an ultraclean carbon nanotube to realize this system in a tunable potential. Using tunnelling spectroscopy we measure the addition spectra of two interacting carriers, electrons or holes, and identify seven low-energy states characterized by their exchange symmetries. The formation of a Wigner molecule is evident from a tenfold quenching of the fundamental excitation energy as compared with the non-interacting value. Our ability to tune the two-carrier state in space and to study it for both electrons and holes provides an unambiguous demonstration of this strongly interacting quantum ground state.
Original languageEnglish
JournalNature Physics
Volume9
Pages (from-to)576-581
Number of pages6
ISSN1745-2473
DOIs
Publication statusPublished - 28 Jul 2013

Bibliographical note

Preprint available at http://arxiv.org/abs/1302.1877.

ID: 91302444