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Originally published in Science Express on 30 April 2009
Science 22 May 2009:
Vol. 324. no. 5930, pp. 1044 - 1047
DOI: 10.1126/science.1171472
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Reports

Dispersion of the Excitations of Fractional Quantum Hall States

Igor V. Kukushkin,1,2 Jurgen H. Smet,1,* Vito W. Scarola,3,4 Vladimir Umansky,5 Klaus von Klitzing1

The rich correlation physics in two-dimensional (2D) electron systems is governed by the dispersion of its excitations. In the fractional quantum Hall regime, excitations involve fractionally charged quasi particles, which exhibit dispersion minima at large momenta referred to as rotons. These rotons are difficult to access with conventional techniques because of the lack of penetration depth or sample volume. Our method overcomes the limitations of conventional methods and traces the dispersion of excitations across momentum space for buried systems involving small material volume. We used surface acoustic waves, launched across the 2D system, to allow incident radiation to trigger these excitations at large momenta. Optics probed their resonant absorption. Our technique unveils the full dispersion of such excitations of several prominent correlated ground states of the 2D electron system, which has so far been inaccessible for experimentation.

1 Max Planck Institute for Solid State Research, D-70569 Stuttgart, Germany.
2 Institute of Solid State Physics, Russian Academy of Science, Chernogolovka 142432, Russia.
3 Department of Chemistry and Pitzer Center for Theoretical Chemistry, University of California at Berkeley, Berkeley, CA 94720, USA.
4 Theoretische Physik, Eidgenössische Technische Hochschule Zürich, 8093 Zürich, Switzerland.
5 Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel.

* To whom correspondence should be addressed. E-mail: j.smet{at}fkf.mpg.de

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
A Sound (and Light) Way to Measure Confined Electrons.
S. H. Simon (2009)
Science 324, 1022-1023
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