Dispersion of the Excitations of Fractional Quantum Hall States

• Published in: Science (American Association for the Advancement of Science) Vol. 324; no. 5930; pp. 1044 - 1047
• Main Authors: Kukushkin, Igor V, Smet, Jurgen H, Scarola, Vito W, Umansky, Vladimir, von Klitzing, Klaus
• Format: Journal Article
• Language: English
• Published: United States American Association for the Advancement of Science 22.05.2009; The American Association for the Advancement of Science
• Subjects: absorption; Dispersion; Electrons; Fermions; Magnetic fields; Mathematical minima; Microwaves; Momentum; Optical resonance; Optics; Particle physics; Quantum physics; Rotons; sounds; Surface acoustic waves; Transducers; Wave excitation
• ISSN: 0036-8075; 1095-9203; 1095-9203
• DOI: 10.1126/science.1171472

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.