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20.01.2016

13.05.2016: Publication in Nature by B4 (Koch/Kira)

Collision experiments in semiconductors come into reach - The standard model and understanding of matter and interactions rests upon evidence gathered from particle accelerators and collider experiments. Material science strives at controlling the complex interactions among the billions upon billions of particles within a solid. Fortunately, this challenge boils down to knowing the physics of simple entities created by interactions, so-called quasiparticles that actually drive the elementary processes such as charge transport and light emission/absorption. Although, e.g., nanotechnology crucially depends on knowing the quasiparticle-driven processes, a collider concept has not been demonstrated for them. A team of physicists from Marburg, Regensburg, and Santa Barbara (USA) have now realized a collider for quasiparticles in solids.


collision-image
An electron (blue) and a hole (red) collide in a tungsten diselinide crystal releasing energy which discharges in high-energy photons (colored lightbeam). Illustration: Fabian Langer (image-use solely granted for reporting related to the scientific publication).

This theory-experiment collaboration studied quasiparticles within WSe2, a layered material whose van-der Waals interfaces are topic of increasing importance also for the SFB 1083. Since the quasiparticles only exist for a flash of time, it was crucial to operate on ultrashort timescales. This team used a unique laser source (terahertz high-field lab, Regensburg) to produce hard evidence on collisions within excitons, which are pairs of electrons and holes (electron vacancies) bound by the attractive Coulomb-force between them, in a thin crystal of WSe2. In their scheme, a femtosecond optical pulse creates coherent excitons at a precise time with respect to an intense light pulse in the terahertz (THz) spectral regime. The lightwave of the THz pulse then accelerates the constituents of the exciton, i.e. electrons and holes, within a period shorter than a single oscillation of light. The experiment shows that only excitons created at the right time lead to electron–hole collisions, just as in conventional synchrotron accelerators. This re-collision generates electron–hole annihilation yielding ultrashort light bursts encoding key aspects of the solid. Like in “ordinary” colliders, a full quantum theory (Marburg) was applied to assign the quasiparticle properties and their interactions to collision outcomes, here the emerging new frequency components in the light emission, making this demonstration complete. The proposed quasiparticle-collider concept is directly applicable to study a broad range of systems and quasiparticles, such as biexcitons, dropletons, polarons, Cooper pairs, and so on. All one needs is an electric charge that the lightwave can couple to. This work is partially supported by DFG through SFB 1083 and SPP 1840.

( Deutsche Pressemitteilung)

Publication:

F. Langer, M. Hohenleutner, C. Schmid, C. Poellmann, P. Nagler, T. Korn, C. Schüller, M. S. Sherwin, U. Huttner, J. T. Steiner, S. W. Koch, M. Kira, and R. Huber
Lightwave-driven quasiparticle collisions on a sub-cycle timescale
Nature 533 (2016) 225-229 DOI:10.1021/acs.jpclett.6b00299

Kontakt

Prof. Dr. Mackillo Kira
Philipps-Universität Marburg
SFB 1083 subproject B4
http://www.uni-marburg.de/sfb1083/projects/B4

Tel.: +49 (0)6421 28-24222
E-Mail

Zuletzt aktualisiert: 09.02.2021 · pfuhlh

 
 
 
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