Regensburg 2022 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 2: Nanotubes, Nanoribbons and Graphene

TT 2.1: Talk

Monday, September 5, 2022, 09:30–09:45, H22

Magnetic field control of the Franck-Condon coupling of few-electron quantum states — Peter L. Stiller, Daniel R. Schmid, Alois Dirnaichner, and •Andreas K. Hüttel — Institute for Experimental and Applied Physics, Universität Regensburg, Regensburg, Germany

The longitudinal vibration of a suspended carbon nanotube has been observed many times in low temperature transport spectra via distinct harmonic Franck-Condon sidebands. Typically, strong Franck-Condon coupling has been attributed to disorder-induced or deliberately targetted charge localization. Here, we present the observation of a strong, tunable coupling in an ultra-clean carbon nanotube with N=1 or N=2 electrons in the conduction band. The clean transport spectrum allows a tentative identification of the electronic base quantum states according to their valley quantum number. Interestingly, the Franck-Condon coupling strength g, as extracted from our data, both depends on the magnetic field and on the precise electronic quantum states participating in transport. While spin-dependent Franck-Condon phenomena have already been observed, our results clearly point towards a valley-dependent origin. As possible cause of this phenomenon, re-shaping of the electronic wavefunction envelope by the magnetic field is discussed. A simple calculation demonstrates that variations of g as observed in the experiment can be reproduced by the theory, paving the way towards more realistic and detailed quantum-mechanical modelling.