(Poster) Spin-dependent coupling to vibrations in suspended carbon nanotube quantum dots

HERNAN L. CALVO; JULIAN BOHLE; CHRISTOPH STAMPFER; MAARTEN R. WEGEWIJS

Obergurgl

Workshop; Frontiers in Quantum Engineered Devices; 2013

<!-- @page { margin: 0.79in } P { margin-bottom: 0.08in } -->Recent transport experiments in a semi-suspended carbon nanotube (CNT) quantum dot have shown an electron-vibration coupling that is markedly different for spin singlet and triplet states. In this contribution, we show that such an apparent spin-vibration coupling can be understood in terms of a coupling of the electronic valley degree of freedom of the CNT to the observed longitudinal vibration. Strikingly, this Peierls type coupling in the valley space leads to Franck-Condon sidebands that mostly develop for the triplet excited state. A vibrational modulation of the exchange interaction on the CNT is shown to result in a similar, but weaker effect. The effect can be understood qualitatively from polaronic shifts obtained in the Born-Oppenheimer approximation. In the regimes of interest, however, this approximation breaks down and we present transport calculations accounting for the full pseudo-Jahn-Teller mixing of the vibronic states that show satisfactory agreement with the experiment.