Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 88: Transport: Carbon Nanotubes

TT 88.3: Talk

Thursday, March 19, 2015, 10:00–10:15, A 053

Thermally induced subgap features in the cotunneling spectroscopy of a carbon nanotube — Sascha Ratz¹, •Andrea Donarini¹, Daniel Steininger², Thomas Geiger², Amit Kumar², Andreas Huettel², Christoph Strunk², and Milena Grifoni¹ — ¹Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany — ²Institute for Experimental and Applied Physics, University of Regensburg, 93040 Regensburg, Germany

We report on the nonlinear cotunneling spectroscopy of a carbon nanotube quantum dot coupled to Nb superconducting contacts [1]. Our measurements show rich subgap features in the stability diagram which become more pronounced as the temperature is increased.
Subgap features in the tunnelling spectroscopy of hybrid superconductor-quantum dot structures are commonly attributed to Andreev reflection processes. However, applying a transport theory based on the Liouville-von Neumann equation for the density matrix, we show that, in the parameter range of our experiments, the subgap transport properties can be attributed solely to processes involving sequential as well as elastic and inelastic cotunneling of quasiparticles thermally excited across the gap. In particular, we predict thermal replicas of the elastic and inelastic cotunneling peaks, in agreement with our experimental results.

[1] S. Ratz, A. Donarini, D. Steininger et al. accepted by NJP, arXiv:1408.5000v2.