Regensburg 2013 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 16: Transport: Quantum Dots, Wires, Point Contacts 2 (jointly with HL)

TT 16.1: Talk

Monday, March 11, 2013, 15:00–15:15, H18

Bound States in a Carbon Nanotube Quantum Dot Coupled to Superconducting Leads — •Amit Kumar¹, Martin Gaim¹, Daniel Steininger¹, Andreas K. Hüttel¹, Christoph Strunk¹, Alfredo Levy Yeyati², and Alvaro Martín-Rodero² — ¹Institute for Experimental and Applied Physics, University of Regensburg, 93040 Regensburg, Germany — ²Department of Theoretical Condensed Matter Physics, Universidad Autónoma de Madrid, 28049 Madrid, Spain

We report on tunnelling spectroscopy measurements on a carbon nanotube quantum dot device strongly coupled with niobium superconducting leads at two ends and weakly coupled to a tunnel probe (aluminium) in the middle. Gate dependent differential conductance measurements at low temperature down to 25mK reveal the formation of bound states (Andreev / Yu-Shiba Rusinov) inside the superconducting gap. By virtue of the larger superconducting gap of the niobium, we observe several such states. Odd Coulomb valleys show negative differential conductance features, which are characteristics for bound states with localized spins. These localized spins (odd number of electrons on the quantum dot) are known to generate localized Yu-Shiba Rusinov bound states inside the superconducting gap and are expected to dominate in asymmetrically coupled quantum dot devices. More detailed experimental investigations and theoretical calculations are in progress to understand these experimental findings.