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Soutenance de Thèse

Marc GANZHORN (Institut Néel)

Directeur de thèse : Wolfgang WERNSDORFER

The magnetism of a nanoscale object, like single molecule magnets or atoms, is typically governed by the laws of quantum mechanics. Various quantum effects ranging from tunneling processes to coherent phenomena have for instance been observed in single molecule magnets [1]. Probing the quantum nature of such molecular magnets however remains a challenging task and requires the use of an appropriate magnetometer, preferably one with molecular dimensions itself [1]. Following the trend of carbon nanotube based magnetometers, we will present a promising magnetometer design based on a carbon nanotube nano electromechanical system (NEMS). In order to achieve a molecular sensitivity, the carbon nanotube NEMS should exhibit large quality factors and allow a strong coupling to a molecular magnet [2]. We will show an ultraclean, bottom up fabrication process, enabling the assembling of carbon nanotube NEMS with quality factors as high as 105. Moreover we will demonstrate that the quality factors can be tuned over 3 orders of magnitude by modifying the carbon nanotube’s electrostatic environment [3]. In a second part, we will demonstrate a strong coupling of a carbon nanotube’s quantized mechanical motion to the magnetization of a terbium double decker single molecule magnet. As a consequence of the strong spin-phonon coupling, we can observe the nuclear spin states of the terbium ion in the molecule in magnetization reversal measurements at cryogenic temperatures [4]. With both conditions satisfied, a carbon nanotube NEMS therefore makes an ideal candidate for a single molecule magnetometer.

[1] L. Bogani, W. Wernsdorfer, Molecular spintronics using single-molecule magnets, Nature Mat. 7, 179 (2008). [2] Lassagne, B., Ugnati, D. & Respaud, M. Ultrasensitive magnetometers based on carbon nanotube mechanical resonators. Phys. Rev. Lett. 107, 130801 (2011). [3] M. Ganzhorn and W. Wernsdorfer, Dynamics and dissipation induced by SET in carbon nanotube NEMS. Phys. Rev. Letts 108, 175502 (2012). [4] M. Ganzhorn, S. Klyatskaya, M. Ruben, W. Wernsdorfer, Strong spin-phonon coupling between a single-molecule magnet and a carbon nanotube nanoelectromechanical system, Nature Nanotechnology (2013) doi:10.1038/nnano.2012.258

ATTENTION : Cette soutenance aura lieu en anglais.

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