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Séminaire mensuel NEEL

Mardi 21 juin à 9h30,
Salle des séminaires, Bât A

Orateur : Wolfgang WERNSDORFER
"Quantum einstein de haas effect studied with molecular spintronic devices"


One hundred years ago it has been discovered that a change of magnetization in a macroscopic magnetic object results in a mechanical rotation of this magnet.1 The effect, known as Einstein de Haas or Richardson effect, demonstrates that a spin angular momentum in the magnet compensates for the mechanical angular momentum associated with its rotation. The experiment is therefore a macroscopic manifestation of the conservation of total angular momentum and energy in eletronic spins. According to Noether’s theorem, conservation of angular momentum follows from a system`s rotational invariance and would be valid for the ensemble of spins in a macroscopic ferromagnet as well as for an individual spin. It has been recently proposed that single spin systems would therefore manifest an Einstein de Haas effect at the quantum level.2
Here we propose the first experimental realization of a quantum Einstein-de Haas experiment and describe a macroscopic manifestation of the conservation of total angular momentum in individual spins, using a single molecule magnet coupled to a nanomechanical resonator. We demonstrate that the spin associated with the single molecule magnet is then subject to conservation of total angular momentum and energy which results in a total suppression of the molecule’s quantum tunneling of magnetization.3

Figure : For the quantum Einstein-de Haas experiment, the false color scanning electron micrograph shows a suspended carbon nanotube with a local metallic backgate (red) functionalized with a TbPc2 single molecule magnet. Due to conservation of the total angular momentum, the magnetization reversal of J = 6 (white arrow) in a magnetic field results in a rotation of the single molecule magnet (blue arrow), thus generating a quantized phonon mode in the carbon nanotube nanoelectromechanical resonator.

1. A. Einstein and W.J. de Haas, Deutsche Physikalische Gesellschaft, Verhandlungen, 1915, 17, 152.
2. E. M. Chudnovsky and D. A. Garanin, Phys. Rev. Lett., 1994, 72, 3433 ; Phys. Rev. B, 2010, 81, 214423 ; Phys. Rev. B, 2005 72, 094426 ;
 Phys. Rev. X, 2011, 1, 011005.
3. M. Ganzhorn, S. Klyatskaya, M. Ruben, W. Wernsdorfer, Nature Nanotechnol., 2013, 8, 165 ; Nature Comm., 2016.

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