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Orbitally phase coherent spintronics
Spin valves implement to some extent the analog of a polarizer/analyzer experiment in optics. This analogy is at the heart of the principle of the celebrated proposal by Datta and Das for a spin field effect transistor and can be transposed to any type of spintronics device. One of the goals of our research is to study how such an analogy can be used to find means to control the electronic spin. The optical analogies are also particularly illuminating for understanding transport in mesoscopic conductors in which the phase of the electronic function is well defined. Essentially thanks to their low number of conducting channels, single wall carbon nanotubes offer the possibility to study the interplay between spin dependent transport in the traditional sense (i.e. with ferromagnetic contacts) and orbitally phase coherent transport. This property can be indirectly exploited in two-terminal devices but is particularly striking in multi-terminal (more than two) devices.
In order to study these phenomena, we fabricate (see Chéryl Feuillet-Palma thesis) structures of the type of the one in the main page (center), using two inner NiPd contacts and two outer Pd contacts separated by 500 nm roughly. For temperatures below 10K, these devices behave as triple quantum dots connected to four reservoirs-two normal and two ferromagnetic. In order to control the electronic transport via the local electric field, we have implemented lateral gates to tune independently the two outer dots. In cases where we can neglect electron-electron interactions, this type of device can be viewed as a series of electronic Fabry-Perot interferometers.
Références : C. Feuillet-Palma et al. Phys. Rev. B 81, 115414 (2010) A. Cottet, C. Feuillet-Palma and T. Kontos Phys. Rev. B 79, 125422 (2009)