Electric-field-controlled spin reversal in a quantum dot with ferromagnetic contacts

Abstract

Electric-field induced control of the magnetic ground state of a carbon nanotube quantum dot enables the orientation of injected spins to be reversed without using an external magnetic field. Manipulation of the spin states of a quantum dot by purely electrical means is a highly desirable property of fundamental importance for the development of spintronic devices such as spin filters, spin transistors and single spin memories as well as for solid-state qubits1,2,3,4,5,6. An electrically gated quantum dot in the Coulomb blockade regime can be tuned to hold a single unpaired spin-1/2, which is routinely spin polarized by an applied magnetic field7. Using ferromagnetic electrodes, however, the quantum dot becomes spin polarized by the local exchange field8,9,10,11. Here, we report on the experimental realization of this tunnelling-induced spin splitting in a carbon-nanotube quantum dot coupled to ferromagnetic nickel electrodes with a strong tunnel coupling ensuring a sizeable exchange field. As charge transport in this regime is dominated by the Kondo effect, we can use this sharp many-body resonance to read off the local spin polarization from the measured bias spectroscopy. We demonstrate that the exchange field can be compensated by an external magnetic field, thus restoring a zero-bias Kondo resonance, and we demonstrate that the exchange field itself, and hence the local spin polarization, can be tuned and reversed merely by tuning the gate voltage.

Cite this article

Hauptmann, J., Paaske, J. & Lindelof, P. Electric-field-controlled spin reversal in a quantum dot with ferromagnetic contacts. Nature Phys 4, 373–376 (2008). https://doi.org/10.1038/nphys931

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