Spin-polarized electron transport through selected molecules by means of spin-polarized scanning tunneling microscopy
Final Report Abstract
In the last decades, remarkable progress has been made in semiconductor industry towards the miniaturization of electronic devices. The physical limits of this top-down approach, however, will be reached in the foreseeable future and devices of the size of single molecules will be required. Thus, the understanding of the transport properties on the molecular scale plays an important role. A second and very successful approach to increase the functionality of electronic circuits is to not only use the electron charge but also its spin. The field of spintronics started with the discovery of the giant magnetoresistance (GMR) in 1988 has already lead to broad applications. This project focused on merging the concepts of molecular electronics with that of spintronics to introduce molecular spintronics, i.e. combined spin and charge transport across single molecules. In this project, single Phthalocyanine molecules were contacted to determine their conductance. Due to the fact, that the molecules jump into contact to the tip of the scanning tunneling microscope when the latter is approached close enough, the molecular conductances could be determined very precisely. This allowed in a second step to determine the dependence of the molecular conductance on the magnetization configuration of the two contacting magnetic electrodes (tip and sample surface). These measurements revealed a large GMR of about 60% in combination with low resistances of the order of 100 kΩ. This combination is ideal of technical applications in read heads, as not only a large magnetic signal is present but also the resistance is low enough to allow high frequency operation. This finding can be considered as a major break through in molecular spintronics and has attracted significant attention of the community of spintronics and molecular electronics. Finally, Cr(acac)3 molecules were evaporated onto non magnetic Cu(111) surfaces and a strong zero bias anomaly was found that is in agreement with a Kondo resonance of the Cr spin 1/2 system. It was fund that this Kondo resonance effectively couples to the twodimensional electron gas of the Cu(111) surface state.
Publications
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Electron transport through single phthalocyanine molecules with STM. Physical Review B 78, 233404 1-4 (2008)
A.F. Takacs, F. Witt, S. Schmaus, T. Balashov, M. Bowen, E. Beaurepaire, W. Wulfhekel
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Impact on Interface Spin Polarization of Molecular Bonding to Metallic Surfaces. Physical Review Letters 105, 077201 1-4 (2010)
S. Javaid, M. Bowen, S. Boukari, L. Joly, J.-B. Beaufrand, Xi Chen, Y. J. Dappe, F. Scheurer, J.-P. Kappler, J. Arabski, W. Wulfhekel, M. Alouani, E. Beaurepaire
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Giant magnetoresistance through a single molecule. Nature Nanotechnology 6, 185-189 (2011)
S. Schmaus, A. Bagrets, Y. Nahas, T.K. Yamada, A. Bork, M. Bowen, E. Beaurepaire, F. Evers, W. Wulfhekel
