Prof. Erio Tosatti: Atomic and Molecular Nanocontacts: Structure, Magnetism, and Kondo Anomalies from First Principles
Source: Monday physics colloquium
Atomic and Molecular Nanocontacts: Structure, Magnetism, and Kondo Anomalies from First Principles
Prof. Erio Tosatti, SISSA, ICTP, and CNR-IOM Democritos, Trieste
The nature and properties of atomic and molecular metallic nanocontacts, of break junctions, and of tip based tunnel junctions are difficult to access geometrically, yet very rich of phenomena in connection with structure, electron transport, and magnetism. Structurally, the formation of magic nanowires in gold  is a remarkable phenomenon, explained by minima of the string tension. Electronically, first principles calculations can account well for the ballistic conductance of metal nanocontacts, both in nonmagnetic and in magnetic metals. [3,4] Magnetic impurities bridging nonmagnetic metal contacts yield zero bias anomalies in STS spectra and/or in ballistic conductance due to the Kondo effect. Qualitatively similar to those of quantum dots, these anomalies are dominated in this case by the specificities of the atomic and molecular states involved, only accessible through a first principles electronic structure approach. The difficulty to combine the Kondo many body physics with the mean-field ielectronic structure poses a problem. We address this problem by means of a joint density functional plus numerical renormalization group approach recently devised. I will illustrate applications to transition metal impurities on gold nanowires and on carbon nanotubes, and to magnetic molecules on gold surfaces. The circumstances conducive to ferromagnetic Kondo effect, as opposed to ordinary antiferromagnetic Kondo, will also be outlined along with possible systems where that unusual situation could be realized.[5,7]
(*) Recent work in collaboration with P.P. Baruselli, M. Fabrizio, R. Requist, A. Smogunov.
 Y. Kondo, K. Takayanagi, Science 289, 606 (2000).
 E. Tosatti et al., Science, 291, 288 (2001).
 A. Smogunov et al., Phys.Rev. B 70, 045417 (2004).
 A. Smogunov et al, Phys. Rev. B 74, 045429 (2006).
 P. Lucignano, et al., Nature Materials 8, 563 (2009).
 P. P. Baruselli et al., Phys. Rev. Lett. 108, 206807 (2012).
 P. Gentile, et al. EPL, 87 27014 (2009).