Inelastic tunneling spectroscopy for magnetic atoms and the Kondo resonance.

E. C. GOLDBERG; F. FLORES

Paris

Congreso; IVC-19/ICN+T 2013; 2013

Inelastic tunneling spectroscopy of single magnetic atoms [1-3] and single molecule magnets [4-5] has been recently used to explore the strength, and its anisotropies, of their intrinsic spin. In the single magnetic atom case, Fe or Co have been deposited on a CuN surface, so that the electrons injected with a STM-tip across a single atom interact with the magnetic spin creating spin-flip processes that reveal themselves in the tip-metal tunneling conductance measured as a function of the bias voltage. In this work we address that problem by introducing an ionic Hamiltonian [6] for describing the d-electrons of the magnetic atom, and analyze the tunneling current for a metal/atom/tip configuration using a Green-function Equation of Motion method [7-8].  We analyze in the case of Fe on CuN the possible spin fluctuations between states with S=2 and S=3/2 or 5/2 and conclude, from the found asymmetries and marked structures in the conductance, that the S=2 to S=3/2 fluctuations are dominant and provide a good description of the experimental data. The case of Co is also considered and shown to present, in contrast with Fe, a resonance at the Fermi energy corresponding to a Kondo temperature of 6K. The strong dependence of the spin excitations on magnetic field direction observed experimentally is also well reproduced by our calculations.     1 C. F. Hirjibehedin et al., Science 317, 1199 (2007). 2 A.F. Otte et al, Nature Physics 4, 847 (2008) 3A.F. Otte et al, Phys Rev Lett 103, 107203 (2009) 4J. J. Parks et al., Science 328, 1370 (2010) 5 A. S. Zyazin et al., Nano Lett. 10, 3307 (2010). 6A. C. Hewson, The Kondo Problem to Heavy Fermions, (Cambridge University press, Cambridge, 1993). 7 E. C. Goldberg and F. Flores, Phys. Rev. B 77, 125121 (2008).