Workshop book - Physikzentrum der RWTH Aachen - RWTH Aachen ...

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Posters Monday February 4 Poster 3: Influence of magnetic anisotropy on the un<strong>der</strong>screened Kondo effect in the presence of ferromagnetism Maciej Misiorny The prominent role of magnetic anisotropy (MA) in formation of the Kondo effect has recently been demonstrated experimentally [1,2]. In particular, it turned out that in systems of spin S>1/2, such as magnetic adatoms (i.e. Fe, Co or Mn) or magnetic molecules, the Kondo effect can be tuned by modifying the system’s MA. Furthermore, theoretical studies also indicate that MA can be a key factor determining spin-polarized transport through a magnetic nanosystem [3]. Motivated by the recent experiment [2], in this communication we address how the MA affects the un<strong>der</strong>screened Kondo effect (i.e. partial compensation of the molecular spin by conduction electrons) in the case of an artificial molecule of spin S=1 coupled to a reservoir of spin-polarized conduction electrons [4]. The crucial ingredient of the model is the presence of uniaxial MA. The problem is analyzed by means of Wilson’s numerical renormalization group (NRG) method, which allows for calculating the spectral function of the molecule. We show that the interplay of MA and ferromagnetism has a fundamental significance for occurring of the Kondo effect. Most importantly, despite the presence of the effective exchange field [5] the Kondo effect can be restored by adjusting the magnitude of MA. 1. A.F. Otte et al., Nature Phys. 4, 847 (2008). 2. J.J. Parks et al., Science 328, 1370 (2010). 3. M. Misiorny, I. Weymann and J. Barnas, Phys. Rev. Lett. 106, 126602 (2011); Phys. Rev. B 84, 035445 (2011). 4. I. Weymann and L. Borda, Phys. Rev. B 81, 115445 (2010). 5. J. Martinek et al., Phys. Rev. Lett. 91, 127203 (2003); Phys. Rev. B 72, 121302 (2005). Coauthors I. Weymann and J. Barnaś 60
Posters Monday February 4 Poster 4: Kondo effect and magnetic frustration in a system of magnetic trimer on a metal surface Hoa Nghiem We use quantum Monte Carlo simulation to clarify the competition between Kondo screening and magnetic frustration in a system of three magnetic adatoms on a metal surface [1]. We observe the feature of spectral density depending on the geometric configuration of three magnetic adatoms on the surface [2, 3]. In the isosceles configuration, the spectral density exhibits a significant peak near the Fermi level, which we attribute to the Yosida-Kondo resonance. In the equilateral configuration, no peak is observed near the Fermi level. This observation suggests the two separate regimes; the Yosida- Kondo dominant regime with the singlet ground state, and the magnetic frustration dominant regime with the degenerate ground state, - changing from one regime to another is realized as we gradually switch the geometric configuration from the isosceles triangle to equilateral one. By calculating the spectral density and the magnetic susceptibility in a wide range of temperatures, we prove the existence of the two separate regimes and suggest the critical crossover between them. [1] N. T. M. Hoa, W. A. Dino, and H. Kasai: J. Phys. Soc. Jpn. 81 (2012) 023706. [2] T. Jamneala, V. Madhavan, and M. F. Crommie: Phys. Rev. Lett 87 (2001) 256804. [3] N. T. M. Hoa, W. A. Dino, and H. Kasai: J. Phys. Soc. Jpn. 79 (2010) 113706. Poster 5: Spin dynamics in nanoparticles near Stoner instability Philipp Stegmann We analyse the spin dynamics of a nanoparticle close to the Stoner instability. The nanoparticle is weakly tunnel coupled to two ferromagnetic leads. By mapping to an effective Fokker-Planck description we identify two different types of dynamic behaviour (diffusion vs. drift), which are revealed by characteristic relaxation times and a Fano factor that oscillates as a function of an applied bias voltage. Finally, we propose biasing schemes to generate states with magnetic quadrupole moments that dominate over a negligible dipole moment. 61
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PROGRAM BOOK International workshop
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What comes with this booklet With t
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Getting to the institute (1) If you
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Workshop lecture hall • The works
Page 9 and 10: Lunch information Lunch will be tak
Page 11 and 12: Talks Monday February 4 Talk progra
Page 13 and 14: Talks Monday February 4 Notes 13
Page 29 and 30: Talks Tuesday February 5 Talks Tues
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Page 47 and 48: Talks Wednesday February 6 Talks We
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Page 72 and 73: Posters Tuesday February 5 Poster 2
Page 86 and 87: 18. Domenico Giuliano, Universita
Page 88 and 89: 55. Jens Paaske, Copenhagen Univers
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