"Many-body interaction induced exotic phenomena at surface: molecular Kondo effect and inelastic process in laser-photoemission"

Who: Emi Minamitani (Department of Materials Engineering, The University of Tokyo)

Place: Donostia International Physics Center (DIPC)

Date: Friday, 11 September 2015, 12:00

Many-body interaction induced exotic phenomena at surface: molecular Kondo effect and inelastic process in laser-photoemission

 

Emi Minamitani

Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku Tokyo, Japan

 

Recent development of the theoretical/experimental techniques enables us to explore low-energy excitations induced by many-body interaction at surface. In this talk, I will introduce two of my theoretical studies in this field: 1) Kondo effect in molecules at surfaces, 2) inelastic process appears in laser-photoemission spectroscopy.

 

The Kondo effect [1] is one of the intriguing phenomena arising from the interaction between localized magnetic moments and conduction electrons. The Kondo singlet state resulting from the Kondo effect changes the magnetic state and the conductivity drastically, which yields a sharp peak or dip structure at the Fermi level in scanning tunneling spectrum (STS). Recently, the observations of the Kondo effect by STS have been reported in various phthalocyanine and porphyrin molecules on metal surfaces [2]. To elucidate the mechanism of molecular Kondo effects, I have carried out theoretical studies by density functional theory (DFT) and numerical renormalization group (NRG) in collaboration with experimental groups. In this talk, I will introduce the results on Mn-phthalocyanine (MnPc) on Pb(111), in which the ?-d interaction plays a crucial role to mediate indirect Kondo screening and form a spatially extended Kondo state [3].

 

Laser-photoemission spectroscopy (LPES) at metal surface with low-energy photons of ~ 5eV can probe phonons at surfaces through the photoelectron-phonon interaction. The inelastic interaction produces a spectral component whose shape is a replica of the elastic one downshifted by the vibrational energy relative to the Fermi level. Such inelastic LPES signals have been observed in CO/Cu(001) [4] and clean Cu(110) surface [5], but the mechanism of the phonon excitation during the photoemission process remained unanswered. I investigated this inelastic excitation process on Cu(110) using ab-initio calculations including electron-phonon coupling calculation based on the density functional perturbation theory. As a result, I found strong wavevector and energy dependence in the electron-phonon coupling, which causes selective excitation of the subsurface phonon by photoelectron [6].

 

I thank Prof. N. Takagi, Prof. M. Kawai, Dr. N. Tsukahara, Dr. R. Arafune, Dr. Y. Kim, Dr. Y. Fu, Prof. Q. K. Xue, and Prof. S. Watanabe for discussions and collaboration in the works presented in

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