ELFT HÍRADÓ

[tcsaba AT eik.bme.hu]

                                MEGHÍVÓ

          a BME Fizikai Intézete Elméleti Fizika Tanszékének

                            szemináriumára:


                             Keisuke Hatada
            Groupe Théorie, Département Matériaux-Nanosciences,
                 Institut de Physique de Rennes, UMR
            UR1-CNRS 6251, Université de Rennes1, France


             "Full Potential Multiple Scattering theory for
           space-filling cell in real space and its application
         to Core electron excitation spectra and investigation of
      saturable absorption by ultra short Free Electron Laser pulse"


Multiple Scattering theory which is known as KKR for band calculation  
is widely
used in calculation of various spectroscopies to compute the continuum state.
Conventionally Multiple Scattering approach relies on Muffin-Tin (MT)
approximation, where the potential is spherically symmetrized and confined
within non-overlapping spheres, while it takes a constant value in the  
interstitial
region. This approximation fails for low dimensional systems and diamond type
structures. We have developed the Full Potential Multiple Scattering (FPMS)
theory beyond the approximation and implemented its code FPMS.1) Our method
avoids the expansion of the shaped potential by spherical harmonics which
creates bad convergence. We applied the method to anisotropic systems, open
molecules and grapheme-related systems.

Saturable absorption using ultra short X-ray pulses was recently observed at
FLASH free-electron-laser (FEL) facility in transmission measurements of pure
Al thin films above the LII,III edge.2) We devised a theoretical model  
describing
this phenomenon (See Fig. 1).3) This phenomenological model explicitly
involves the interaction between solid and photon field in semi-classical way,
and the resulting non-linear coupled equation is solved numerically. We
successfully applied this model to our recent experimental results obtained by
using FEL radiation in Elettra AT FERMI.3,4)

[References]
1) K. Hatada, K. Hayakawa, M. Benfatto and C. R. Natoli, Phys. Rev. B  
76, 060102(R) (2007).
2) B. Nagler et al., Nature Physics 5, 693 (2009).
3) K. Hatada and A. Di Cicco, J. Elect. Spec. Relat. Phenom., 196, 177 (2014).
4) A. Di Cicco, K. Hatada et al.
, Phys. Rev. B 90, 220303(R)  
(2014)
.


Helye: BME Fizikai Intézet, Elméleti Fizika Tanszék
Budafoki út 8. F-épület, III lépcsöház
Szemináriumi szoba

Ideje: 2015. április 22. péntek, 10:15.


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