## Local Structure and Electron-lattice Coupling | Shull Wollan Center

ABSTRACT:

Today it may appear that electronic structure is well understood theoretically in metals and semiconductors, even in strongly correlated electron systems [1]. Their electronic structure has been observed experimentally by modern state-of-the-art photoemission spectroscopies, such as angle resolved photoemission spectroscopy. The results often show that there are some deviations from the calculated band structure with the mean field approximation. In the strongly correlated electron materials, their electronic band structure can be described by electronic structure of their local clusters possibly due to the localized electron characters [2], where quantum numbers, such as orbital momenta, can be good measure at every atom. The local cluster model helps us to understand the physical properties such as electron-phonon interaction based on the bond order. The magnetic excitation spectrum is also a good measure for the electron correlation of materials. For this purpose, inelastic neuron scattering is one of the most powerful tools to reveal the effect. For example, LaFePO system is regarded as a weak electron correlation limit in the Fe-based superconductors due to the wide band width [3]. The magnetic excitation spectrum of LaFePO0.9 measured by inelastic neutron scattering suggests the importance of electron correlation [4], but there are still large differences between the observed and calculated inelastic neutron scattering spectra [1,4]. In addition, the Mott quantum critical points generally exhibit phase separations as a first order phase transition [5]. It may be intriguing to revisit their structure as a function of electronic parameters such as band width and carrier numbers, which must have a strong correlation with electron-lattice coupling. Recent crystallographic developments with high-intensity quantum beams show local lattice distortions in crystalline materials which are hidden in the standard crystallographic analysis [6].  Here, some of structural studies will be introduced as examples of strong interplay between local structures and their physical properties [7].

References

[1] Z. P. Yin, K. Haule and G. Kotliar, Nature Phys. 10, 845 (2014).

[2] A. Fujimori et al., Solid State Commun. 63, 857 (1987).

[3] V. Vildosola et al., Phys. Rev. B78, 064518 (2008).

[4] M. Ishikado, S. Shamoto et al., submitted to Sci. Rep..

[5] B. A. Frandsen et al, Nature Commun.  7, 12519 (2016).

[6] T. Egami and S. J. L. Billinge, “Underneath the Bragg Peaks Structural Analysis of Complex Materials”, Pergamon (2003).

[7] S. Shamoto, to be submitted to a special issue of J. Phys. Soc. Jpn.

## Date:

Tuesday, September 11, 2018 - 16:00 to 17:00

## Speaker Name:

Shin-ichi Shamoto, Advanced Science Research Center, Japan Atomic Energy Agency

## Location:

Shull Wollan Center (ORNL Bldg. 8630), Room A202

Takeshi Egami