Structural investigation of the insulator-metal transition in NiS2−xSex compounds*

We report [1] on a combined measurement of high-resolution x-ray diffraction on powder and Raman scattering on single crystalline NiS2-xSex samples that exhibit the insulator-metal (IM) transition [2] with Se doping. Via x-rays, an abrupt change in the bond length between Ni and S (Se) ions was observed at the transition temperature, in sharp contrast to the almost constant bond length between chalcogen ions. Raman scattering, a complementary technique with the unique sensitivity to the vibrations of chalcogen bonds, revealed no anomalies in the phonon spectrum, consistent with the x-ray diffraction results. This indicates the important role of the interaction between Ni and S (Se) in the IM transition. The potential implication of this interpretation is discussed in terms of current theoretical models.

[1] Garam Han, Sungkyun Choi, Hwanbeom Cho, Byungmin Sohn, Je-Geun Park, and Changyoung Kim, Physical Review B 98, 125114 (2018).
[2] For a review, see M. Imada, A. Fujimori, and Y. Tokura, Rev. Mod. Phys. 70, 1039 (1998) and references therein.