Dresden 2009 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 9: Correlated Electrons: Metal-Insulator Transition 1

TT 9.6: Vortrag

Montag, 23. März 2009, 15:30–15:45, HSZ 03

Electronic and optical properties of NiS₂ — •Cosima Schuster — Universität Augsburg, D-86135 Augsburg

Crystal field splitting, correlation, and the 3d band width are almost equal in the pyrites MX₂ (M=Fe,Co,Ni; X=S,Se) which gives rise to a large variety of electrical, magnetic and optical properties in these compounds. Of special interest is the metal-insulator-transition in NiS₂ with Se-doping or by applied pressure. It is not accompanied by a change in the lattice symmetry and commonly believed to be driven by electron-electron interactions. In addition, a low-temperature antiferromagnetic phase is observed both in the insulating and metallic regime. To reinvestigate the properties of NiS₂ we perform ab initio calculations using density functional theory. Thereby we focus on the relation between doping and applied pressure and the role of the magnetism in the metal-insulator-transition. The magnetic phase diagram with pressure and doping can be reproduced within the GGA, albeit the magnetic phase is slightly overestimated. The insulating behaviour of NiS₂, however, cannot be described within this approximation. The description in terms of a gap and of the metal-insulator-transition and the optical properties near the transition need more advanced methods. The response functions obtained in the random phase approximation cannot sufficiently describe the optical properties.