Berlin 2008 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 51: Poster IV

HL 51.33: Poster

Donnerstag, 28. Februar 2008, 16:30–19:00, Poster D

High pressure investigations of the Mott insulator GaV₄S₈ — Xin Wang¹, •Martin K. Forthaus², Karl Syassen¹, Ingo Loa¹, Dirk Johrendt³, and Mohsen M. Abd-Elmeguid² — ¹Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany — ²II Physikalisches Institut, Universität zu Köln, Köln, Germany — ³Department Chemie and Biochemie der Ludwig-Maximilians-Universität München, München, Germany

AM₄X₈ (A=Ga; M=V, Mo, Nb, Ta; X=S, Se) compounds with the cubic fcc GaMo₄S₈ type structure represent a new class of Mott insulators in which the electronic conduction originates from hopping of localized electrons (S = 1/2) among widely separated tetrahedral M₄ metal clusters. Current research on GaNb₄Se₈ and GaTa₄Se₈ show that their ground state is closely related to a structural instability: at ambient pressure they are nonmagnetic insulators, but under pressure transform to a metallic and superconducting state. In contrast, GaV₄S₈ is a ferromagnetic insulator (T_C=10 K) at ambient pressure.

For a better understanding of the electronic correlations, we have investigated the effect of pressure on the electrical transport, crystal structure, Raman modes, and infrared response of the Mott insulator GaV₄S₈. We discuss our observation of a pressure-induced insulator metal transition above 18 GPa and its possible connection to a structural instability, Raman modes and infrared response.