The Application of the Mössbauer Effect for Probing Electronic Properties of the Pressure-Induced Mott Transition

Abstract

The problem of the Mott insulator¹ and its transition into a metallic state (the Mott transition) is considered to be one of the most serious challenges to the prevailing concepts of solid state physics. At present it remains an unsolved problem. The subject of Mott insulators began in 1937 when De Boer and Verwey² presented their experimental results on the electrical conductivity of transition-metal (TM) oxides (the oxides of Ni, Co, Mn and Fe). The fact that the majority of these oxides were insulators did not fit the conventional Bloch-Wilson band picture. Assuming the compounds were highly ionic would imply partially filled 3d bands and therefore be metallic! In discussion that followed Peierls suggested that the Coulomb repulsion was responsible for the 3d-electron localization. The TM-oxides such as NiO, CoO and MnO are classic examples of Mott insulators (MI). The phenomenological aspects of a MI can be described as follows: It is an antiferromagnetic insulator whose local moments persist unchanged above T_N.