A Study of Fermi Surfaces of ReO₃ and Hg₂.₈₆AsF₆

Abstract

<p>The Fermi surfaces of ReO₃ and Hg₂.₈₆AsF₆ have been studied. Open orbits have been observed in ReO₃ in magnetic fields up to 5.5 T by the induced torque method. The experimental results show that the third band Fermi surface of ReO₃ is connected along the <100> directions as predicted by Mattheiss' augmented-plane-wave band structure calculation. de Haas-van Alphen frequencies of ReO₃ have been measured as a function of pressure up to 5 kbar with the magnetic field along the [111] and [001] crystallographic directions. THe variation of the frequencies with pressure is linear at low pressure and for the α frequencies follows free electron scaling predictions. Above 3 kbar, all cross seotional areas increase much faster with pressure. The area compressibilities are one order of magnitude higher than the low ressure area compressibilities. The Dingle temperature and the g-factor along [111] in ReO₃ were measured as a function of pressure up to 5 kbar. The resistivity of ReO₃ was also measured as a function of pressure at room temperature and at 110 K. The increase in the de Haas-van Alphen frequencies of ReO₃ above 3 kbar may be attributed to an increase in covalent bonding or a rotation of the oxygen atoms at high pressure. Measurement of the de Haas-van Alphen effect, at 1.1 K, in the linear-chain mercury compound Hg₂.₈₆AsF₆ indicates that the Fermi surface consists of a set of cylinders with axes along the c-axis. The multiplicity of cylinders is shown to arise from a translation of the Fermi surface sheets by a superlattice formed by the incommensurate mercury chains.</p>