Logarithmic dependence of the low-field magnetoresistance in Hg3-δAsF6

A Fermi surface with a square cross section and slightly rounded corners, which results from perpendicular sets of weakly coupled one-dimensional chains, is found both experimentally and theoretically to lead to a strong enhancement of the low-field magnetoresistance, and a logarithmic dependence on the magnetic field, Δρ(H)ρ(0)H2lnH0H for H<H0, where H0 is a characteristic effective field. The logarithmic dependence is observed for Hg3-δAsF6 in a series of new high-sensitivity experimental results for 0.5<H<40 Oe at a temperature of 4.2 K. Analysis of the data leads to a value for the weak interchain coupling (ΔEEF 6×10-3). Hall-effect data are presented for the temperature range 4.2<T<100 K, and fields up to 4.5 kOe. At low temperatures, the measured Hall coefficient is in agreement with the anisotropic three-dimensional Fermi surface determined earlier by de Haas-van Alphen measurements. The smaller Hall coefficient above 10 K suggests the possibility of a crossover to localization onto families of parallel one-dimensional chains.