The possibility of fluctuation superconductivity in the mercury chain compound Hg_3-δAsF₆

The zero-field diamagnetic susceptibility and the paraconductivity of the mercury chain compound Hg_{3- delta}AsF₆are calculated using the anisotropic Ginzburg-Landau theory with a model BCS hamiltonian with only inter-chain coupling. Thecoherence lengths are calculated from both the correlation function of Cooper pairs andthe mean-field-type BCS hamiltonian with Cooper pairs hopping only in the c direction. Theauthors consider two limiting conditions: The ‘superclean’ limit, in which the correlation length in the c direction is given by xi _c(0) approximately=h(cross) upsilon _F^c/pi Delta; and the two-dimensional (2D) limit, in which weak scattering reduces xi _c to approximately a lattice constant. In the2D limit the susceptibility chi _c for a field in the c direction, i.e. perpendicular to the chains, gives a Meissner effect of about 20% at T=2.72 T_c, whereT_c=0.3 K, under a pressure of 10 kbar. This may partly account for the large Meissner effect observed in Hg_{3- delta} AsF₆in the temperature range T_c-10T _c. The paraconductivity is extremely small near T_c.