Physical properties of HgBa₂Ca₂Cu₃O₈ with T_c ≈ 133K

Abstract

Several samples containing HgBa2Ca2Cu3O8+δ (Hg-1223) as the main phase have been investigated. Specificheat Cp(T) data measured on our samples with largest volume fraction Hg-1223 (≈60%) show a distinct discontinuity ΔCp/Tc ≈ 27 mJ/mole K2 at Tc. From measurements of the reversible magnetization M(H,T) in the mixed state, we obtain approximate values for the London penetration depth λab(0), for the coherence length ξab(0), for the lower and the upper critical fields Hc1,c(0), respectively, and for the Ginzburg-Landau parameter κ, for external fields H//c axis. The location of the irreversibility line in the B-T phase diagram allows us to estimate the anisotropy ratio γ=λc/λab, while magnetization-loop data taken in the irreversible part of mixed state give information about the critical-current densities jc to be expected in Hg-1223. Tunneling-conductance investigations with a scanning-tunneling microscope give a gap value Δ≈24 meV at T=4.2 K. © 1994.