Torque measurements on methylene blue intercalation compounds of 2H-TaS 2

Abstract

The superconducting properties in high magnetic fields of three different methylene blue intercalation compounds of 2H-TaS 2 (compounds with 9å, 12å and 17å layer separation) are measured with a torquemeter. The superconducting magnetisation curves can be separated in two parts, a reversible part at high fields and an irreversible part at low fields, defining an irreversibility line as in the organic or high-T c superconductors. The angular dependence of H c2 of the 9å compound can be fitted by the anisotropic Ginzburg-Landau theory giving an anisotropy factor of about 60. The T c values of these compounds are 3.8 K for the 17å, 5. l K for the 12å and 5. l K or 4.6K (depending on the cooling rate) for the 9å compound, tested by ac-susceptibility. The estimated critical field of dimensional crossover is out of the measured temperature range and cannot be seen in this work.