Superconducting Phase Diagrams of LuB₁₂ and Lu_1-xZr_xB₁₂ (x≤0.45) down to 50 mK

Abstract

Lutetium dodecaboride LuB 12 is a simple weak-coupling BCS superconductor with critical temperature T c ≈ 0.42 K, whilst ZrB 12 is a strong-coupling BCS superconductor with the highest critical temperature T c ≈ 6.0 K among this group of materials. In case of lutetium substitution by zirconium ions in LuB 12 the crossover from weak-to strong-coupling superconductor can be studied. We have investigated the evolution of critical temperature T c and critical field H c in high-quality single crystalline superconducting samples of Lu 1-x Zr x B 12 (0 ≤ x  0.45) by measuring magnetic ac-susceptibility between ≈ 1 K and 50 mK. To obtain this kind of experimental data, a new susceptometer was designed, constructed and tested, which can work in a wide temperature range of 0.05 K -3 K in 3 He-4 He dilution refrigerator. The measurements with this new susceptometer revealed how T c (x) and H c (x) increases with increasing concentration of zirconium in Lu 1-x Zr x B 12 solid solutions as well as how their superconducting phase diagram develops.

Inhomogeneous superconductivity in LuxZr1−xB12 dodecaborides with dynamic charge stripes

“…Lebedev Physical Institute of RAS in the temperature range 0.3 -300 K and in magnetic fields up to 9 T. Field and temperature dependences of magnetization were recorded by a Quantum Design MPMS-5. To measure the magnetic characteristics down to very low temperatures (~50 mK) an original acsusceptometer based in a dilution 3 He - 4 He mini-refrigerator was applied [49]. For measurements of resistivity and Hall effect we used an original setup described in [50].…”