Defect-induced weak collective pinning in superconducting YB6 crystals

In a previous study (2017 Phys. Rev. B 96 144501), a strong variation in the superconducting transition temperature T (c) of YB6 differing by a factor of two has been explained by a change in the density of yttrium and boron vacancies tuning the electron-phonon interaction. Here, by using an array of miniature Hall probes, we address the penetration of the magnetic field, pinning, and critical current density on a series of YB6 single crystals with T (c) variation between 4.25 and 7.35 K. The analysis of the superconducting and normal-state specific heat characteristics allowed us to determine T (c) and the stoichiometry of our samples. We observed almost no pinning in the most stoichiometric YB6 crystal with the lowest T (c). Upon increasing the number of vacancies weak pinning appears, and the critical current density is enhanced following the increased transition temperature in a linear variation. We argue that such an increase is, within weak collective pinning theory, consistent with the increasing number of vacancies that serve as pinning centers.

Automated summary

By using an array of miniature Hall probes, the penetration of the magnetic field, pinning, and critical current density on a series of YB6 single crystals with different superconducting transition temperatures has been studied. The stoichiometry and transition temperature were determined by analyzing the specific heat characteristics. It was found that the increase in vacancies leads to enhanced pinning and critical current density, consistent with weak collective pinning theory.