Agenda

The multi-gap band structure of iron pnictide superconductors is manifested in multiple phenomena, some of which are still not fully understood.  An anomalous angular dependency of the upper critical field Hc2 has recently been observed [1], deviating from the 3D-anisotropic Ginzburg-Landau (3D-aGL) behavior that would be expected, given the small anisotropy factor or these systems. Using fluctuation-induced magnetoconductivity data just above Tc in Ba(FexCo1-x)2As2 single crystals, a precise, criterion-free determination of Hc2(θ) was made (θ being the angle between the applied field and the crystal c-axis). Our data was then compared with previous theoretical calculations for a superconductor with multiple gaps, supporting the hypothesis of the anomalous Hc2(θ) behavior arising from the multiband structure [2-4].

 

References:

[1] J. Murphy et al., Angular-dependent upper critical field of overdoped Ba(Fe1−xNix)2As2., Phys. Rev. B 87, 094505 (2013)

[2]. A. Gurevich, Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors. Phys. Rev. B 67, 184515 (2003)

[3]. A. Gurevich, Upper critical feld and the Fulde–Ferrel–Larkin–Ovchinnikov transition in multiband superconductors. Phys. Rev. B 82, 184504 (2010)

[4] I. F. Llovo, C. Carballeira, D. Sóñora, A. Pereiro, J. J. Ponte, S. Salem-Sugui Jr., A. S. Sefat and J. Mosqueira, Multiband effects on the upper critical field angular dependence of 122 family iron pnictide superconductors, Sci. Rep. 11, 11526 (2021)