Possible unconventional superconductivity in substituted BaFe${}_2$As${}_2$ revealed by magnetic pair-breaking studies

Abstract

The possible existence of a sign-changing gap symmetry in BaFe${}_2$As${}_2$-derived superconductors (SC) has been an exciting topic of research in the last few years. To further investigate this subject we combine Electron Spin Resonance (ESR) and pressure-dependent transport measurements to investigate magnetic pair-breaking effects on BaFe${}_{1.9}{M}_{0.1}$As${}_2$ ($M=$ Mn, Co, Cu, and Ni) single crystals. An ESR signal, indicative of the presence of localized magnetic moments, is observed only for $M=$ Cu and Mn compounds, which display very low SC transition temperature ($T_c$) and no SC, respectively. From the ESR analysis assuming the absence of bottleneck effects, the microscopic parameters are extracted to show that this reduction of $T_c$ cannot be accounted by the Abrikosov-Gorkov pair-breaking expression for a sign-preserving gap function. Our results reveal an unconventional spin- and pressure-dependent pair-breaking effect and impose strong constraints on the pairing symmetry of these materials.

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• Magnetoresistance near a quantum critical point
• Hydrostatic and uniaxial pressure tuning of iron-based superconductors: Insights into superconductivity, magnetism, nematicity and collapsed tetragonal transitions
• Towards a quantitative description of tunneling conductance of superconductors: application to LiFeAs
• Possible unconventional superconductivity in substituted BaFe${}_2$As${}_2$ revealed by magnetic pair-breaking studies
• Anisotropic magnetic excitations and incipient Néel order in Ba(Fe${}_{1-x}$Mn${}_x$)${}_2$As${}_2$
• Scanning tunneling spectroscopy as a probe of multi-Q magnetic states of itinerant magnets
• Orbital localization and the role of the Fe and As $4p$ orbitals in BaFe${}_2$As${}_2$ probed by XANES
• Putative hybridization gap in CaMn${}_2$Bi${}_2$ under applied pressure
• Magnetotransport properties in the magnetic phase of BaFe${}_{2-x}$T${}_x$As${}_2$ (T = Co,Ni): A magnetic excitations approach
• The role of magnetic excitations in magnetoresistance and Hall effect of slightly TM-substituted BaFe${}_2$As${}_2$ compounds (TM = Mn, Cu, Ni)