2019/08/21 by Qiang Zou, Zou, Qiang, Mingming Fu +11
Materials Science · Physics and Astronomy · #Iron-based superconductors research #Physics of Superconductivity and Magnetism #Rare-earth and actinide compounds
paper · pdf · doi:10.48550/arxiv.1908.10436
The electronic structure inhomogeneities in Co, Ni, and Cr doped BaFe2As2 122\nsingle crystals are compared using scanning tunneling microscopy/spectroscopy\n(STM/S) at the nanoscale within three bulk property regions in the phase\ndiagram: a pure superconducting (SC) dome region (Co-122), a coexisting SC and\nantiferromagnetic (AFM) region (Ni-122), and a non-SC region (Cr-122). Machine\nlearning is utilized to categorize the various nanometer scale inhomogeneous\nelectronic states, described here as in-gap, L-shape and S-shape states\nimmersed into the SC matrix for Ni-and Co-doped 122, and L-shape and S-shape\nstates into the metallic matrix for Cr-doped 122. Although the relative\npercentages of in-gap, L-shape and S-shape states vary in the three samples,\nthe total volume fraction of the three electronic states is quite similar. This\nis coincident with the number of electrons (Ni0.04 and Co0.08) and holes\n(Cr0.04) doped into the 122 compound. By combining the volume fractions of the\nthree states, the local density of states (LDOS), magnetic field dependent\nbehavior and global properties in these three samples, the in-gap state is\nconfirmed as a magnetic impurity state from the Co or Ni dopants. In addition,\nthe L-shape state is identified as a spin density wave (SDW) which competes\nwith the SC phase, and the S-shape state is found to be another form of\nmagnetic order which constructively cooperates with the SC phase, rather than\ncompeting with it. The comparison of the vortex structures indicates that the\ninhomogeneous electronic states serve as pinning centers for stabilizing the\nvortex lattice.\n