We report X-band EPR and 125Te and 77Se NMR measurements on single-crystalline superconducting FeSe0.42Te0.58 (Tc = 11.5(1) K). The data provide evidence for the coexistence of intrinsic localized and itinerant electronic states. In the normal state, localized moments couple to itinerant electrons in the Fe(Se,Te) layers and affect the local spin susceptibility and spin fluctuations. Below Tc, spin fluctuations become rapidly suppressed and an unconventional superconducting state emerges in which 1/T1 is reduced at a much faster rate than expected for conventional s- or s±-wave symmetry. We suggest that the localized states arise from the strong electronic correlations within one of the Fe-derived bands. The multiband electronic structure together with the electronic correlations thus determine the normal and superconducting states of the FeSe1−xTex family, which appears much closer to other high-Tc superconductors than previously anticipated.
@article{arxiv.1006.3411,
title = {Two-electronic component behavior in the multiband FeSe$_{0.42}$Te$_{0.58}$ superconductor},
author = {D. Arcon and P. Jeglic and A. Zorko and A. Potocnik and A. Y. Ganin and Y. Takabayashi and M. J. Rosseinsky and K. Prassides},
journal= {arXiv preprint arXiv:1006.3411},
year = {2011}
}