Doping effects on electronic states in electron-doped FeSe: Impact of self-energy and vertex corrections

Abstract

The pairing glue of high-$T_{\mathrm{c}}$ superconductivity in heavily electron-doped (e-doped) FeSe, in which hole-pockets are absent, has been an important unsolved problem. Here, we focus on a heavily e-doped bulk superconductor Li${}_{1-x}$Fe${}_x$OHFeSe ($T_{\mathrm{c}}\sim 40$K). We construct a multiorbital model beyond the rigid band approximation and analyze the spin and orbital fluctuations by taking both vertex corrections (VCs) and self-energy into consideration. Without e-doping ($x=0$), the ferro-orbital order without magnetism in FeSe is reproduced by the VCs.The orbital order quickly disappears when the hole-pocket vanishes at $x\sim 0.03$. With increasing $x$ further, the spin fluctuations remain small, whereas orbital fluctuations gradually increase with $x$ due to the VCs. The negative feedback due to the self-energy is crucial to explain experimental phase diagram. Thanks to both vertex and self-energy corrections, the orbital-fluctuation-mediated $s_{++}$-wave state appears for a wide doping range, consistent with experiments.

10 pages, 8 figures

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• Unconventional density waves and superconductivities in Fe-based superconductors and other strongly correlated electron systems
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