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Journal of Superconductivity and Novel Magnetism

, Volume 32, Issue 12, pp 3789–3795 | Cite as

Lifthitz Transition and Shadow Gap in Li(Fe1−xCox)As Investigated by STM/STS

  • Ruizhe LiuEmail author
  • Zhiyang Ye
  • Jihui Wang
  • Limin Liu
Original Paper
  • 46 Downloads

Abstract

Recently, APRES experiments reported a superconducting (SC) gap opened on a shallow insulating band in Co-doped LiFeAs (Miao et al. 6:6056, 2015). Theoretically, this particular SC gap is characterized by asymmetric density of states (DOS) and vanishing of SC coherence peak, addressed as shadow gap. Using the scanning tunneling microscopy/spectroscopy (STM/STS), 1% and 3% Co-doped LiFeAs were studied. The Co dopants were atomically resolved. STS results at the Co sites on both samples showed no bound states. Negligible difference between spectra at Co sites and defect-free area was observed, suggesting weak impurity potentials of the Co dopants. Similar to LiFeAs, two SC coherence peaks at Δα = 5.6 meV and Δβ = 2.5 meV were observed in STS spectra of the 1% doped sample, which were the SC gaps of the inner hole band α and the outer hole band β. In the SC state, spectra of 3% Co-doped sample showed a broad peak at E1 = − 7.2 meV and other two peaks at ± 3.9 meV. Above Tc, the peak at E1 shifts to − 4.8 meV, and the peaks at ± 3.9 meV vanish. We showed that the distinct difference of STS results in 1% and 3% Co-doped LiFeAs was caused by Lifthitz transition and shadow gap on the shallow band. By fitting the spectra at low energies, we found the anisotropy of the β band was greatly increased when shadow gap opens on the shallow α band.

Keywords

High-Tc superconductor Iron-based superconductor LiFe1−xCoxAs Shadow gap Lifshitz transition Scanning tunneling microscopy 

Notes

Acknowledgments

This work was supported by the National Natural Science Foundation of China under Grant No. 11227903, Priority Research Program B of Chinese Academy of Sciences under Grant No. Y4VX092X81, and the State of Texas through Texas Center for Superconductivity at University of Houston (TcSUH).

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Authors and Affiliations

  1. 1.Beijing National Laboratory for Condensed Matter Physics, Institute of PhysicsChinese Academy of SciencesBeijingChina
  2. 2.University of Chinese Academy of SciencesBeijingChina
  3. 3.Texas Center for SuperconductivityUniversity of HoustonHoustonUSA

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