Lifthitz Transition and Shadow Gap in Li(Fe1−xCox)As Investigated by STM/STS
- 46 Downloads
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.
KeywordsHigh-Tc superconductor Iron-based superconductor LiFe1−xCoxAs Shadow gap Lifshitz transition Scanning tunneling microscopy
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).
- 5.Dai, Y., Miao, H., Xing, L., Wang, X., Wang, P., Xiao, H., Qian, T., Richard, P., Qiu, X., Yu, W.: Spin-fluctuation-induced non-fermi-liquid behavior with suppressed superconductivity in life 1? x co x as. Phys. Rev. X 5(3), 031035 (2015)Google Scholar
- 9.Ye, Z., Zhang, Y., Chen, F., Xu, M., Jiang, J., Niu, X., Wen, C., Xing, L., Wang, X., Jin, C.: Extraordinary doping effects on quasiparticle scattering and bandwidth in iron-based superconductors. Phys. Rev. X 4(3), 031041 (2014)Google Scholar
- 10.Lifshitz, I.: Anomalies of electron characteristics of a metal in the high pressure region. Sov. Phys. JETP 11(5), 1130–1135 (1960)Google Scholar
- 20.Chi, S., Johnston, S., Levy, G., Grothe, S., Szedlak, R., Ludbrook, B., Liang, R., Dosanjh, P., Burke, S.A., Damascelli, A., Bonn, D.A., Hardy, W.N., Pennec, Y.: Sign inversion in the superconducting order parameter of LiFeAs inferred from Bogoliubov quasiparticle interference. Phys. Rev. B 89(10), 104522 (2014)ADSCrossRefGoogle Scholar
- 25.Yang, H., Wang, Z., Fang, D., Li, S., Kariyado, T., Chen, G., Ogata, M., Das, T., Balatsky, A., Wen, H.H.: Unexpected weak spatial variation in the local density of states induced by individual co impurity atoms in superconducting Na(Fe1−xCo x)As crystals revealed by scanning tunneling spectroscopy. Phys. Rev. B 86(21), 214512 (2012)ADSCrossRefGoogle Scholar