Scanning Tunneling Spectroscopy and Vortex imaging in High-Tc Superconductors

Yi Yin
Physics Department
Harvard University



A low temperature scanning tunneling microscope (STM) has been applied to two typical high Tc superconductors, cuprates and iron pnictides. For an iron pnictide superconductor, BaFe1.8Co0.2As2, we have used the scanning tunneling spectroscopy (STS) to investigate superconducting gaps and vortices in magnetic fields up to 9 Tesla. Compared to the case in cuprates, the spectra trend is opposite and the spatial gap inhomogenenity is much less in this iron pnictide. Motived by this contradiction, the same STS and vortex imaging technique is applied to a cuprate, Bi2Sr2CuO{6+\delta}. The density of states(DOS) maps at different magnetic fields are analyzed by the normalization method. We distinguish two energy scales that represent the coexisting pseudogap and superconducting order. We conclude that the pesudogap order may contribute to the different apparent gap trend between iron pnictides and cuprates.