High Quality Fe_1+yTe Synthesized by Chemical Vapor Deposition with Conspicuous Vortex Flow

2D materials provide an ideal platform to explore novel superconducting behavior including Ising superconductivity, topological superconductivity and Majorana bound states in different 2D stoichiometric Ta-, Nb-, and Fe-based crystals. However, tuning the element content in 2D compounds for regulating their superconductivity has not been realized. In this work, the synthesis of high quality Fe_1+yTe with tunable Fe content by chemical vapor deposition (CVD) is reported. The quality and composition of Fe_1+yTe are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). The superconducting behavior of Fe_1+yTe crystals with varying Fe contents is observed. The superconducting transition of selected Fe_1.13±0.06Te sample is sharp (ΔT_c = 1 K), while Fe_1.43±0.07Te with a high-Fe content shows a relative broad superconducting transition (ΔT_c = 2.6 K) at zero magnetic field. Significantly, the conspicuous vortex flow and a transition from a 3D vortex liquid state to a 2D vortex liquid state is observed in Fe_1.43±0.07Te sample. This work highlights the tunability of the superconducting properties of Fe_1+yTe and sheds light on the vortex dynamics in Fe-based superconductors, which facilitates them to understand the intrinsic mechanisms of high-temperature superconductivity.