single crystals

FeSe has the simplest crystal structure among Fe-based superconductors with a superconducting transition at T_C ~ 9 K and a nematic transtion at T_S ~ 90 K. By replacing 60% of Se with Te, FeSe_1-xTe_x (x=0.6), T_C increases up to 14 K and the superconducting gap structure changes from nodal to full-gap with the disappearance of the nematic phase transition. This system is therefore an ideal playground to understand the relationship between superconductivity and electronic nematicity in Fe-based superconductors. However, a difficulty in single-crystal growth in the phase-separation region (0<x<0.5) so far prevent a full understanding of the system [1]. We successfully grew single crystals in this region and performed electronic transport and low-temperature scanning tunneling microscopy and spectroscopy measurements on these crystals. The details will be discussed in the presentation. [1] M. Fang et al., PRB 78, 224503 (2008).