Observations of Nematicity, Dopants, and Zero-Bias Conductance Peaks for the Ca0.9La0.1FeAs2 Superconductor

Ca1-xLaxFeAs2 (CLFA112) belongs to a new family of Fe-based superconductors (FeSCs) and has a unique crystal structure featuring an arsenic zigzag chain layer, which has been proposed to be a possible two-dimensional topological insulator. This suggests that CLFA112 is a potential topological superconductor-a platform to realize Majorana fermions. Up to now, even a clear superconducting (SC) gap in CLFA112 has never been observed, and the SC properties of CLFA112 remain largely elusive. In this letter, we report the results of an atomic-scale investigation of the electronic structure of CLFA112 crystals using low-temperature scanning tunneling microscopy (STM). We revealed four different types of surfaces exhibiting distinct electronic properties, with all surfaces displaying dominating 2 x 1 surface reconstructions. On a Ca/La layer on top of an FeAs layer, a clear SC gap of similar to 12 mV was observed only at the crevices (vacancies) where the FeAs layer can be directly accessed. Remarkably, the FeAs termination layer displayed a dispersing nematic modulation both in real and q space. We also present peculiar zero-bias conductance peaks for the very As chain layer that is believed to exhibit a topological edge state as well as the influence of La dopants on the As chain layer.

Automated summary

In this study, the electronic structure of CLFA112 crystals was investigated at the atomic scale using low-temperature scanning tunneling microscopy (STM). Four different types of surface reconstructions were observed on CLFA112 crystals, and a clear superconducting gap was observed only at certain crevices on the surface. The FeAs layer exhibited a dispersing nematic modulation, and peculiar zero-bias conductance peaks were observed in the arsenic chain layer along with the influence of La dopants.