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

Author:

Kim Jae-Joon12ORCID,Park Min Seok1,Lee Kyoung Seok12,Joo Sang Hyun12,Yoo Jung Hoon1,Bhoi Dilip3ORCID,Min Byeong Hun3,Kim Kee Hoon3,Lee Jinho1

Affiliation:

1. Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea

2. Samsung Electronics Semiconductor R&D Center, Hwaseong-si 18448, Gyeonggi-do, Republic of Korea

3. Center for Novel States of Complex Materials Research, Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea

Abstract

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 × 1 surface reconstructions. On a Ca/La layer on top of an FeAs layer, a clear SC gap of ~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.

Funder

National Research Foundation of Korea

Institute of Applied Physics of Seoul National University

Institute for Basic Science in Korea

NRF

Ministry of Science and ICT

Publisher

MDPI AG

Subject

General Materials Science,General Chemical Engineering

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