Landau-Level Quantization and Band Splitting of FeSe Monolayers Revealed by Scanning Tunneling Spectroscopy

TL;DR

This study uses scanning tunneling spectroscopy to reveal Landau-level quantization and band splitting in FeSe monolayers, demonstrating the influence of Rashba spin-orbit coupling on their electronic structure.

Contribution

It provides direct experimental evidence of Rashba SOC effects in FeSe monolayers and introduces a theoretical model explaining the observed Landau quantization behavior.

Findings

Observation of $E_n\propto(nB)^{4/3}$ Landau quantization

Identification of nonparabolic electron bands at X/Y points

Theoretical model highlighting the dominance of the k$^4$-term

Abstract

Two-dimensional (2D) superconductors that reside on substrates must be influenced by Rashba spin-orbit coupling (SOC). The intriguing effect of Rashba-type SOCs on iron-based superconductors (IBSs) has remained largely a mystery. In this work, we unveil modified Landau-level spectroscopy and the intricate band splitting of FeSe monolayers through the precision of scanning tunneling spectroscopy, which unequivocally demonstrates the presence of Rashba SOC. The discovery sheds light on a nonparabolic electron band at the X/Y point, displaying a distinctive Landau quantization behavior characterized by $E_n\propto(nB)^{4/3}$. The theoretical model aligns with our experimental insights, positing that the k$^4$-term of the electron band becomes predominant and profoundly reshapes the band structure. Our research underscores the pivotal role of the Rashba SOC effect on 2D superconductors and sets the stage to probe new quantum states in systems with remarkably low carrier concentrations.