The experimental determination of exchange mass terms in surface states on both terminations of MnBi4Te7

TL;DR

This study measures and compares the exchange and hybridization mass terms in surface states of MnBi4Te7 films with different terminations, revealing key insights into their electronic structure relevant for topological states.

Contribution

It provides the first experimental determination of surface state mass terms on both terminations of MnBi4Te7 using scanning tunneling spectroscopy and magnetic-field-dependent analysis.

Findings

Hybridization gap of ~23 meV on Bi2Te3 termination

Exchange mass term of ~30 meV on MnBi2Te4 termination

Mass term varies with magnetic field and doping levels

Abstract

The intrinsic antiferromagnetic topological insulators in the Mn-Bi-Te family, composed of superlattice-like MnBi2Te4/(Bi2Te3)n (n = 0, 1, 2, 3...) layered structure, present intriguing states of matter such as quantum anomalous Hall effect and the axion insulator. However, the surface state gap, which is the prerequisite for the observation of these states, remains elusive. Here by molecular beam epitaxy, we obtain two types of MnBi4Te7 films with the exclusive Bi2Te3 (BT) or MnBi2Te4 (MBT) terminations. By scanning tunneling spectroscopy, the mass terms in the surface states are identified on both surface terminations. Experimental results reveal the existence of a hybridization gap of approximately 23 meV in surface states on the BT termination. This gap comes from the hybridization between the surface states and the spin-split states in the adjacent MBT layer. On the MBT termination, an exchange mass term of about 30 meV in surface states is identified by taking magnetic-field-dependent Landau level spectra as well as theoretical simulations. In addition, the mass term varies with the field in the film with a heavy BiMn doping level in the Mn layers. These findings demonstrate the existence of mass terms in surface states on both types of terminations in our epitaxial MnBi4Te7 films investigated by local probes.