Emergence of ferroelectric topological insulator as verified by quantum Hall effect of surface states in (Sn,Pb,In)Te films

TL;DR

This study reports the experimental observation of a ferroelectric topological insulator phase in (Sn,Pb,In)Te films, characterized by quantum Hall states indicating topological surface states influenced by ferroelectricity.

Contribution

First experimental verification of ferroelectric topological insulator phase via quantum Hall effect in (Sn,Pb,In)Te films with controlled Fermi levels.

Findings

Observation of quantum Hall states with filling factors 1, 2, 3

Identification of ferroelectricity-induced topological surface states

Electronic states are two-dimensional with a single Dirac cone

Abstract

Emergent phenomena arising from nontrivial band structures based on topology and symmetry have been attracting keen interest in contemporary condensed-matter physics. Materials such as SnTe and PbTe are one such example, which demonstrate a topological phase transition while showing ferroelectric instability derived from their rock-salt structure. The ferroelectricity can lift the valley degeneracy, enabling the emergence of the Z2 topological insulator phase, although its observation in transport phenomena remains elusive. Here, we report magnetotransport properties of ferroelectric (Sn,Pb)Te thin films with finely-controlled Fermi levels via In doping. We identified the ferroelectric topological insulator phase from the observations of the quantum Hall states with filling factors of $\nu$ = 1, 2 and 3 with both spin- and valley-degeneracy lifting. The electronic states are two-dimensional, indicating the ferroelectricity-induced topological surface states with a single Dirac cone. The finding of the new topological state with ferroelectricity will further expand the field of topological physics and advance the development of functional properties, such as topological nonlinear photonics and nonreciprocal transport with memory effect.