Spectral weight reduction of two-dimensional electron gases at oxide surfaces across the ferroelectric transition

P Jaiban,R Yimnirun,A Watcharapasorn,R.-H He,S Chaiyachad,Z.-X Shen,S H Yao,T Eknapakul,W Meevasana,S Maensiri,S Siriroj,H Y Hwang,Y Tokura,M Unruan,S.-K Mo,N Pisitpipathsin,M.-H Lu

doi:10.1038/s41598-020-73657-1

Abstract

The discovery of a two-dimensional electron gas (2DEG) at the hbox {LaAlO}_3/hbox {SrTiO}_3 interface has set a new platform for all-oxide electronics which could potentially exhibit the interplay among charge, spin, orbital, superconductivity, ferromagnetism and ferroelectricity. In this work, by using angle-resolved photoemission spectroscopy and conductivity measurement, we found the reduction of 2DEGs and the changes of the conductivity nature of some ferroelectric oxides including insulating Nb-lightly-substituted hbox {KTaO}_3, hbox {BaTiO}_3 (BTO) and (Ca,Zr)-doped BTO across paraelectric-ferroelectric transition. We propose that these behaviours could be due to the increase of space-charge screening potential at the 2DEG/ferroelectric regions which is a result of the realignment of ferroelectric polarisation upon light irradiation. This finding suggests an opportunity for controlling the 2DEG at a bare oxide surface (instead of interfacial system) by using both light and ferroelectricity.

Highlights

The discovery of a two-dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 interface has set a new platform for all-oxide electronics which could potentially exhibit the interplay among charge, spin, orbital, superconductivity, ferromagnetism and ferroelectricity
There were theoretical predictions that 2DEG states, which are formed at the interface between a ferroelectric oxide and SrTiO3, can be controlled via ferroelectric p olarisation[21,22]; experimentally, the control of 2DEG conductivity by using ferroelectric polarisation was observed in the modified structure of ferroelectric Pb(Zr0.2 Ti0.8)O3/LaAlO3 /SrTiO3 13 and LaAlO3/Ba0.2 Sr0.8 TiO3 23 and the modified surface of SrTiO3 24,25
We proposed that irradiating the light on the ferroelectric state-oxide surfaces can align the ferroelectric polarisation through the excess of charge carriers which is not expected to occur in the paraelectric state

Summary

Introduction

The discovery of a two-dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 interface has set a new platform for all-oxide electronics which could potentially exhibit the interplay among charge, spin, orbital, superconductivity, ferromagnetism and ferroelectricity. By using angle-resolved photoemission spectroscopy and conductivity measurement, we found the reduction of 2DEGs and the changes of the conductivity nature of some ferroelectric oxides including insulating Nb-lightlysubstituted KTaO3 , BaTiO3 (BTO) and (Ca,Zr)-doped BTO across paraelectric-ferroelectric transition. We propose that these behaviours could be due to the increase of space-charge screening potential at the 2DEG/ferroelectric regions which is a result of the realignment of ferroelectric polarisation upon light irradiation. There were theoretical predictions that 2DEG states, which are formed at the interface between a ferroelectric oxide and SrTiO3 , can be controlled via ferroelectric p olarisation[21,22]; experimentally, the control of 2DEG conductivity by using ferroelectric polarisation was observed in the modified structure of ferroelectric Pb(Zr0.2 Ti0.8)O3/LaAlO3 /SrTiO3 13 and LaAlO3/Ba0.2 Sr0.8 TiO3 23 and the modified surface of SrTiO3 24,25

Methods

Results

Conclusion