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

Abstract

The discovery of a two-dimensional electron gas (2DEG) at the $$\hbox {LaAlO}_3/\hbox {SrTiO}_3$$ LaAlO 3 / 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 $$\hbox {KTaO}_3$$ KTaO 3 , $$\hbox {BaTiO}_3$$ 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.