Creation and manipulation of quasi-two-dimensional high-conductivity interfaces of ferroelectric/dielectric heterostructures

The creation of quasi-two-dimensional electron gas at the interface and the ability to control such states by magnetic and electric fields is impossible without the use of new design interfaces. A high-mobility electron gas is observed at the interface of heterostructure LaAlO3 and SrTiO3 when the number of LaAlO3 layers is larger than three [1]. Such a system undergoes a transition to a superconducting state at temperature 300 mK [1].

We investigate the properties of quasi-two-dimensional electron gas (2DEG) at the interface between ferroelectric oxide and insulating oxide in heterostructures BaTiO3/LaMnO3 on LaMnO3 single crystal and in heterostructures Ba0.8Sr0.2TiO3/LaMnO3/Ba0.8Sr0.2TiO3 on MgO substrate. Previously the numerical simulations of the structural and electronic characteristics of the BaTiO3/LaMnO3 interface have been performed. The conductivity and photoconductivity properties had been studied for these heterostructures. For both of heterostructures it was found experimentally that in the samples with polarization of ferroelectric film directed perpendicular to the surface, below certain temperature the electrical resistance exhibits metallic-like behavior. Thus, the evidence of a transition to the state with 2DEG at the interface is demonstrated. The effect of a light on BSTO/LMO interface had been investigated. The resistivity properties of the interface BSTO/LMO interface greatly change under uniform illumination incident on the surface of the ferroelectric film, exhibiting negative photoconductive properties. The effect of metallic conductivity is explained by the discontinuity of ferroelectric polarization. Negative photoconductive can be associated with partial screening of the ferroelectric polarization by photogenerated charge carriers causes the reduction of the carrier concentration at the interface. Measurements in the Kelvin mode of atomic force microscopy showed that illumination has a similar effect on the surface charge concentration, which confirms our hypothesis.

The reported study was funded by Russian Scientific Foundation, research project No. 21-12-00179.

References

1. N. Reyren, et.al, Science 317, 1196 (2007).