Unusual Hole and Electron Midgap States and Orbital Reconstructions Induced Huge Ferroelectric Tunneling Electroresistance in BaTiO₃/SrTiO₃

Abstract

Oxide heterostructures have attracted a lot of interest because of their rich exotic phenomena and potential applications. Recently, a greatly enhanced tunneling electroresistance (TER) of ferroelectric tunnel junctions (FTJs) has been realized in such heterostructures. However, our understanding on the electronic structure of resistance response with polarization reversal and the origin of huge TER is still lacking. Here, we report on electronic structures, particularly at the interface and surface, and the control of the spontaneous polarization of BaTiO 3 films by changing the termination of a SrTiO 3 substrate. Interestingly, unusual electron and hole midgap states are concurrently formed and accompanied by orbital reconstructions, which determine the ferroelectric polarization orientation in the BaTiO 3 /SrTiO 3 . Such unusual midgap states, which yield a strong electronic screening effect, reduce the ferroelectric barrier width and height, and pin the ferroelectric polarization, lead to a dramatic enhancement of the TER effect. The midgap states are also observed in BaTiO 3 films on electrondoped Nb/SrTiO 3 revealing its universality. Our result provides new insight into the origin of the huge TER effect and opens a new route for designing ferroelectric tunnel junction-based devices with huge TER through interface engineering.

Emergent properties at oxide interfaces controlled by ferroelectric polarization

“…1. These heterointerfaces sometimes exhibit intriguing physical properties, such as superconductivity 12,13 , the tunneling electroresistance (TER) effect [14][15][16] , and highmobility charge-carrier gases 17 , which exceed the limitations of chemical contraindication in bulk materials 18 . In addition, polarization can be used as a "switch" to control the physical state (i.e., electric or magnetic properties) at the heterointerface; this is referred to as the "polar gating" effect [19][20][21][22][23][24] .…”

Low-Temperature Tunneling Electroresistance in Ferromagnetic Metal/Ferroelectric/Semiconductor Tunnel Junctions

“…Memristors are ideal building blocks for brain-inspired neuromorphic computing. − The recent discovery has shown that ferroelectric tunnel junctions (FTJs) have great potential to be used in nonvolatile data storage devices and in the newly emerged brain-inspired computing devices due to their interesting memristive characteristics. − A traditional FTJ device is made up of two metal electrodes (Au, Co, Fe, Ag, etc.) and an ultrathin ferroelectric layer (BaTiO 3 , BiFeO 3 , PVDF, etc.)…”

Observation of strong helical excitons and unexpectedly giant Rashba splitting in single crystal two-dimensional Organic-Inorganic Halide Perovskites

“…S1). In the extreme case where n=∞, the structure becomes a three-dimensional perovskite similar to BaTiO3 [25][26][27][28] .…”