A review of recent ab initio studies on strain-tunable conductivity in tunnel junctions with piezoelectric, ferroelectric and multiferroic barriers

Functional tunnel junctions are promising for developing novel electronic devices due to their combination of quantum-mechanical tunneling and the unique characteristics of a nanometer-thick functional film. Much research has been reported on the nanoscale properties, fabrication methods and applications of tunnel junctions with piezoelectric, ferroelectric, multiferroic barriers both in theory and experiment. The electronic transport properties of functional tunnel junctions can be significantly tuned by means such as switching polarization and applying strain, leading to a giant variation in tunneling electroresistance. Such tunability has been predicted by ab initio studies and verified by experiments, suggesting huge application prospects. In this review, we mainly focus on recent progress in ab initio studies on the strain-tunable transport properties in piezoelectric, ferroelectric and multiferroic tunnel junctions. The main content of this review include an introduction to the physics of the three kinds of tunnel junction and the basic principle of ab initio studies, the physical mechanisms, and important results on the strain-tunable transport properties of tunnel junctions. Prospects and challenges of this field are also highlighted.