2D ferroelectric and ferromagnetic materials discovered in the recent decade have opened a new era for the construction and tuning of heterostructures for electronic and computing applications. Semiconducting 2D ferroic materials are especially interesting as their electronic structures deeply intertwine with the spontaneously broken symmetry, thus new freedoms like spin, orbital and electronic valleys are generated. In this talk, I will mainly focus on the development of group-IV monochalcogenide 2D ferroelectric semiconductors, from the discovery, ferroelectric mechanism, spin-valley correlation in the electronic structures, to the recently realized 2D lateral heterostructures and superlattices. The most interesting advancement is the design and in situ molecular beam epitaxial growth of a new type of valley-controlled ferroelectric sandwich heterostructure that is analogous to the classical spin valve, in which the transmission probability of electronic states is determined by the alignment of the polarization of two ferroic layers separated by a thin barrier. The mechanism of this ferroelectric valley valve relies on the polarization-tuned hole valleys in group-IV monochalcogenide ferroelectric semiconductors. The creation of such device is enabled by our ability of precisely controlling the growth mode of these materials, which eventually generates SnTe-PbTe monolayer superlattices with 2-nm wide material section, the narrowest ever 2D lateral superlattices to the best of our knowledge. Based on such structures, we plan to further develop novel non-volatile logic and storage devices, as well as topological qubits.
Biography: Kai Chang obtained his Ph.D. in 2015 from Tsinghua University, focusing on the molecular beam epitaxial growth and scanning tunneling microscopy characterization of low-dimensional quantum materials. He worked as a postdoctoral staff in Max Planck Institute of Microstructure Physics from 2015 to 2019, and then joined Beijing Academy of Quantum Information Sciences (BAQIS) by the end of 2019. He is currently the executive president of BAQIS and the Principal Investigator of the Low-Dimensional Quantum Materials Team. His research focuses on the molecular beam epitaxial growth and scanning tunneling microscopy characterization of 2D ferroic heterostructures, involving the combinations of 2D ferroelectrics, ferromagnets, superconductors and semiconductors, particularly on the design and construction of novel non-volatile logic/memory devices and topological qubits based on 2D ferroic semiconductors