Peculiar Switchable Out-of-Plane Electronic Polarization in 2D material


Ultrathin films are simply films grown using complex chemical and physically deposition techniques that are used in a variety of technologically advanced applications and measure less than 50 nanometers. To date, controlling electric dipoles in the ultrathin films has remained a key challenge due to the finite screening length of surface charges. This shortcoming can be attributed to the depolarization field, which tends to become more important as the ferroelectric film thickness is reduced. In a recent publication, a novel covalent-polar semiconductors have been reported by developing from a physical understanding of 3D hyperferroelectric. It shows an intrinsic 2D vertical polarization, consequently presenting new device opportunities. In fact, the aforementioned materials differ from ordinary ferroelectrics in that they are able to maintain polarization normal to a surface even with an unscreened depolarization field. Usually, these derivatives 2D material with broken mirror symmetry have attracted considerable attention consequent to their unique properties; namely, large piezoelectric effect, Rashba spin splitting, and second-harmonic generation response. Unfortunately, a fundamental challenge has plagued further development due to the fact that identifying stable phases that exhibit robust intrinsic 2D vertical polarization remains a challenge.

Therefore, there is a need to further develop the 2D material in order to unlock its full potential. In this context, Jilin University researchers: Dr. Zhun Liu and Professor Lijun Zhang (the leader of Theory & Design of Optoelectronic Semiconductors Group) together with Prof. David J. Singh at the University of Missouri proposed a systematic exploration of the 2D vertical polarization in a single LiAlTe2 atomic quadruple layer (QL) by studying the polar layers in the vdW type β-LiAlTe2. They aspired to develop a novel, yet auspicious phase via computational material design, using 2D LiAlTe2. Their work is currently published in the research journal, Advanced Electronic Materials.

The authors reported that in addition to the expected layered version of bulk LiAlTe2, β-LiAlTe2, a novel 2D structure, γ-LiAlTe2, was found. Furthermore, it was observed that in the reported phase, the vertical dipole could be switched between 0.07 and −0.11 e Å. Additionally, the associated asymmetric double-well energy profile could be continuously tuned by the applied electric field as well as strain.

In summary, the study explored the 2D vertical polarization in a single LiAlTe2 QL by studying the polar layers in the vdW type β-LiAlTe2. Results indicate that the global optimization structure search yields a nonpolar ground state and a series of 2D vertical polarization phases for a single LiAlTe2 QL. In a statement to Advances in Engineering, Professor Lijun Zhang highlighted that their discovered off-plane switch-ability provides an opportunity for a 2D γ-LiAlTe2 based interfacial phase-change memory device; for example, by growing γ-LiAlTe2/GeTe heterostructures.

Peculiar Switchable Out-of-Plane Electronic Polarization in 2D material - Advances in Engineering

About the author

Lijun Zhang is a professor of School of Materials Science and Engineering, Jilin University, China. He is the PI of Theory & Design of Optoelectronic Semiconductors Group. He obtained his B.S. degree at Northeast Normal Univ. (2003), and completed his Ph.D. with Prof. Yanming Ma and Prof. Guangtian Zou at Jilin Univ. (2008). As a postdoctoral researcher, he joined Prof. David J. Singh’s group at Oak Ridge National Laboratory (2008), and moved to Prof. Alex Zunger’s group at National Renewable Energy Laboratory (2010). He then became a research assistant professor at Univ. of Colorado at Boulder (2013). In September 2014, he joined Jilin Univ. as a Professor. He was awarded by the Recruitment Program of Global Youth Experts in China (2014) and the National Science Fund for Outstanding Young Scholars (2017). He is the winner of Computational Materials Science Award of Chinese Materials Research Society (2018) and the winner of the top grade Jilin Province Science and Technology Award for Young Researchers (2018).

His current interests focus on materials by design and band structures engineering of functional semiconductors for optoelectronic applications. He has published nearly 100 peer-reviewed papers (more than 60 of them with him as the first/corresponding author) with more than 4500 citations. The papers with him as the first/corresponding author include Nature Reviews Materials (1), Nature Commun. (6), Phys. Rev. Lett. (2), J. Am. Chem. Soc. (5), Nano Lett. (5), ACS Nano (1), Adv. Funct. Mater. (1), Adv. Sci. (1), Phys. Rev. series (17). The current h-index value is 36. He is the Editorial Board Member of the journals of Nano Research, Scientific Reports, Journal of Semiconductors, Chinese Optics. For more information, see his research webpages: ResearcherID,  GoogleScholar


Zhun Liu, Yuanhui Sun, David J. Singh, Lijun Zhang. Switchable Out-of-Plane Polarization in 2D LiAlTe2. Advanced Electronic Materials 2019, volume 5, 1900089.

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