BCCMS  /  Groups  /  CMS  /  People - Bremen  /  Y. Liang
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Dr. Yan Liang

Field of InterestTD-DFT Charge Dynamics, Photocatalysis, 2D-Materials
PublicationsGoogle Scholar



In view of the above academic significance and my expertise on 2D vdW heterostructures and multilayer multiferroics, I propose to explore the interfacial properties of multilayer ferroelectrics constituted by well-understood 2D vdW single-layers, where the layer stacking and optically controlled properties are yet to be clarified for different device applications. The successful isolation of 2D monolayers with characteristics of semiconducting (MoS2, Ti2CO2, InSe etc.), topological (graphene, Bi2Te3, WTe2 and Na3Bi) and magnetism (MXene, VS2, CrI3, Cr2Ge2Te6 etc.) would add a new area for interface and device engineering. Multilayer 2D materials in the context of ferroelectric phases remain less explored from a fundamental perspective and provide us a unique opportunity to understand the basic physics, potentially emergent phenomena and external stimuli effects at these interfaces. The overarching goal of the project will be use ab initio approaches to clarify the properties (electric/spin polarization, ferroelasticity, ferrovalley, band topology, photoexcitation dynamics and so on) of different multilayer ferroelectric materials by direct characterization or targeted design (see Fig.1a), and uncover the effects of external stimuli on tailoring these interlayer interactions (such as laser excitation, carrier doping and pressure).

The photoexcitation dynamics plays a key role in determining the properties of van der Waals heterostructures (vdWHs). Based on the time-dependent density functional theory combined with nonadiabatic molecular dynamics, we investigate the charge transfer in Janus-MoSSe/WS2 vdWHs. Ultrafast charge separation is observed, arising from the large overlapping between the donor and acceptor states. While the electron–hole recombination is 2 orders of magnitude slower than the charge separation, this can be understood by the fact that the initial and final states are strictly confined to different materials. Additionally, photoresponsivity performance of the vdWHs is also evaluated using density functional theory combined with the nonequilibrium Green’s functions. Simulated results of high photoresponsivity in a broad range of the spectrum endows proposed systems powerful potential in optoelectronic and photovoltaic applications. The atomistic picture revealed in our work provides chemical guidelines and facilitates the design of next-generation devices for light detecting and harvesting.

2D intercorrelated ferroelectrics, exhibiting a coupled in-plane and out-of-plane ferroelectricity, is a fundamental phenomenon in the field of condensed-mater physics. The current research is based on the paradigm of bi-directional inversion asymmetry in single-layers, which restricts 2D intercorrelated ferroelectrics to extremely few systems. Herein, we propose a new scheme for achieving 2D intercorrelated ferroelectrics using van der Waals (vdW) interaction, and apply this scheme to a vast family of 2D vdW materials. Using first-principles, we demonstrate that 2D vdW multilayers, for exam- ple, BN, MoS2, InSe, CdS, PtSe2, TI2O, SnS2, Ti2CO2 etc., can exhibit coupled in-plane and out-of-plane ferroelectricity, thus yielding 2D intercorrelated ferroelectric physics. We further predict that such intercorrelated ferroelectrics could demonstrate many distinct properties, for example, electrical full control of spin textures in trilayer PtSe2 and electrical permanent control of valley-contrasting physics in four-layer VS2. Our finding opens a new direction for 2D intercorrelated ferroelectric research.