A Van der Waals Material Exhibiting Room Temperature Broken Inversion Symmetry with Ferroelectricity.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Van der Waals 2D indium selenide has five known polymorphs since its initial synthesis in 1957.
• Exploring new phases is crucial for understanding and exploiting the properties of low-dimensional materials.

Purpose of the Study:

• To report a novel phase of indium selenide synthesized in large-area films.
• To characterize the atomic structure and physical properties of this new phase.
• To investigate its potential for electronic and optical applications.

Main Methods:

• Synthesis of large-area indium selenide films.
• Structural analysis using Scanning Transmission Electron Microscopy (STEM).
• Investigation of electrical polarization via electric-field-induced switching.
• Characterization of nonlinear optical phenomena using Second Harmonic Generation (SHG).

Main Results:

• Identification of a unique ${\beta }^p$ phase with quintuple layers and a distinct zigzag atomic configuration.
• Observation of intralayer shifting within the ${\beta }^p$ layers.
• Demonstration of electric-field-induced switchable polarization, indicating ferroelectricity.
• Experimental evidence of nonlinear optical phenomena (SHG), confirming broken inversion symmetry.

Conclusions:

• The newly discovered ${\beta }^p$ phase of indium selenide exhibits ferroelectricity at room temperature.
• This phase holds promise for applications in low-dimensional electronic and optoelectronic devices.
• The findings expand the known family of indium selenide materials and their functionalities.