A van der Waals material exhibiting room temperature broken inversion symmetry with ferroelectricity

Fabia F. Athena; Cooper A. Voigt; Mengkun Tian; Anjan Goswami; Emily Toph; Moses Nnaji; Fanuel Mammo; Brent K. Wagner; Sungho Jeon; Wenshan Cai; Eric M. Vogel

arXiv · 2510.03977

A van der Waals material exhibiting room temperature broken inversion symmetry with ferroelectricity

Fabia F. Athena·Cooper A. Voigt·Mengkun Tian·Anjan Goswami·Emily Toph·Moses Nnaji·Fanuel Mammo·Brent K. Wagner·Sungho Jeon·Wenshan Cai·Eric M. Vogel

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Abstract

Since the initial synthesis of van der Waals two-dimensional indium selenide was first documented in 1957, five distinct polymorphs and their corresponding polytypes have been identified. In this study, we report a unique phase of indium selenide via Scanning Transmission Electron Microscopy (STEM) analysis in the synthesized large-area films -- which we have named the $\beta^\text{p}$ phase. The quintuple layers of the $\beta^\text{p}$ phase, characterized by a unique zigzag atomic configuration with unequal indium-selenium bond lengths from the middle selenium atom, are distinct from any other previously reported phase of indium selenide. Cross-sectional STEM analysis has revealed that the $\beta^\text{p}$ layers exhibit intralayer shifting. We found that indium selenide films with $\beta^\text{p}$ layers display electric-field-induced switchable polarization characteristic of ferroelectric materials, suggesting the breaking of the inversion symmetry. Experimental observations of nonlinear optical phenomena -- Second Harmonic Generation (SHG) responses further support this conclusion. This study reports a $\beta^\text{p}$ phase of indium selenide showing ferroelectricity over large areas at room temperature in a low-dimensional limit.

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Fabia F. Athena, Cooper A. Voigt, Mengkun Tian, Anjan Goswami, Emily Toph, Moses Nnaji, Fanuel Mammo, Brent K. Wagner, Sungho Jeon, Wenshan Cai, Eric M. Vogel. 2025-10-04. A van der Waals material exhibiting room temperature broken inversion symmetry with ferroelectricity. https://arxiv.org/abs/2510.03977

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