Ferroelastic switching in Alpha-Phase few-layer SnSe monochalcogenides by mechanical forces

Redhwan Moqbel^1*, Ranganayakulu K. Vankayala¹, Rajesh Kumar Ulaganathan¹, Raman Sankar¹, Min-Nan Ou¹, Chi-Cheng Lee², Kung-Hsuan Lin¹

¹Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
²Department of Physics, Tamkang University, Tamsui, New Taipei 251301, Taiwan

* Presenter:Redhwan Moqbel, email:redhwanmoqbel@gate.sinica.edu.tw

Monolayers belonging to the Group-IV monochalcogenide family are theoretically expected to display multiferroic behavior, simultaneously exhibiting ferroelectric and ferroelastic properties. In this work, we provide the first experimental confirmation of ferroelasticity in Group-IV monochalcogenides. Our study shows that few-layer SnSe with antiferroelectric stacking (α-SnSe) demonstrates multiferroic properties when the number of layers is odd, as verified through both experimental observations and theoretical simulations. The in-plane polarization direction of a five-layer α-SnSe flake is identified using polarization-resolved second harmonic generation (SHG) anisotropy measurements. Furthermore, we find that applying mechanical stress triggers ferroelastic switching in SnSe, producing a 90° rotation of the polarization, as validated by SHG results. Finally, first-principles calculations are employed to investigate the strain-dependent SHG response of α-SnSe few layers and to clarify the ferroelastic switching pathway.

Keywords: SHG, ferroelectric SnSe Few Layers, strain-dependent, Ferroelastic Switching