Sliding-driven symmetry breaking induced ferroelectric polarization and phonon property modulation in a <b> <i>β</i> </b>-GaSe bilayer

Introducing ferroelectricity through symmetry breaking induces profound changes in the physical properties of a material. This study comprehensively tracks the ferroelectric polarization and phonon property changes resulting from interlayer sliding in a β-GaSe bilayer. The results indicate that sliding the upper layer of the bilayer induces charge transfer, causing polarization accompanied by periodic changes and reversal in non-polarized β-GaSe. Simultaneously, low-frequency optical phonons in polarized structures soften significantly, exhibiting a minimum or rapid decrease accompanied by the maximum value of in-plane polarization. Additionally, the sliding symmetry breaking has complex effects on phonon transport, causing intriguing changes in transport characteristics due to variations in group velocity and linewidth, which are closely related to ferroelectric polarization. This study reveals not only the polarization achieved in the β-GaSe bilayer through sliding-induced symmetry breaking but also its complex effects on phonons and profound physical changes, enriching our understanding of the associated condensed matter physics.