Giant piezoresistivity in a van der Waals material induced by intralayer atomic motions

The presence of the van der Waals (vdW) gap in layered materials creates a wealth of intriguing phenomena different to their counterparts in conventional materials. For example, pressurization can generate a large anisotropic lattice shrinkage along the vdW stacking orientation and/or a significant interlayer sliding, and many of the exotic pressure-dependent properties derive from these mechanisms. Here we report a giant piezoresistivity in pressurized \(\beta \text{’}\)-In2Se3. Upon compression, a six-orders-of-magnitude drop of electrical resistivity is obtained below 1.2 GPa in \(\beta \text{’}\)-In2Se3 flakes, yielding a giant piezoresistive gauge \({\pi }_{P}\) of -5.33 GPa− 1. Simultaneously, the sample undergoes a semiconductor-to-semimetal transition without a structural phase transition. Surprisingly, linear dichroism study and theoretical first principles modelling show that these phenomena arise not due to shrinkage or sliding at the vdW gap, but rather are dominated by the layer-dependent atomic motions inside the quintuple layer, mainly from the shifting of middle Se atoms to their high-symmetric location. Our work not only provides a prominent piezoresistive material but also points out the importance of intralayer atomic motions beyond vdW gap.