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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.

Layer-structured materials with van der Waals gaps have long been utilized as active electrode materials in rechargeable Li ion batteries. However, the intrinsic electrical, optical, and structural properties are not well understood at a single flake scale. We developed a planar nano battery for in situ measurement of large-area, uniform, two-dimensional (2D) flakes during lithiation process. A huge, simultaneous increase of optical transmittance and conductivity was observed with Lithium insertion in graphene and MoS2 flakes. The excellent performance (up to 200% transmittance increase and two orders magnitude of resistance decrease) is studied and explained by the unique band structure of the 2D materials and in situ TEM measurements. The proposed methodology can be applied to study a broad range of nanomaterials electrodes by electrochemical intercalation, and the excellent property of lithiated 2D materials will inspire a variety of applications such as electrochromic devices and transparent electrodes.

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