Graphitic Polytypes in Penta-Layer Graphene

Graphitic polytypes, with distinct meta-stable stacking arrangements of graphene layers, exhibit a diverse range of electro-optical properties. Polytypes with flat dispersions can show electronic correlations such as orbital magnetism, unconventional superconductivity, and anomalous fractional quantum Hall states at low temperatures. Recently, we reported the emergence of spontaneous electric polarization and its intriguing doping dependence at room temperature for mixed-stacked tetra-layer polytypes. These phenomena extend to multilayer graphitic polytypes. For instance, the commensurate stacking of five graphene layers can result in six different periodic crystal structures, each with unique symmetries and responses, particularly under infrared/low energy excitations. Among these, two polytypes are expected to exhibit spontaneous electric polarization due to broken inversion and mirror symmetry. However, identifying specific polytype crystals and their orientations remains challenging. We address this by reporting distinct Raman, second harmonic, and electric surface potential measurements for the six polytypes in penta-layers, enabling their deterministic identification. Additionally, we report the relative abundances and stability of the polytypes and their in-plane and out-of-plane polar responses. These advancements are a crucial step towards the development of multi-ferroic, "slidetronic" devices that rely on structural transitions between polytypes through interlayer van der Waals sliding.