Photocurrent Spectroscopy of Correlated Insulator States in Rhombohedral Pentalayer Graphene

Rhombohedral multilayer graphene (RMG) has emerged as a crucial platform for studying quantum phenomena such as superconductivity and quantum anomalous Hall effects. Prior DC transport measurements revealed unexpected correlated insulating states at zero displacement field and zero charge density in rhombohedral pentalayer graphene (R5G), calling for further spectroscopic exploration. Utilizing Fourier-Transformed Infrared (FTIR) photocurrent spectroscopy, we have measured spectra at not only band insulator states but also correlated insulating states.

Firstly, I will present representative spectra of both band insulator and correlated insulator states in R5G. I will then demonstrate how these spectra evolve with the displacement field, revealing changes in the band structure. These observations help us identify spectroscopic signatures of electron correlation, thereby extending our understanding beyond conventional DC transport measurements. Finally, I will discuss the temperature dependence of these correlated gaps. Insights from this research deepen our understanding of RMG and offer valuable information for theoretical modeling.