Infrared Spectroscopy for Diagnosing Superlattice Minibands in Magic-angle Twisted Bilayer Graphene (2404.05716v1)
Abstract: Twisted bilayer graphene (TBG) represents a highly tunable, strongly correlated electron system owed to its unique flat electronic bands. However, understanding the single-particle band structure alone has been challenging due to complex lattice reconstruction effects and a lack of spectroscopic measurements over a broad energy range. Here, we probe the band structure of TBG around the magic angle using infrared spectroscopy. Our measurements reveal spectral features originating from interband transitions whose energies are uniquely defined by the twist angle. By combining with quantum transport, we connect spectral features over a broad energy range (10 to 700 meV) spanning several superlattice minibands and track their evolution with twist angle. We compare our data with calculations of the band structures obtained via the continuum model and find good agreement only when considering a variation of interlayer/intralayer tunnelling parameters with the twist angle. Our analysis suggests that the magic angle also shifts due to lattice relaxation, and is better defined for a wide angular range from 0.9{\deg} to 1.1{\deg}. Our work provides spectroscopic insights into TBG's band structure and offers an optical fingerprint of the magic angle for screening heterostructures before nanofabrication.
- E. Y. Andrei and A. H. MacDonald, Graphene bilayers with a twist, Nature materials 19, 1265 (2020).
- J. L. Dos Santos, N. Peres, and A. C. Neto, Graphene bilayer with a twist: Electronic structure, Physical review letters 99, 256802 (2007).
- R. Bistritzer and A. H. MacDonald, Moiré bands in twisted double-layer graphene, Proceedings of the National Academy of Sciences 108, 12233 (2011).
- G. Tarnopolsky, A. J. Kruchkov, and A. Vishwanath, Origin of magic angles in twisted bilayer graphene, Physical review letters 122, 106405 (2019).
- P. Moon and M. Koshino, Optical absorption in twisted bilayer graphene, Physical Review B 87, 205404 (2013).
- H. Min and A. H. MacDonald, Origin of universal optical conductivity and optical stacking sequence identification in multilayer graphene, Physical Review Letters 103, 067402 (2009).
- T. Ando and M. Koshino, Optical absorption by interlayer density excitations in bilayer graphene, Journal of the Physical Society of Japan 78, 104716 (2009).
- N. N. Nam and M. Koshino, Lattice relaxation and energy band modulation in twisted bilayer graphene, Physical Review B 96, 075311 (2017).
- T. Cea, P. A. Pantaleón, and F. Guinea, Band structure of twisted bilayer graphene on hexagonal boron nitride, Physical Review B 102, 155136 (2020).
- P. Griffiths, J. De Haseth, and J. Winefordner, Fourier Transform Infrared Spectrometry (Wiley, 2007).