DQMP Forum - Evidence of Weakly Dispersive Band in Twisted Bilayer Graphene from Nano-ARPES - Design of van der Waals Interfaces for Broad-Spectrum Optoelectronics

21.04.2020 13:00 – 14:30

Evidence of Weakly Dispersive Band in Twisted Bilayer Graphene from Nano-ARPES
Simone Lisi (Group of Prof. Baumberger)

Transport experiments in twisted bilayer graphene (TBG) revealed multiple superconducting domes separated by correlated insulating states1. These properties are generally associated with strongly correlated states in a flat mini-band of the hexagonal moir´e superlattice as it was predicted by band
structure calculations2.
We combined different imaging techniques and angle resolved photoemission with real and momentum space resolution (nano-ARPES) to map the band dispersion in TBG devices near charge neutrality. We observed large areas with homogeneous twist angle that support a flat band with spectral weight highly localized in momentum space3. The flat band is separated from the dispersive Dirac bands which show multiple moir´e hybridization gaps. These data establish the salient features of the TBG band structure, so far deduced from transport measurements and theory.
1 Y. Cao, et al., Nature, 556, 43 (2018); Y. Cao, et al., Nature, 556, 80 (2018)
2 R. Bistritzer et al., Proc. Natl. Acad. Sci, 108, 12233(2011)
3 S. Lisi et al., arxiv:2002.02289 (2020)


Design of van der Waals Interfaces for Broad-Spectrum Optoelectronics
Nicolas Ubrig (Group of Prof. Morpurgo)

Van der Waals interfaces based on two dimensional materials are promising for optoelectronics, as interlayer transitions between different compounds allow tailoring the spectral response over a broad range. However, issues such as lattice mismatch or a small misalignment of the constituent layers can drastically suppress electron-photon coupling for these interlayer transitions. Here, we engineer type-II interfaces by assembling atomically thin crystals that have the bottom of the conduction band and the top of the valence band at the Γ-point, thus avoiding any momentum mismatch. We find that these vdW interfaces exhibit radiative optical transitions irrespective of lattice constant, rotational/translational alignment of the two layers, or whether the constituent materials are direct or indirect gap semiconductors. Being robust and of general validity, our results broaden the scope of future optoelectronics device applications based on two-dimensional materials.

Lieu

Zoom Meeting

Zoom, Meeting ID: 582 067 708
https://unige.zoom.us/j/582067708

entrée libre