Experimental demonstration of the suppression of optical phonon splitting in 2D materials by Raman spectroscopy

I Z acknowledges the Swiss National Science Foundation research grant (Project Grant No. 200021_165784). M D L acknowledges support from the Swiss National Science Foundation Ambizione grant (Grant No. PZ00P2_179801). R R acknowledges support from the Ministerio de Economia, Industria y Competitividad (MINECO) under grant FEDER-MAT2017-90024-P and the Severo Ochoa Centres of Excellence Program under grant SEV-2015-0496 and by the Generalitat de Catalunya under Grant Nos. 2017 SGR 1506. X C acknowledges financial support by the Ministerio de Economia, Industria y Competitividad under grant TEC2015-67462-C2-1-R (MINECO/FEDER), the Ministerio de Ciencia, Innovacion y Universidades under Grant No. RTI2018-097876-B-C21 (MCIU/AEI/FEDER, UE), and the EU Horizon2020 research and innovation program under Grant No. GrapheneCore2: 785219. C S and D I acknowledge support by the Swiss Nanoscience Institute (SNI), the ERC project TopSupra (787414), the European Union Horizon 2020 research and innovation program under grant agreement No. 785219 (Graphene Flagship), the Swiss National Science Foundation and the Swiss NCCR QSIT. J.M.-S. acknowledges support through a Clarin Marie Curie-COFUND grant from the Government of the Principality of Asturias and the EU (PA-18-ACB17-29), and the Ramon y Cajal Program (RYC2018-026196-I) from the Government of Spain. R T acknowledges support by European Union's Horizon 2020 research and innovation programme (SPQRel grant agreement no. 679183). K W and T T acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan and the CREST(JPMJCR15F3), JST.