Isolation and Characterization of Few-Layer Manganese Thiophosphite

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1 Supporting Information for: Isolation and Characterization of Few-Layer Manganese Thiophosphite Gen Long 1, Ting Zhang 1,2, Xiangbin Cai 1, Jin Hu 3, Chang-woo Cho 1, Shuigang Xu 1,4, Junying Shen 1, Zefei Wu 1, Tianyi Han 1, Jiangxiazi Lin 1, Jingwei Wang 1, Yuan Cai 1, Rolf Lortz 1, Zhiqiang Mao 3,and Ning Wang 1,* Affiliations: 1. Department of Physics and Center for Quantum Materials, the Hong Kong University of Science and Technology, Hong Kong, China 2. Institute for Advanced Study, The Hong Kong University of Science and Technology, Hong Kong, China 3. Department of Physics and Engineering Physics, Tulane University, New Orleans, LA , USA 4. National Graphene Institute, University of Manchester, Manchester M13 9PL, UK *Correspondence to:

2 1. Elemental analysis of MnPS3 flake Fig.S1. Energy-dispersive X-ray spectroscopy (EDX) mapping of a MnPS3 flake. The Mapping results demonstrate an even distribution of the three elements. Table S1. Mass and atoms ratios of the MnPS3 flake extracted from the EDX results. Mass (%) Atoms (%) Mn P S

3 2. Anisotropic Raman peaks of 10 nm-thick MnPS3 flake. Fig. S2. Angle-resolved polarized Raman spectrum of 10 nm-thick MnPS3. The Raman peaks in 10 nm-thick MnPS3 flakes exhibit the same anisotropic behaviors with 4-layer ones shown in the main text.

4 3. The assignment of MnPS3 Raman modes and phonon frequencies Table S1 The assignment of Raman modes Raman shift Phonon frequency Raman susceptibility Determinant cm E cm -1 / / / cm E cm cm E-4 The Raman susceptibility calculations were performed with LDA framework, with Brillouin zone sampling mesh , energy cutoff 42 Ha, and norm-conserving pseudo-potential method, with ABINIT code 1-2. However such method gives poor accuracy in phonon frequencies, due to the poor description of electron correlation effect under standard LDA framework that dominating in Mn ions. Therefore we adapted LDA+U method together with projector augmented wave (PAW) technique to estimate the phonon frequencies, with the obtained Raman active phonon mode frequencies are now only ~4% lower than the experimental results (Unfortunately with ABINIT code LDA+U can t be used to calculate Raman susceptibility). Our calculation results are in consistence with the previous reported ones 3. Combine with these two methods the Raman active modes can be reliably assigned by symmetry of vibration eigenvectors.

5 Fig. S3 Eigen displacements of MnPS3 unit cell corresponding to phonon modes. (a) Frequency: cm -1. (b) Frequency: cm -1. (c) Frequency: cm -1. Here the eigenvectors are plotted within the primitive cell of MnPS3. 4. Transfer curves of MnPS3 Fig. S4. Transfer curves of MnPS3 crystals biased by LG with thickness ranging from 2 layers to 50 nm (around 60 layers). Extracted layer-dependent charge carrier mobilities are shown in the main text.

6 5. The instability of MnPS3 flakes Fig. S5 The instability of MnPS3 crystal. The optical image of a MnPS3 flake on a SiO2 substrate before and after annealing at 400 for 2 hours in argon atmosphere. The scale bar is 10 um. After annealing, the naked MnPS3 flakes are evaporated while those covered with hexagonal boron nitride (h-bn) are well protected. Supplementary references: 1. Gonze, X.; Jollet, F.; Araujo, F. A.; Adams, D.; Amadon, B.; Applencourt, T.; Audouze, C.; Beuken, J.-M.; Bieder, J.; Bokhanchuk, A., Recent Developments in the ABINIT Software Package. Comput. Phys. Commun. 2016, 205, Gonze, X., A Brief Introduction to the ABINIT Software Package. J. Metastable. Cryst. Mater. 2005, 220, Bernasconi, M.; Marra, G.; Benedek, G.; Miglio, L.; Jouanne, M.; Julien, C.; Scagliotti, M.; Balkanski, M., Lattice Dynamics of Layered MPX3 (M= Mn, Fe, Ni, Zn; X= S, Se) Compounds. Phys. Rev. B 1988, 38,