Supporting Information. Valley Zeeman Splitting and Valley Polarization of Neutral and Charged Excitons in Monolayer MoTe2 at High Magnetic Fields

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1 Supporting Information Valley Zeeman Splitting and Valley Polarization of Neutral and Charged Excitons in Monolayer MoTe2 at High Magnetic Fields Ashish Arora,*, Robert Schmidt, Robert Schneider, Maciej R. Molas, Ivan Breslavetz, Marek Potemski, and Rudolf Bratschitsch*, Institute of Physics and Center for Nanotechnology, University of Münster, Wilhelm-KlemmStrasse 10, Münster, Germany Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 rue des Martyrs, Grenoble, France Corresponding Authors: * (RB) * (AA) *Fax: Atomic force microscopy, Raman spectroscopy, spectroscopy of monolayer and few-layer MoTe2 flakes and photoluminescence Figure S1: Optical microscope image and AFM profile of (a) the 1L MoTe2 flake on Si/SiO2 substrate and (b) a 2L and a 3L thick MoTe2 flake on Si/SiO2 substrate. (c) Raman spectra of 1L, 2L, and 3L thick MoTe2 flakes on sapphire and (d) on Si/SiO2 substrate. Figures S1 (a) and (b) show optical microscopy images of monolayer (1L), 2L, and 3L-MoTe2 flakes on Si/SiO2(80 nm) substrate. The monolayer thickness is 0.65 ± 0.08 nm. This value is determined by measuring the step height between a 2L and a 3L flake with an atomic force microscope (AFM) (Fig. S1 (b)), and is in agreement with a previous report.1 The 1L-height of S1

2 the MoTe 2 flake measured with the AFM directly from substrate to monolayer is 1.6±0.1 nm, and larger than the theoretical value. This is due to contamination between the monolayer and the substrate, as observed earlier for MoS 2, 2 MoSe 2, 3 WS 2, 4 and WSe 2. 5 However, the monolayer is unambiguously identified by Raman spectroscopy (see below). For performing Raman spectroscopy measurements 600 μw of a 632 nm laser is focused to a diameter of ~ 1 μm. Raman spectra are obtained for 1L, 2L and 3L MoTe 2 flakes, placed on Si/SiO 2 or sapphire substrates (Fig S1 (c) and (d)). The Raman active modes A and E are identified in all flakes. 1,6 8 In 2L and 3L flakes, the B mode is observed in addition, which is absent in the 1L flake. In that way, the monolayer is unambiguously identified. 1,6 8 The A mode splits into two lines for the 3L flake, which lets one distinguish the 2L and 3L flakes. 1,6 8 Figure S2 shows microphotoluminescence (μpl) spectra for 1L MoTe 2 at temperatures ranging from T = 4 K to 220 K. A continuous-wave 514 nm laser is used as an excitation source with a power of 20 μw focused on the sample (focus diameter ~ 1 μm). Raising the temperature above 220 K does not yield any measurable PL emission. The charged exciton emission is discernible below 100 K. At higher temperatures the PL is dominated by the neutral exciton emission. This behavior is in qualitative agreement with a previous report on ML MoTe 2, 6 as well as other ML transition metal dichalcogenides Figure S2: Microphotoluminescence spectra of ML MoTe 2 on Si/SiO 2 substrate, as a function of temperature T = 4 K K, in steps of 20 K. PL corresponding to the neutral X and charged X ± excitons is observed. The spectra are shifted vertically in steps of 200 counts μw -1 s -1 for clarity, and have been multiplied by the factors noted on the right side of the respective curve. S2

3 Summary of excitonic g-factors in monolayer transition metal dichalcogenides Table 1: Experimentally obtained g-factors for the neutral ( and ) and charged ( ± ) excitons for various monolayer TMDCs including the present work along with the corresponding references. Material (monolayer) "! ± " # 4.0± ± MoS 2 4.6± ± WS ± ± MoSe 2 WSe 2 4.1± ±0.2 17,18 4.4± to ± ± ± ± ± ± ± ± MoTe 2 (present work) 4.6± ± ±0.6 S3

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