[1] [1] Novoselov K S, Geim A K, Morozov S V, et al. Two-dimensional gas of massless dirac fermions in grapheme[J]. Nature, 2005, 438: 197-200.

[2] [2] Xia F, Farmer D B, Lin Y, et al. Graphene field-effect transistors with high on/off current ratio and large transport band gap at room temperature[J]. Nano Letters, 2010, 10: 715-718.

[3] [3] Zhuang H L, Hennig R G. Computational search for single-layer transition-metal dichalcogenide photocatalysts[J].Journal of Physical Chemistry C, 2013, 117: 20440-20445.

[4] [4] Kang J, Tongay S, Zhou J, et al. Band offsets and hetero-structures of two-dimensional semiconductors[J]. Applied Physics Letters, 2013, 102: 12111.

[5] [5] Zhu B, Zeng H, Dai J, et al. Anomalously robust valley polarization and valley coherence in bilayer WS2[J]. PNAS, 2014, 111: 11606-11611.

[6] [6] Schaibley JR, Yu H, Clark G, et al. Valleytronics in 2D materials[J]. Nat Rev Mater, 2016, 1: 16055.

[7] [7] SU Hui-min, WEI Cheng-rong, DENG Ai-ying, et al. Anomalous enhancement of valley polarization in multilayer WS2 at room temperature[J]. Nanoscale, 2017, 9: 5148-5154.

[8] [8] Ramasubramaniam A. Large excitonic effects in monolayers of molybdenum and tungsten dichalcogenides[J]. Phys Rev B, 2012, 86: 115409.

[9] [9] Dyakonov MI, Perel VI. Spin orientation of electrons associated with inter-band absorption of light in semiconductors[J]. Exp Theor Phys, 1971, 33: 1053.

[10] [10] Yafet Y. Calculation of the g factor of metallic sodium[J]. Phys Rev, 1952, 85: 478-478.

[11] [11] Jin C, Kim J, Mib U, et al. Imaging of pure spin-valley diffusion current in WS2-WSe2 heterostructures[J]. Science, 2018, 360: 893.

[12] [12] Munoz L, Perez E, Bellani V, et al. Exciton dynamics and spin relaxation in unstrained and tensile-strained quantum wells[J]. Journal of the Optical Society of America B, 1996, 13.

[13] [13] Yuhei M, Satoru K, Feijiu W, et al. Evidence for line width and carrier screening effects on excitonic valley relaxation in 2D semiconductors[J]. Nat Commun, 2018, 9: 2598.

[14] [14] WANG Yan-long, CONG Chun-xiao, SHANG Jing-zhi, et al. Unveiling exceptionally robust valley contrast in AA- and AB-stacked bilayer WS2[J]. Nanoscale Horiz, 2019, 4: 396-403.

[15] [15] Jin C, Regan E C, Yan A, et al. Observation of moire excitons in WSe2/WS2 hetero-structure super-lattices[J]. Nature, 2019, 567: 76-80.

[16] [16] Yu H, Liu G B, Tang J, et al. Moiré excitons: from programmable quantum emitter arrays to spin-orbit-coupled artificial lattices[J]. Science Advances, 2017, 3: e1701696.

[17] [17] Tran K, Moody G, Wu F, et al. Evidence for moiré excitons in van der Waals heterostructures[J]. Nature, 2019, 567: 71-75.

[18] [18] Rivera P, Seyler KL, Yu H, et al. Valley-polarized exciton dynamics in a 2D semiconductor heterostructure[J]. Science, 2016, 351: 6174.

[19] [19] Hsu W T, Lu L S, Wu P H, et al. Negative circular polarization emissions from WSe2/MoSe2 commensurate heterobilayers[J]. Nat Commun, 2018, 9: 1356.