Excitons in mesoscopically reconstructed moiré heterostructures

Abstract

Contributions:A. H. conceived and supervised the project. X. H. and J. G. fabricated heterobilayer samples from native crystals by exfoliation-stacking. Z. Li. and I. B. synthesized monolayers and fabricated heterobilayer samples from CVD-grown crystals. K. W. and T. T. provided highquality hBN crystals. S. Z., Z. Li. and J. G. performed optical spectroscopy. A. R. performed scanning electron microscopy imaging. A. S. B. developed the theoretical model and together with I. A. V. performed numerical calculations. S. Yu. K. carried out DFT calculations.

Signatures of Electric Field and Layer Separation Effects on the Spin-Valley Physics of MoSe2/WSe2 Heterobilayers: From Energy Bands to Dipolar Excitons

“…We focus on artificially stacked MoSe /WSe heterostructures with relative angles of 0° (R-type) and 60° (H-type). When the individual MoSe and WSe layers are stacked together, the angle is not precisely 0° or 60°, and the small misalignment can give rise to moiré superlattices or atomic reconstruction [ 19 , 20 , 52 , 53 , 54 , 55 , 56 , 57 ], with length scales of tens of nm. However, either in the moiré or in the atomic reconstruction perspective, there are distinct contributions from well-defined high-symmetry stackings that dominate the observed properties [ 20 , 64 , 68 , 69 , 70 ], such as the dipolar excitons selection rules and g-factors.…”

“…In this section, we explore the spin and orbital degrees of freedom for the relevant band edges (indicated in Figure 1 g) at zero electric field and at the equilibrium interlayer distance. We follow recent first-principles developments, to compute the orbital angular momenta in monolayer TMDCs [ 64 , 65 , 66 , 67 ], which has also been successfully applied to investigate a variety of more complex TMDC-based systems and van der Waals heterostructures [ 27 , 53 , 57 , 80 , 85 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 ]. We do not aim to provide a detailed description of the methodology here, but briefly summarize the main points.…”

“…These MoSe /WSe heterostructures were investigated in Refs. [ 53 , 57 , 64 , 67 , 80 ] but here we extend our analysis to incorporate more bands, and later investigate the dependence of electric field and interlayer distance. We emphasize here that the electronic and spin properties calculated with the DFT also provide a reliable benchmark for further studies, as WIEN2k [ 81 ] is one of the most accurate DFT codes available [ 100 ], and is particularly suitable for studying the spin-physics of 2D materials and van der Waals heterostructures [ 23 , 24 , 27 , 95 , 101 , 102 , 103 , 104 , 105 ].…”

“…Interestingly, dipolar excitons exhibit long recombination times [ 39 , 40 , 41 ], robust out-of-plane electric dipole moments [ 42 , 43 , 44 , 45 , 46 ], and giant valley Zeeman signatures that are dependent on the twist angle and atomic registry [ 20 , 43 , 47 , 48 , 49 , 50 , 51 ]: these are attractive features that could be exploited in exciton-based opto-spintronics devices [ 17 , 18 ], such as dipolar excitons quantum emitters [ 43 ] and diode transistors [ 46 ]. Furthermore, these MoSe /WSe are suitable platforms on which to study the optical signatures of moiré superlattices [ 19 , 20 , 52 , 53 ] and atomic reconstruction [ 54 , 55 , 56 , 57 ]. From a fundamental perspective, there is still some debate about the energy bands that constitute these dipolar excitons.…”

Coulomb-correlated states of moiré excitons and elementary charges on a semiconductor moiré lattice at integer and fractional fillings

“…Akin to WSe 2 /WS 2 heterostacks, MoSe 2 /WS 2 HBLs feature relatively large lattice incommensurability of 4%, which inhibits nanoscale and mesoscopic reconstruction ubiquitous in systems with small lattice mismatch as in MoS 2 /WS 2 or MoSe 2 /WSe 2 [32][33][34][35][36][37]. Sizable lattice mismatch stabilizes moiré phenomena by lock HBLs rigidly in the canonical moiré geometry illustrated in Fig.…”