Multiple-peak resonance of optical second harmonic generation arising from band nesting in monolayer transition metal dichalcogenides TX2 on SiO2/Si

Dispersion of the nonlinear susceptibility of MoS2 and WS2 from second-harmonic scattering spectroscopy

“…S2, the relative measures found for WS 2 samples w2 and w3 are very similar; only a slightly higher resonance at 830 nm is observed for sample w3 with the highest proportion of monolayers. The absence of any wavelength shift [19] is to be mentioned, suggesting that the SH response within suspensions mainly originates from monolayers. However, we cannot exclude a contribution of the flake edges to the measured composite χ (2) susceptibility for these nanosheets with low lateral dimensions.…”

“…The first study by Malard et al [3] showed a significant amplification of the SHG around the C exciton within MoS 2 layers. Several reports have since confirmed that an enhancement occurs around the three main UV-visible excitonic transitions, typically denoted as A, B, and C [6,18,19]. One can also expect that quantitative dispersion measurements will lead to a better understanding of the nonlinear optical properties of TDMs through comparison with theoretical models [20,21].…”

Doubly‐Resonant Enhancement of Second Harmonic Generation from a WS2 Nanomesh Polymorph with a Modified Energy Landscape

“…In most TMDs, the C feature is broadband (≈10 times broader than the A and B). [ 22 ] Rather than arising from a single optical transition, the C spectral feature is associated with multiple transitions from a ring of points between the Λ and Γ points of the Brillouin zone [ 57 ] and it is attributed to “band nesting.” [ 59 ] The band nesting condition is that eV/(2πa) (where 2π/a is the modulus of the reciprocal lattice vector) with , where E c and E v are the conduction band and valence band energies, respectively. The band nesting condition implies that, in its energy region, the conduction and valence bands are parallel (see schematic in Figure 1a).…”

“…In most TMDs, the C feature is broadband (≈10 times broader than the A and B). [22] Rather than arising from a single optical transition, the C spectral feature is associated with multiple transitions from a ring of points between the Λ and Γ points of the Brillouin zone [57] and it is attributed to "band nesting." [59] The band nesting condition is that…”

“…[18] As a result, TMD materials exhibit highly tunable, thickness-dependent linear and nonlinear optical properties. [19] SHG studies of TMD flakes/sheets (monolayers and van der Waals bonded multilayers of typically 1-10 layers) have been reported for WS 2 , [20][21][22] WSe 2 , [23][24][25][26] MoS 2 , [27][28][29][30][31][32][33] MoSe 2 , [34] MoTe 2 , [35] as well as for MoS 2 -WS 2 and MoS 2 -WSe 2 heterostructures. [36] Huge SHG responses were reported [19] (≈10 3 times more than in BBO and KTP, [37] and ≈10 5 more than in bulk TMDs).…”