Tailoring excitonic states of van der Waals bilayers through stacking configuration, band alignment, and valley spin

Abstract

Excitons in monolayer semiconductors have large optical transition dipole for strong coupling with light field. Interlayer excitons in heterobilayers, with layer separation of electron and hole components, feature large electric dipole that enables strong coupling with electric field and exciton-exciton interaction, at the cost that the optical dipole is substantially quenched (by several orders of magnitude). In this letter, we demonstrate the ability to create a new class of excitons in transition metal dichalcogenide (TMD) heteroand homo-bilayers that combines the advantages of monolayer-and interlayer-excitons, i.e. featuring both large optical dipole and large electric dipole. These excitons consist of an

Twist-angle dependence of moiré excitons in WS2/MoSe2 heterobilayers

“…These results are consistent with the spin selection rules of the excitonic transitions illustrated in Fig. 1 b 25 . Assuming the interlayer exciton-binding energy is about the same in R- and H-stacking bilayers 26 , and the difference δ R − δ H is comparable to the spin–orbit splitting of WS 2 conduction band (Fig.…”

“…To analyze the results quantitatively, we first obtain the energies, E LHX and E UHX , and oscillator strengths of the hybrid states by fitting the RC spectra using the transfer matrix method, where the hybrid excitons are modeled as Lorentz oscillators (see "Methods", Supplementary Fig. 3 and Note 5) 25,27 . The fitted spectrum agrees well with the data, as shown in Fig.…”

Twist-tailoring Coulomb correlations in van der Waals homobilayers

“…Hybridization effects between the electronic states of the constituent layers allow the band structure to be externally controlled by the twist angle θ (refs. 13,[15][16][17][18][19][20].…”

Formation and tuning of moiré excitons in large-twist angle WS2/MoSe2 heterobilayers

“…1c, in the R-stacking bilayers (θ = 2. To analyze the results quantitatively, we first obtain the energies, E LHX and E U HX , and oscillator strengths of the hybrid states by fitting the RC spectra using the transfer matrix method, where the hybrid excitons are modeled as Lorentz oscillators (See Supplemental Material Fig.S3) [24,25].…”