Signatures of electric field and layer separation effects on the spin-valley physics of MoSe${}_2$/WSe${}_2$ heterobilayers: from energy bands to dipolar excitons

Abstract

We investigate the spin-valley physics (SVP) in MoSe${}_2$/WSe${}_2$ heterobilayers under external electric field (EF) and changes of the interlayer distance (ID). We analyze the spin ($S_z$) and orbital ($L_z$) degrees of freedom, and the symmetry properties of relevant band edges (at K, Q, and $\Gamma$ points) in high-symmetry stackings at 0 (R-type) and 60 (H-type) degree angles, the important building blocks of moiré or atomically reconstructed structures. We reveal distinct hybridization signatures of $S_z$ and $L_z$ in low-energy bands due to the wave function mixing between the layers, which are stacking-dependent and can be further modified by EF and ID. The H-type stackings favor large changes in the g-factors under EF, e. g. from $-5$ to $3$ in the valence bands of the H${}_h^h$ stacking, due to the opposite orientation of $S_z$ and $L_z$ in the individual monolayers. For the low-energy dipolar excitons (DEs), direct and indirect in $k$-space, we quantify the electric dipole moments and polarizabilities, reflecting the layer delocalization of the constituent bands. We found that direct DEs carry a robust valley Zeeman effect nearly independent of the EF but tunable by the ID, which can be experimentally accessible via applied external pressure. For the momentum-indirect DEs, our symmetry analysis indicates that phonon-mediated optical processes can easily take place. For the indirect DEs with conduction bands at the Q point for H-type stackings, we found marked variations of the valley Zeeman ($\sim 4$) as a function of the EF that notably stand out from the other DE species. Stronger signatures of the coupled SVP are favored in H-type stackings, which can be experimentally investigated in $\sim 60^{\text{o}}$ samples. Our study provides fundamental insights into the SVP of van der Waals heterostructures, relevant to understand the valley Zeeman of DEs and intralayer excitons.

19 pages, 15 figures, 8 tables

References in corpus (15)

• The Valley Hall Effect in MoS2 Transistors
• Observation of Long-Lived Interlayer Excitons in Monolayer MoSe2-WSe2 Heterostructures
• k.p theory for two-dimensional transition metal dichalcogenide semiconductors
• Resonantly hybridised excitons in moiré superlattices in van der Waals heterostructures
• Moiré excitons: from programmable quantum emitter arrays to spin-orbit coupled artificial lattices
• Van der Waals heterostructures for spintronics and opto-spintronics
• Theory of optical absorption by interlayer excitons in transition metal dichalcogenide heterobilayers
• Opto-Valleytronic Spin Injection in Monolayer MoS2/Few-Layer Graphene Hybrid Spin Valves
• Giant Valley-Zeeman Splitting from Spin-Singlet and Spin-Triplet Interlayer Excitons in WSe2/MoSe2 Heterostructure
• Optospintronics in graphene via proximity coupling
• Excitonic complexes in $n$-doped WS${}_2$ monolayer
• Spin-orbit coupling and spin relaxation in phosphorene: Intrinsic versus extrinsic effects
• Low-frequency Raman scattering in WSe${}_2$-MoSe${}_2$ heterobilayers: Evidence for atomic reconstruction
• Symmetry and Control of Spin-Scattering Processes in Two-Dimensional Transition Metal Dichalcogenides
• Direct STM Measurements of R- and H-type Twisted MoSe2/WSe2 Heterostructures

Cited by in corpus (1)

• Hybrid moiré excitons and trions in twisted MoTe${}_2$-MoSe${}_2$ heterobilayers