Valley-dependent spin polarization in bulk MoS2 with broken inversion symmetry

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Electron spin and valley degrees of freedom are key for information processing in materials like graphene and transition-metal dichalcogenides.
• Monolayer transition-metal dichalcogenides exhibit unique spin-valley coupling due to spin-orbit interaction.
• Understanding and controlling these degrees of freedom is crucial for next-generation electronic devices.

Purpose of the Study:

• To directly observe valley-dependent out-of-plane spin polarization in molybdenum disulfide (MoS2).
• To investigate the role of crystal structure, specifically non-centrosymmetric polytypes, in spin-valley phenomena.
• To explore the potential of these materials for spintronic applications.

Main Methods:

• Utilized spin- and angle-resolved photoemission spectroscopy (SARP) for direct observation of spin polarization.
• Employed a 3R polytype crystal of MoS2, which possesses a non-centrosymmetric structure.
• Confirmed valley polarization using circularly polarized photoluminescence spectroscopy.

Main Results:

• Directly observed valley-dependent out-of-plane spin polarization in MoS2.
• Results showed good agreement with first-principles theoretical predictions.
• Confirmed robust valley polarization in the 3R polytype MoS2 crystal.

Conclusions:

• The non-centrosymmetric 3R polytype of MoS2 enables the observation of spin polarization linked to electron valley.
• This discovery provides a foundation for developing devices that manipulate spin and valley degrees of freedom.
• Non-centrosymmetric transition-metal dichalcogenides are promising for future magnetic and electric control of spin/valley properties.