2020 Fiscal Year Annual Research Report
Two Dimensional Magnetic Material: Spintronics & Valleytronics Applications
| Project/Area Number |
19K15381
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| Research Institution | National Institutes for Quantum and Radiological Science and Technology |
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Principal Investigator |
Hashmi Arqum 国立研究開発法人量子科学技術研究開発機構, 関西光科学研究所 光量子科学研究部, 博士研究員(任常) (90815325)
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| Project Period (FY) |
2019-04-01 – 2021-03-31
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| Keywords | Magnetic 2D material / DFT / Spintronics / Valleytronics / Spin-valley Hall |
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| Outline of Annual Research Achievements |
Regarding the work on valleytronics, using first-principles calculations, I investigated the possibility of realizing valley Hall effects (VHE) in the blistered graphene sheet. The blister structures are composed of pentagonal and heptagonal rings of carbon atoms, which show a strong tendency toward out-of-plane deformation with increasing blister size. The geometric distortion leads to Van Hove singularities (VHS) which could induce exchange splitting in otherwise paramagnetic graphene. Unlike the ribbon edges, these atomic-scale blisters are fully immersed within the graphene sheet, hence, its magnetic state is protected from contamination and reconstruction effects that could hamper experimental detection.
It showed that the VHS induced by structural deformations can give rise to interesting spin-valley Hall phenomena. The broken degeneracy of spin degree of freedom results in spin-filtered QVH states, and the valley conductivity has a Hall plateau of ±e^2/2h. While the blistered structures with time-reversal symmetry show the QVHE with the opposite sign of σ_xy^(K/K') (e^2/(h)) in the two valleys.
Remarkably, these results show that a distinguishable chiral valley pseudospin state can occur even in the presence of VHS-induced spin splitting. The robust chiral spin-momentum textures in both massless and massive Dirac cones of the blistered systems indicate significant suppression of carrier back-scattering.
This study provided a new approach to realize spin-filtered and spin-valley contrasting Hall effects in next-generation quantum devices without any external field.
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