Spin-Valley Physics of TMDs Under Strain Explored: nanomaterials nanoanalysis spintronics TMDs NJPhysics
By Bhavna KavetiAug 15 2022Reviewed by Susha Cheriyedath, M.Sc. Transition metal dichalcogenides are useful in investigating the manifestations of spin-valley physics under the external stimulus. A study published in the New Journal of Physics explored the effect of strain on orbital angular momenta, Berry curvatures, and effective g-factors via the ab initio method.
One percent variation in strain modified the bright exciton’s g-factors by approximately 0.3 and 0.2 for tungsten and molybdenum , and for dark exciton’s g-factors, it was approximately 0.5 and 0.3 for W and Mo, respectively. Conducting magneto-optical experiments helped visualize these predictions in the strained sample at low temperatures. The calculations suggested that the strain effect was a possible cause of g-factor fluctuations.
The lack of crystal lattice’s inversion symmetry and the presence of heavy metal elements mark strong SOC physics at K-valleys via spin polarization in the out-of-plane direction. Thus, the spin-valley locking of holes and electrons allows selective excitation of exciton quasi-particles wither from K or -K valley.
In addition to spin-valley physics, transition metal dichalcogenides are suitable materials for straintronics. Applying controllable strain on them can adjust the exciton’s optical emission energy by several hundreds of millielectronvolts. Additionally, strain suppresses the nonradiative exciton recombination, preserving the photoluminescence’s quantum yield close to unity.
K-valley under compressive strain showed an unexpected spin-mixing regime for the conduction band with spin-down electrons. The direct excitons originating from K-valley’s low energy bands revealed two trends in the Zeeman effect. Conclusion To conclude, transition metal dichalcogenides were explored to study their spin-valley physics under biaxial strain. Several transition metal dichalcogenides with hexagonal crystal structures were used to analyze orbital angular momenta, spin-mixing, g-factors, and Berry curvatures. The results revealed compressive strain-dependent spin-mixing features at the K-valleys.
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