Electron transport in the presence of valley-orbit interaction

The progress of the silicon-based integrated circuit industry has been described by Moore’s law for more than half a century. But downscaling has appeared to reach its limit as various problems start to arise as devices reach the nano-scale. Now, researchers have turned to 2D materials with honeycomb lattices, like graphene, as an alternative solution to the more traditional silicon-based devices.

These materials have multiple valleys, or local minima, in the electronic band structure of the first Brillouin zone and possess a novel degree of freedom known as valley pseudospin in addition to charge and spin. The new article investigates electron transport in the presence of a valley-orbit interaction, which occurs when a valley pseudospin interacts with an electric field.

Using graphene-based quantum structures as an example, the researchers employed a full-zone tight-binding method to calculate the electronic band structure of the material, which included the valley degree of freedom.

They considered lateral quantum structures with multiple well/barrier interfaces using a platform of AB stacked bilayer graphene. For a single-barrier structure, they found that the valley-flipped transmission is negligible compared to the valley-conserved one, and the valley contrast in the transmission increases with increasing barrier width or height.

For a double-barrier structure, however, the valley-flipped transmission is enhanced at resonant tunneling, and the resonant energy levels are valley split, and the splitting increases with increasing asymmetry between the barriers.

Overall, the results demonstrate the valley dependence in electron transport in 2D material-based quantum structures. It also suggests the possibility of realizing valley-based electronics with such structures for applications in nano-electronics.

Source: “Valley aspect of lateral tunneling transport,” by Bing-Chen Huang, Feng-Wu Chen, Yen-Chun Chen, and G. Y. Wu, Journal of Applied Physics (2019). The article can be accessed at https://doi.org/10.1063/1.5085452 .