Researchers at the National University of Singapore have shown that Landau levels in different valleys of a two-dimensional (2D), valleytronic material, monolayertungsten diselenide, (WSe2) can be aligned at critical magnetic fields.

In many areas of engineering and science, the goal is to align distinct entities such as two laser beams or two pillars. The alignment of quantized electronic layers can allow for the creation of pseudo-spinors, which are useful in quantum computing applications.

When a magnetic field is applied on a 2D material, quantized electronic levels are created. These levels are known as Landau levels. These levels are particularly relevant for valleytronic materials. Valleytronic materials allow one to control the spin and charge of electrons as well as the “valley” where they are located. In general, charge carriers in different valleys travel in opposite directions.

The research team headed by Associate Professor Quek Su Ying, Department of Physics, National University of Singapore, developed a method to account for dynamic electron-electron interactions in predicting valleytronic material energy levels in the presence of a magnet field. These many-body interactions amplify the magnetic field’s effects on materials, causing an increase in energy levels. The computational results for monolayer WSe2 were in quantitative agreement with experimental literature. This validates the new approach. This is achieved by amplification of the Lande g factors.

The team discovered that the increase in the g factor was due to a shift in the population density of charge carriers within each valley. This change is caused by a magnetic field change. The g-factors will drop abruptly if the magnetic field is strong enough to ensure that all carriers are in the same valley (all the carriers move to the blue Valley in the above image). The charge carriers can oscillate between the valleys at this critical magnetic field. This can cause the alignment of Landau levels within the valleys.

Dr. XuanFengyuan, a postdoctoral researcher on the research team, stated that “Due to large g-factors in WSe2, critical magnetic fields predicted are very small so this effect is possible in standard laboratories.”

“This work predicts Landau levels that are more stable to fluctuations in carrier density than previous proposals. Recent observations of fractional quantum Hall state in 2DWSe2 suggests the possibility of using Landau-level alignment to enable topological quant computing applications,” said Prof Quek.