Tunneling between twisted sheets of bilayer graphene: a new method for controlling current?

The basic way to control the current through a transistor is to change the concentration of charge carriers — that is, electrons. But quantum particles are weird: Unlike a ball bouncing back after it hits a wall, an electron can transport through an energy or material barrier in a process known as tunneling.

By tapping into these tunneling effects, Sokolik et al. demonstrated a new method to control currents in nanoelectronic devices. The researchers varied the voltage applied to gate electrodes attached to twisted bilayer graphene, shifting the associated Fermi levels — the amount of work needed to move an electron from one layer to the other — and altering the tunneling current.

“This is a different method to control the current — not by simply changing concentrations, but by using more complicated quantum mechanical effects,” said author Alexey Sokolik.

For this to work, two sheets of bilayer graphene must be twisted with respect to each other, with an occupied electron state in one, and an unoccupied electron state in the other. As the relative twist between the two materials increases, the electrons tunneling between the layers experience a larger change in relative momentum, but they maintain their energy from the Fermi level of the first material to the Fermi level of the second. This is a delicate balance; too large a twist can lead to too large a charge carrier imbalance between the layers, preventing good tunneling. Tunneling, in effect, controls the electric current.

With further manipulations of the twist and applied voltage, the researchers hope these findings can be used in high-sensitivity nanoscale devices.

Source: “Probing the features of electron dispersion by tunneling between slightly twisted bilayer graphene sheets,” by Alexey A. Sokolik, Azat F. Aminov, Evgenii E. Vdovin, Yurii N. Khanin, Mikhail A. Kashchenko, Denis A. Bandurin, Davit A. Ghazaryan, Sergey V. Morozov, and Kostya S. Novoselov, Applied Physics Letters (2025). The article can be accessed at https://doi.org/10.1063/5.0303858 .