Physicists from Australia, Russia, and the UK have created an artificial two-dimensional electrostatic crystal whose properties can be continuously changed using electric voltage and a magnetic field. The international research group formed it within a semiconductor structure based on gallium arsenide and aluminum-gallium arsenide, creating a periodic electrostatic landscape in a thin electron layer.
In the same chip, scientists were able to reconfigure the electronic spectrum from "graphene-like" to "kagome-like," obtaining different types of energy bands without replacing the sample. The work, involving employees of the Institute of Semiconductor Physics SB RAS, was published in Nature Physics.
The main difference of the created system is the ability to control the artificial crystal directly during the experiment. For this, the researchers used two gates: one regulates the electron concentration, the other — the depth of the periodic potential.
Electric lattice instead of atomic
In a conventional crystal, electrons move along a lattice formed by the material's atoms. Here, scientists created a similar lattice artificially — using an electric field. To do this, a metal gate with triangularly arranged holes every 100 nanometers was placed above the two-dimensional electron layer. Electric voltage creates peculiar "wells" and "hills" for electrons around them, and a second, solid gate allows changing the strength of this landscape. At the same time, there are no specially added impurities in the semiconductor that could create random interference.
Thanks to this, the researchers obtained a clean and controllable system in which they can switch between a mode where electron behavior is primarily determined by the artificial lattice, and a mode where interactions between the electrons themselves begin to play a major role.
The samples were made and studied at the University of New South Wales, and the initial GaAs/AlGaAs multilayer structures were provided by the Cavendish Laboratory of Cambridge University. Employees of the A.V. Rzhanov Institute of Semiconductor Physics SB RAS, Olga and Vitaly Tkachenko, supported the experiment with calculations and optimized the design of the semiconductor structure, and also investigated transport over a wide range of electron concentrations and magnetic fields.
According to Vitaly Tkachenko, the path from the initial idea and calculations to a working device took many years.