New technique to obtain individual fingerprint of the conducting edge states

A new technique makes it possible to obtain an individual fingerprint of the current-carrying edge states occurring in novel materials such as topological insulators or 2-D materials.

Measured tunneling current and its dependence on the two applied magnetic fields: The fans of red/yellow curves each correspond to a fingerprint of the conducting edge states. Each individual curve separately shows one of the edge states. Credit: University of Basel, Department of Physics
Measured tunneling current and its dependence on the two applied magnetic fields: The fans of red/yellow curves each correspond to a fingerprint of the conducting edge states. Each individual curve separately shows one of the edge states. Credit: University of Basel, Department of Physics

Scientists at the University of Basel has recently developed a method that can precisely obtain an individual fingerprint of the current-carrying edge states occurring in novel materials such as topological insulators or 2-D materials. The new technique now makes it possible to obtain an exact fingerprint of the current-carrying edge states with nanometer resolution.

While insulators don’t conduct electrical streams, some unique materials display unconventional electrical properties. In spite of the fact that not leading through their mass, their surfaces and edges may bolster electrical streams because of quantum mechanical impacts, and do as such even without causing losings.

In particular, their robust edge states are very promising since they could lead to great technological advances.

Comparable impacts as the edge conditions of such topological encasings likewise show up when a two-dimensional metal is presented to a solid attractive field at low temperatures. Whenever the purported quantum Hall impact is acknowledged, current is thought to stream just at the edges, where a few directing channels are formed.

Until now, it was not possible to address the numerous current-carrying states individually or to determine their positions separately. The new technique now makes it possible to obtain an exact fingerprint of the current-carrying edge states with nanometer resolution.

Originally, this method is based on tunneling spectroscopy. Scientists also used a gallium arsenide nanowire located at the sample edge which runs in parallel to the edge states under investigation. In this configuration, electrons may jump (tunnel) back and forth between a specific edge state and the nanowire as long as the energies in both systems coincide.

Using an additional magnetic field, the scientists control the momentum of tunneling electrons and can address individual edge states. From the measured tunneling currents, the position and evolution of each edge state may be obtained with nanometer precision.

This new technique is very versatile and can also be used to study dynamically evolving systems. Upon increasing the magnetic field, the number of edge states is reduced, and their distribution is modified. For the first time, the scientists were able to watch the full edge state evolution starting from their formation at very low magnetic fields.

With increasing magnetic field, the edge states are first compressed towards the sample boundary until eventually, they move towards the inside of the sample and then disappear completely. Analytical and numerical models developed by the research team agree very well with the experimental data.

The study is published in the journal Nature Communications.