by Helmholtz Association of German Research Centres

Extremely thin materials consisting of just a few atomic layers promise applications for electronics and quantum technologies. An international team led by TU Dresden has now made remarkable progress with an experiment conducted at Helmholtz-Zentrum Dresden-Rossendorf (HZDR): The experts were able to induce an extremely fast switching process between electrically neutral and charged luminescent particles in an ultra-thin, effectively two-dimensional material.

The result opens up new perspectives for research as well as for optical data processing and flexible detectors. The research is presented in the journal Nature Photonics.

Two-dimensional semiconductors can exhibit fundamentally different properties compared to more conventional bulk crystals. In particular, it is easier to generate so-called exciton particles: If an electron, known to be negatively charged, is excited in the material by absorbing energy, it is removed from its original position. It leaves behind a mobile charge¡ªa positively charged "hole."

Electrons and holes attract each other and form together a bound state called an exciton, a kind of electronic pair. If another electron is nearby, it is pulled towards it to form a three-particle state¡ªknown as a trion in scientific jargon. The special feature of the trion is the combination of electrical charge with strong light emission, which allows simultaneous electronic and optical control.

For quite some time, the interplay between exciton and trion has been considered as a switching process that is both intriguing in itself and could also be of interest for future applications. In fact, many laboratories have already succeeded in switching between the two states in a targeted manner¡ªbut so far with limited switching speeds.

The study was led by Prof. Alexey Chernikov from TU Dresden and HZDR physicist Dr. Stephan Winnerl has now been able to significantly accelerate this switching. The work was conducted within the frame of the W¨¹rzburg-Dresden Cluster of Excellence "Complexity and Topology in Quantum Materials, ct.qmat." Researchers from Marburg, Rome, Stockholm and Tsukuba provided important contributions to the project.