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Building quantum dots with single metal atoms

Posted: 04 Feb 2014     Print Version  Bookmark and Share

Keywords:University of Warsaw  quantum dot  magnetic ion 

Faculty of Physics researchers at the University of Warsaw (FUW) have used cobalt for the first time surrounded by cadmium telluride (CdTe) and claimed they may be able to improve the performance by a factor of 10.

In quantum dots where tellurium is replaced by the lighter selenium, researchers observed that the duration for which information was remembered increased by an order of magnitude. This finding suggests that using lighter elements should prolong the time quantum dots containing single magnetic ions store information, perhaps even by several orders of magnitude.

"We have demonstrated that two quantum systems that were believed not to be viable in fact worked very effectively. This opens up a broad field in our search for other, previously rejected combinations of materials for quantum dots and magnetic ions," said Wojciech Pacuski at the Institute of Experimental Physics at FUW.

Researchers are able to control the behavior of individual atoms by situating them within special semiconductor structures; this is the method used to form quantum dots that contain single magnetic ions. Until recently, only two variants of such structures were known. However, physicists from the have successfully created and studied two completely new types of the structures.

"Quantum dots are semiconductor crystals on a nanometer scale. They are so tiny that the electrons within them exist only in states with specific energies. As such, quantum dots exhibit similar characteristics to atoms, and, just like atoms, they can be stimulated with light to reach higher energy levels. Conversely, this means they emit light as they return to states with lower energy levels," noted Piotr Kossacki at FUW.

The University laboratory creates quantum dots using molecular beam epitaxy and by carefully selecting materials and experimental conditions, the atoms assemble into quantum dots.

"Atoms with magnetic properties disrupt the energy levels of electrons in a quantum dot, which affects how they interact with light. As a result, the quantum dot becomes a detector of such an atom's state. The relationship also works the other way: by changing energy states of electrons in quantum dots, we can affect the respective magnetic atoms," said Micha? Papaj, a student at FUW.

The most powerful magnetic properties are observed in manganese atoms stripped of two electrons (Mn2+). In experiments conducted thus far, the ions have been mounted in quantum dots made of cadmium telluride (CdTe) or indium arsenide (InAs).

"It was commonly believed that other magnetic ions, such as cobalt (Co2+), cannot be used in quantum dots. We decided to verify this, and nature gave us a pleasant surprise: the presence of a new magnetic ion turned out not to destroy the properties of the quantum dot," stated Jakub Kobak, doctoral student at FUW.

- Nick Flaherty
  EE Times Europe

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