“Valleytronics” – quantum electronics in diamond

5.00/5 (1)

Diamond is a semiconductor with extreme properties, such as high breakdown field, high saturation velocity, high carrier mobilities and the highest thermal conductivity of all materials. This makes diamond extreme in the group of wide-bandgap semiconductors, which includes e.g., silicon carbide (SiC) and gallium nitride (GaN).

Diagramme from: http://www.el.angstrom.uu.se/forskningsprojekt/Diamant/Diamant_E.html

 (“Valleytronics” – a new type of electronics in diamond – Phys.org) —An alternative and novel concept in electronics is to utilize the wave quantum number of the electron in a crystalline material to encode information. In a new article in Nature Materials, Isberg et.al. propose using this valley degree of freedom in diamond to enable valleytronic information processing or as a new route to quantum computing.

In electronic circuits, bits of information (1:s and 0:s) are encoded by the presence or absence of electric charge. For fast information processing, e.g. in computer processors or memories, charges have to be moved around at high switching rates. Moving charges requires energy, which inevitably causes heating and gives rise to a fundamental limit to the switching rate.

As an alternative it is possible to utilize other properties than the charge of electrons to encode information and thereby avoid this fundamental limit. An example of this is “spintronics” where the spin of the electron is used to carry information.

An alternative and novel concept is to utilize the wave quantum number of an electron in a crystalline material. This may lead to ultrafast computing with less power consumption. In a new article in Nature Materials, a group at Uppsala University, consisting of Jan Isberg, Markus Gabrysch, Johan Hammersberg, Saman Majdi and Kiran Kumar Kovi, together with Daniel Twitchen at Element Six Ltd in Britain, show that it is possible to generate, transport and detect electrons with a given valley quantum number in diamond at a temperature of 77 Kelvin.

Electrons travel through crystals as waves. These waves can be described by different quantum numbers such as their crystal momentum and spin. In vacuum, an electron attains its minimum energy for zero momentum but in a crystalline material this may not be so. In diamond, an electron has its minimum energy for a finite value of momentum along certain directions of high symmetry in the crystal. At low temperatures electrons will reside in these valleys of minimum energy, of which there are six in diamond.