For several decades, improvements in conventional transistor materials have been sufficient to sustain Moore’s Law — the historical pattern of microchip manufacturers packing more transistors (and thus more information storage and handling capacity) into a given volume of silicon. Today, however, chipmakers are concerned that they might soon reach the fundamental limits of conventional materials. If they cannot continue to pack more transistors into smaller spaces, they worry that Moore’s Law would break down, preventing future circuits from becoming smaller and more powerful than their predecessors. Researchers worldwide are seeking new materials that can compute in smaller spaces, primarily by taking advantage of the additional degrees of freedom that the materials offer — using a material’s unique properties to perform more computations in the same space.

Valleytronics, an emerging approach, utilizes the highly selective response of candidate crystalline materials under specific illumination conditions to denote their on/off states; that is, using the materials’ band structures so that the information of 0s and 1s is stored in separate energy valleys of electrons, which are dependent on the crystal structures of the materials.

Valleytronics utilizes different local energy extrema (valleys) with selection rules to store 0s and 1s. This schematic illustrates the variation of electron energy in different states, represented by curved surfaces in space. The two valleys of the curved surface are shown.

New information-handling potential has been discovered in samples of tin(II) sulfide (SnS), a candidate valleytronics transistor material that might one day enable chipmakers to pack more computing power onto microchips. It was demonstrated that tin(II) sulfide (SnS) is able to absorb different polarizations of light and then selectively re-emit light of different colors at different polarizations. This is useful for concurrently accessing both the usual electronic and valleytronic degrees of freedom, which would substantially increase the computing power and data storage density of circuits made with the material.

The material is different from previously investigated candidate valleytronics materials because it possesses such selectivity at room temperature without additional biases apart from the excitation light source, alleviating the previously stringent requirements in controlling the valleys. Compared to its predecessor materials, SnS is also much easier to process.

Researchers will be able to develop operational valleytronic devices that may one day be integrated into electronic circuits. The unique coupling between light and valleys in this new material may also pave the way toward future hybrid electronic/photonic chips.

For more information, contact John German at This email address is being protected from spambots. You need JavaScript enabled to view it.; 510-486-6601.