Credit: © 2007 APS

'Phase-change' materials can rapidly and reversibly switch between amorphous and crystalline structures and are widely used for data storage in DVDs and CD-ROMs. However, such materials only enable the formation of two logic states, which limits the density of data storage.

Now, Nikolay Zheludev and colleagues1 of the University of Southampton in the UK show they can switch between four distinct crystalline states in an 80 nm particle of polymorphic gallium, which was deposited at the centre of a cooled fibre tip from a beam of atomic gallium. Data can be stored and read optically: laser pulses induce changes in the crystal structure of the particles, which are read as shifts in their optical reflectivity.

The gallium nanoparticles will enable data storage of 0.2 terabits per square inch, which is an order of magnitude larger than commercial blue-laser-based DVDs and on a par with perpendicular storage media in hard disks. Moreover, the nanoparticle memory requires only a tenth of the energy to write information compared with cutting-edge optical-storage technology.