Spinonics

In electronics the movement of electrons in a circuit can be exploited to store data, perform calculations, and to excite the playback or broadcast of music. In spintronics one exploits, in addition to the electron's charge, the electron's spin.

What if one could have just the spin and not the charge? " Spinonics" is the term coined by Ganapathy Baskaran of the Institute of Mathematical Sciences in Madras, India, to describe the manipulation of special chargeless parcels of spin known as "spinons" (also called "triplet excitons" when the value of the spin equals 1).

In general collective excitations are to condensed matter physics what elementary particles are to high energy physics. Spin excitations have been seen in condensed matter physics before: spin waves are disturbances which can propagate a spin orientation from one atom to another through a lattice.

But what Baskaran (baskaran@imsc.ernet.in, 0091-44-254-1856) is proposing is an actual current of spin moving from place to place. Triplet excitons, as a packet of spin, can be produced in semiconductors or insulators, but don't go very far and require special techniques and lasers for their generation.

Baskaran and his colleague S. A. Jafari predict a spin current could, however, be created easily and propagate over long distances in graphite and carbon nanotubes, which are both semi-metals: basically semiconductors but ones in which the energy gap (the energy difference between electrons retained by the carbon atoms and electrons free to roam about) is essentially zero.

The advantages of a spin-only form of transport would include the chance to explore new quantum effects and a reduction in undesirable scattering from defects, impurities, and phonons. (Baskaran and Jafari, Physical Review Letters, 1 July 2002.)