Study: Solution to 10-year-old mystery in the way nanoscale transistors work

In this puzzle the tiles are analogous to electrons, while the missing tile is analogous to a hole. Image: By Micha L. Rieser, Attribution,
Sunday, 10 December, 2017
Errol Hunt

Scientists have reconciled experiments and theory about how nanoscale transistors work, paving the way for future quantum electronic and quantum computing devices.

About half of all the transistors in an iPhone use positively charged holes to operate, rather than negatively charged electrons.

Undergraduates are taught that holes are basically missing electrons, a bit like bubbles in a spirit level, or the missing chair in a game of musical chairs.

But that isn't the whole story. Holes have very different spin properties than electrons. (A particle’s spin is its intrinsic angular momentum.)

These unique spin properties of holes make them very attractive for ultra-low powered spin transistors, high-speed quantum bits, and fault-tolerant topological quantum bits.

The problem was that the spin properties of holes in nanoscale transistors were not well understood. In fact, the best theories predicted the opposite behaviour to that observed in experiments, which were originally performed at UNSW and later replicated internationally.

Now a team of physicists led by UNSW's Scientia Professor Alex Hamilton and Professor Olev Sushkov has solved the mystery by identifying a new term in the equations that had previously been overlooked.

Their study is published in the journal Physical Review Letters, the flagship journal of the American Physical Society. The team also includes researchers in Cambridge and Sheffield in the UK, and Novosibirsk in Russia,.

The original study in 2006, also led by Professor Hamilton and published in Physical Review Letters, found that the direction of an applied magnetic field determined the splitting of conductivity in a current of holes. The same effect does not occur in a current of electrons.

See an animation here.

Professor Hamilton and Professor Sushkov are member of FLEET, the ARC Centre of Excellence in Future Low-Energy Electronics Technologies – a  new ARC-funded research centre aiming to address a growing computing energy challenge by using materials that are just one atom in thickness.

See more information about this research here.