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Theorists' predictions on nanowires experimentally verified

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Published on Thursday, 14 September 2017

Condensed-matter systems play host to a rich variety of composite particles, which are usually referred to as "quasiparticles". It was believed for a long time that, like all elementary particles, quasiparticles could be classified as either fermions or bosons. However, whereas elementary particles always live in our three-dimensional world, condensed-matter systems can be confined to two-dimensional sheets (e.g., in graphene) or one-dimensional tubes (e.g., in nanowires). It turns out that in these reduced dimensions, fermions and bosons are not the only allowed possibilities.

This insight has led to a flurry of research activities in the past decade and has seen its forefathers rewarded in 2016 with the Nobel Prize in Physics. Two quasiparticle species in particular, Majorana fermions and parafermions, have received tremendous attention from both experimental and theoretical physicists in the past ten years.

Physicists in the group of Thomas Schmidt at the University of Luxembourg and their collaborators predicted in 2015 that certain types of parafermions can be realised in a class of materials called two-dimensional topological insulators. Intriguingly, these quasiparticles were predicted to have exactly half the charge of an electron. Building on this work, Chris Pedder, Thomas Schmidt and their collaborators predicted in 2016 and 2017 that those particles should also be observable in semiconductor nanowires, which are much easier to realise in experiments.

One of their main predictions, and thus one of the prerequisites for parafermions, was that strong electron-electron interactions should be able to convert such nanowires from a metallic state to a (partially) insulating state. This prediction has now been verified in experiments by the FZ Juelich in Germany. Working with indium arsenide nanowires, the experimentalists found a characteristic drop in the electric conductance of the wire which fits very well with the theoretical predictions. Even though more experimental challenges remain, these results are an important step towards the first experimental realisation of parafermions.

Qubits as potential application of parafermions

The current interest in Majorana fermions and parafermions is driven by their potential use as qubits, the fundamental components of quantum computers. Until recently, this work was mainly academic. In the past few years, however, major technology companies such as Microsoft, Intel and Google have realised its potential and are now investing large sums of money into quantum computing. Moreover, the European Commission has recently launched a "Quantum flagship" initiative, one of whose aims is to develop a first workable quantum computer, possibly on the basis of parafermions, within the next 10 years.

 

The publication is available on ORBilu: Dynamic response functions and helical gaps in interacting Rashba nanowires with and without magnetic fields

For more information:Signatures of interaction-induced helical gaps in nanowire quantum point contacts