What is your favourite quasiparticle?

By James Dacey

This week, an international group of researchers has hit the headlines by reporting the first-ever observation of a quasiparticle called the “orbiton”. First predicted a decade ago, the orbiton can be thought of as an electron in which the properties of spin and charge have been suppressed. Elsewhere in the news this week, a separate team has spotted a quasiparticle that resembles the elusive Majorana fermion predicted in the 1930s by Italian physicist Ettore Majorana.

Quasiparticles can be thought of as excitations in a solid that behave like tiny particles that obey quantum mechanics; a phonon, for example, is a quantized sound wave that propagates through a crystal.

However, the definition of a quasiparticle is not something that is universally accepted – indeed, some argue that a phonon is not a quasiparticle, by virtue of it being a boson rather than a fermion. Others ask whether these “particles” are in fact real physical entities or whether they are merely useful mathematical concepts for understanding the collective behaviour of real particles within bulk materials.

However you want to think about them, quasiparticles have proved themselves to be very useful. For instance, an entire fleet of electronic devices has been developed over the years thanks to our understanding of “holes”, which are quasiparticles representing the absence of an electron.

In this week’s Facebook poll, we want to know if you hold a particular affinity for any of these quasiparticles.

What is your favourite quasiparticle?

Phonon
Spinon
Hole
Exciton
Wrinklon

Have your say by casting your vote on our Facebook page. And feel free to post a comment to explain your choice or to nominate another quasiparticle not on our list.

In last week’s poll, we entered the realm of quantum mechanics, and we received a fantastic response to the question “What is the trickiest feature of quantum mechanics to get your head round?”. The results were as follows.

Entanglement, aka “spooky action at a distance” 65%
The Heisenberg uncertainty principle 13%
Wave–particle duality 11%
Superposition 6%
The Pauli exclusion principle 4%

In addition to the votes, there was also a lively discussion on our Facebook page as people shared their experiences of grappling with the ideas of quantum mechanics. One user who goes by the name of Art Hobson wrote “A close look at wave–particle duality reveals that quantum physics is about fields, not particles. The so-called particles are simply excitations (waves) in these fields.”

Another Facebook user, Wendl Thomis, revealed that the feature of quantum mechanics he has most trouble with is the idea of virtual particles. “Virtual particles are postulated to come into and out of existence at every point of space at dizzying rates so that the energy there can fluctuate as quantum mechanics demands. A very non-intuitive idea,” he says.

Thank you for all your participation and we look forward to hearing from you in this week’s poll.

And if you want to learn more about the ideas of quantum mechanics, take a listen to the latest edition in the Physics World books podcast series, in which we discuss the enduring popularity of quantum mechanics in popular-science writing.