Quantcast
  • Register
PhysicsOverflow is a next-generation academic platform for physicists and astronomers, including a community peer review system and a postgraduate-level discussion forum analogous to MathOverflow.

Welcome to PhysicsOverflow! PhysicsOverflow is an open platform for community peer review and graduate-level Physics discussion.

Please help promote PhysicsOverflow ads elsewhere if you like it.

News

New printer friendly PO pages!

Migration to Bielefeld University was successful!

Please vote for this year's PhysicsOverflow ads!

Please do help out in categorising submissions. Submit a paper to PhysicsOverflow!

... see more

Tools for paper authors

Submit paper
Claim Paper Authorship

Tools for SE users

Search User
Reclaim SE Account
Request Account Merger
Nativise imported posts
Claim post (deleted users)
Import SE post

Users whose questions have been imported from Physics Stack Exchange, Theoretical Physics Stack Exchange, or any other Stack Exchange site are kindly requested to reclaim their account and not to register as a new user.

Public \(\beta\) tools

Report a bug with a feature
Request a new functionality
404 page design
Send feedback

Attributions

(propose a free ad)

Site Statistics

145 submissions , 122 unreviewed
3,930 questions , 1,398 unanswered
4,853 answers , 20,624 comments
1,470 users with positive rep
501 active unimported users
More ...

Why is the majorana particle a fermion?

+ 4 like - 0 dislike
66 views

My knowledge of quantum mechanics is rather limited, but what I always understood was that Bosons have integer spins and Fermions have half-integer spins.

My question is very simple: the Majorana particle has no spin according to this paper and this Physics Today article which (without wanting to go into a philosophical mathematical discussion) I would call integer spin. That would make the particle a Boson. So what is the reason that the particle is classified as a Fermion?

This post imported from StackExchange Physics at 2014-04-15 16:37 (UCT), posted by SE-user Michiel
asked Feb 19, 2013 in Theoretical Physics by Michiel (80 points) [ no revision ]
Do you have a source for the statement that Majorana particles have no spin?

This post imported from StackExchange Physics at 2014-04-15 16:37 (UCT), posted by SE-user Chris White
Here: arxiv.org/abs/1209.5115 or here: physicstoday.org/resource/1/phtoad/v65/i6/p14_s1 In particular, the last post has a sentence saying: "As quasiparticles go, the Majorana is incredibly featureless: It’s chargeless, spinless, massless, and without energy"

This post imported from StackExchange Physics at 2014-04-15 16:37 (UCT), posted by SE-user Michiel
Michael, you're actually wrong. Majorana fermions are defined as fermions that are complex conjugate to themselves, but they don't have to be created by spinor fields. In fact, the arxiv.org/abs/1209.5115 case has spinless Majorana fermions, indeed. This would contradict the spin-statistics theorem in a Lorentz-invariant theory but this condensed-matter application isn't Lorentz-invariant, so one may encounter spinless fermions.

This post imported from StackExchange Physics at 2014-04-15 16:37 (UCT), posted by SE-user Luboš Motl
Dear Lubos, could you elaborate your comment a bit (perhaps in a full-blown answer) because I am not sure whether I completely understand your comment. You say they are spinless, because they can be complex conjugates without creation by spinor fields. Then what is it that causes them to be complex conjugates?

This post imported from StackExchange Physics at 2014-04-15 16:37 (UCT), posted by SE-user Michiel
@LubošMotl I stand corrected. I was coming from a particle physics perspective, unfamiliar with the conventions in condensed matter. I deleted my old comment to avoid future confusion.

This post imported from StackExchange Physics at 2014-04-15 16:37 (UCT), posted by SE-user Michael Brown

1 Answer

+ 6 like - 0 dislike

Majorana fermions are by definition fermions which are their own antiparticles, i.e. the do have spin and it's 1/2. An introduction to these fermions can be for example found here: http://arxiv.org/abs/0806.1690. In contrast bosons are their own antiparticles, e.g. photons, i.e. one does not need a "Majorana-boson" definition.

Now, one has to say that these Majorana fermions have not been observed in nature except as quasiparticle excitations in seminconductors.

This post imported from StackExchange Physics at 2014-04-15 16:37 (UCT), posted by SE-user A friendly helper
answered Feb 19, 2013 by A friendly helper (320 points) [ no revision ]
"one has to say that these Majorana fermions have not been observed in nature except [...]" Well, we've observed neutrinos and don't yet know if they are Dirac or Majorana, so let's say "have not been demonstrably observed" or some such weasel word.

This post imported from StackExchange Physics at 2014-04-15 16:37 (UCT), posted by SE-user dmckee

Your answer

Please use answers only to (at least partly) answer questions. To comment, discuss, or ask for clarification, leave a comment instead.
To mask links under text, please type your text, highlight it, and click the "link" button. You can then enter your link URL.
Please consult the FAQ for as to how to format your post.
This is the answer box; if you want to write a comment instead, please use the 'add comment' button.
Live preview (may slow down editor)   Preview
Your name to display (optional):
Privacy: Your email address will only be used for sending these notifications.
Anti-spam verification:
If you are a human please identify the position of the character covered by the symbol $\varnothing$ in the following word:
p$\hbar$ys$\varnothing$csOverflow
Then drag the red bullet below over the corresponding character of our banner. When you drop it there, the bullet changes to green (on slow internet connections after a few seconds).
To avoid this verification in future, please log in or register.




user contributions licensed under cc by-sa 3.0 with attribution required

Your rights
...