# Massless electrons behave relativistically

1. Nov 9, 2005

### ZapperZ

Staff Emeritus
"Massless" electrons behave relativistically

This is just one of a zoo of examples from condensed matter where relativistic forms manifest themselves via condensed matter phenomena.

http://physicsweb.org/articles/news/9/11/6/1

Just imagine. One could have a benchtop demo of QCD!

Zz.

2. Nov 9, 2005

### Hans de Vries

Nowadays I thrust physicsweb no more than New Scientist or Scientific
American.... Electrons with zero rest-mass moving 100 million times faster
through a solid state material than normal.....?!

This must be signal speed. The explanation would be as follows. If the
string of zeroes are electrons in the graphite and electron A kicks in
resulting in electron B being kicked out at the other side then the speed
of A to B would appear to be extremely high.

A ---> 00000000000000000000000000000000000000000000

------ 00000000000000000000000000000000000000000000 ----> B

They somehow don't see the electrons in the graphite structure as mobile
charge carriers. This coincides with the other bizarre remark that the
conductivity remains even if there are "no mobile charge carriers in the
graphite
".

Current without charge.... ?!

Regards, Hans

3. Nov 10, 2005

### ZapperZ

Staff Emeritus
The DIFFERENCE here from New Scientist etc. is that Physics Web is REPORTING a paper published elsewhere AND that they include the exact citation, something New Scientist and Sci Am are notorious for not consistently doing.

I read the Nature papers (there were TWO separate papers on the same subject in the same issue) and the News and Views on these two papers in the same issue, and the PhysicsWeb article is accurate! These results illustrates the bizzare behavior of what we mean as "charge transport" in 2D material.

And I don't see anything wrong with "current without charge". After all, I have seen current without any bias voltage potential (Josephson current). The fact that these papers are producing unusual results is the reason why they got into Nature in the first place.

Zz.

Last edited: Nov 10, 2005
4. Nov 10, 2005

### inha

The Nature papers were an interesting read. There also was a mention in one of the papers that one or two theory groups had independently predicted the same behaviour so it seems that there's nothing wrong with physicsweb's credibility.

5. Nov 10, 2005

### Hans de Vries

The whole point is that physicsweb talks as if we have to take all these
things literally while the document repeatedly uses the word "fictitious".

This speed of 1 million m/s per second comes from an effective calculation
where $E=m_cc_*^2$ where $c_* = 10^6 m/s$ is called the "effective speed of light".
This is something entirely different then saying that the electrons are actually
moving with this speed.

The two theory groups you mentioned had predicted the Quantum Hall
Effects and not the "behavior" as suggested by physicsweb.

Well, here are the papers.

http://marcuslab.harvard.edu/jc/marcus0510.pdf [Broken]
http://arxiv.org/ftp/cond-mat/papers/0509/0509330.pdf

Regards, Hans

Last edited by a moderator: May 2, 2017
6. Nov 10, 2005

### ZapperZ

Staff Emeritus
But if we're going to pick on that kind of terminology, then you should also pick on condensed matter people who work in "quantum teleportation" and "heavy fermion systems". I mean, when they talk about the electron in UPt having 200 times the mass of a bare electron, they are also talking about "effective mass". One could easily use your argument and accuse them of using "fictitious" notion.

I really don't see this as a problem, and certainly will not fault PhysicsWeb for using it especially the News and Views article in the same issue says the same thing.

Zz.

7. Nov 15, 2005

### Lonewolf

The "relativistic" here means that the energy dispersion relation of a quasiparticle follows $$E = c^{*} P$$, rather than the usual dispersion relation $$E = \frac{P^2}{2m_{eff}}$$, with P being the momentum of a quasiparticle and $$m_{eff}$$ the effective mass of the quasiparticle.

From this, the quasiparticle shows signs of effective relativistic phenomena, rather than the non-relativistic effects shown by the quasiparticles experiencing the ordinary dispersion relation.