Talk:Semimetal

Definition

The definition for semimetal was taken from Burns, Gerald (1985). Solid State Physics, 339-40, Academic Press, Inc. ISBN 0-12-146070-3. Previously, this page had redirected to metalloid, and I don't believe the two are synonomous. eaolson 00:26, 14 June 2006 (UTC)[reply]

I agree eaolson. They are not. As I learned the definition of semimetal (I'm Solid State Chemist)a semimetal is a semiconductor with a negative indirect bandgap and the standard example was tin (usually not considered a metalloid). Metalloids are elements on the diagonal in the periodic table that can very well be semiconductors with a positive bandgap (direct or indirect).

Semimetals are not necessarily elements and although they behave a lot like metals they differ from them because they have conduction from both holes and electrons (in different parts of the Brilouin zone). Metals typically have one kind of carriers. 152.1.193.141 19:10, 6 August 2006 (UTC) nl:Gebruiker:Sokpopje[reply]

or better

nl.wiktionary Gebruiker:Jcwf

I made a little schematic diagram of a direct semiconductor (A), indirect semiconductor (B) and a semimetal (C) that may be of use. It's a bit primitive but the best I can do.

Jcwf

File:Semimetal.JPG

Could you please save this as a PNG or GIF instead of a JPEG? Don't simply convert it from JPEG, but export the original drawing as a PNG without going through JPEG compression at all. —Keenan Pepper 20:38, 6 August 2006 (UTC)[reply]

OK I'll try, but I am not good at these things sorry

Thanks. See how the hazy ripples are gone? Also the PNG is about half the size of the JPEG. I added it to the article but you might want to improve the caption. —Keenan Pepper 23:59, 6 August 2006 (UTC)[reply]

What has a negative direct bandgap? -lysdexia 02:30, 3 October 2006 (UTC)

Gallium(III) arsenide for example, I would think. I've never really heard anyone use the term "negative bandgap," though. eaolson 02:33, 3 October 2006 (UTC)[reply]

I think the claim that in metals there is only one type of charge carrier (used repeatedly here on the talk page as well as in the article) is not valid. I would say that in a metal, where the Fermi surfaces extend throughout the Brillouin zone, the distinction between holes and electrons is not meaningful. Take a semimetal (with holes and electrons), and shift the higher band down, giving you higher and higher densities at the Fermi level. This is then a metal, while if you would want to classify the charge carriers, you would still get both kinds, or not? Seattle Jörg (talk) 09:55, 12 April 2016 (UTC)[reply]

Jörg, I agree. One of the big giveaways is that metals can have negative or positive Seebeck coefficients, and negative or positive Hall coefficients. In other words they can act either as super-doped p-type semiconductors or super-doped n-type semiconductors. And if you look at the electron dispersion relation of a metal it has negative effective mass in some places but positive effective mass in other places, on the same Fermi surface!

From one point of view there is no such things as holes; then, all materials only have electrons as charge carriers. Even semiconductors.

From another point of view we break down into "electron-holes" and "electron-fills". That's fine for a semiconductor or semimetal, but metals cannot be classified in this way. --Nanite (talk) 17:28, 12 April 2016 (UTC)[reply]

Well, you can say that there are no holes, but instead negative effective mass electrons. With a negative effective mass, they move the opposite direction when there is a force on them, but it is easier for most people to consider them as positive mass positive charged holes. Many metals have both electron and hole bands, aluminium being a popular one. At high magnetic fields, the Hall coefficient goes positive. Gah4 (talk) 18:38, 4 November 2020 (UTC)[reply]

momentum space & k-vector

A few sentences defining these:

momentum space
k-vector,

or links to their definition elsewhere, would be most useful to the general reader. -- Yellowdesk 00:43, 20 March 2007 (UTC)[reply]

Agreed; a pointer to a text or paper with a treatise on the subject would greatly facilitate the usage of this topic not only to the general reader but physical chemistry students as well (me).Bobxii (talk) 01:13, 29 June 2008 (UTC)[reply]

re: merge with half-metal

These should definitely not be merged as they are two distinct and essentially unrelated concepts. Half metals are metals with complete spin polarization of the conduction band. This is in no way related to the concept of a semimetal. —Preceding unsigned comment added by 128.32.117.77 (talk) 03:45, 7 February 2009 (UTC)[reply]

band gap size

The value of 4 eV quoted as "e.g." the delimiter between semiconductors and insulators is misleadingly excessive. Practically only diamond has more than 4 eV, and even silicium is a pretty good insulator, with a gap of 1.1 eV, which is why it needs to be doped for applications. 1 eV is 11600 Kelvin, which gives an idea of the suppression of carrier density at room temperature (300 K) by the Nernst factor, e^(-42.5) for Si. Nimdaz (talk) 11:09, 9 December 2011 (UTC)[reply]

Topological semimetals

I think a section on the comparatively newfangled topic of "topological semimetals" -- Dirac and Weyl semimetals, see e.g. https://arxiv.org/abs/1610.07866 -- somewhere here is appropriate. At the very least we could have a link to the currently somewhat sorry article on Weyl semimetals. Unless there are objections, it's on my to-do list. Dunready (talk) 03:54, 23 February 2017 (UTC)[reply]