View source for Talk:Fermi liquid theory

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== Untitled ==
Are you sure that in order for the ground state of a many-body system to behave as a Fermi liquid, the ''original'', i.e. bare (unrenormalized) interaction must be weak? I always thought that the whole point of the Fermi liquid is that ''in spite of having strong interaction between particles'' we end up with a renormalized state that is almost free. .<!-- Template:Unsigned IP --><small class="autosigned">—&nbsp;Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/80.98.200.27|80.98.200.27]] ([[User talk:80.98.200.27#top|talk]])  12:45, 4 November 2005‎  (UTC)</small>
== Fermi liquid vs. non-Fermi liquid ==

IMHO author made very big mistake in the definition of Fermi liquid. There are some other quantum liquids which are not Fermi liquids despite the fact thet are composed of fermions.

Fermi liquid is theoretical model for describing interacting Fermions. One of the many models (see e.g. Luttinger liquid), co that's not true it is generic for Fermi liquids.

[[User:62.179.49.22|62.179.49.22]] 18:43, 15 March 2006 (UTC)

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To answer the first question, who cares about the bare interaction? When you renormalize towards the Fermi surface all interactions are irrelevant, except the attractive ones in the BCS channel (i.e., scattering of pairs to pairs, with equal and opposite momenta). The ground state is therefore fundamentally altered: it becomes superconducting. This is true in 2D and 3D.

On the other hand, what one can describe as almost free is the quasiparticles, i.e., the fermionic excitations around the Fermi surface. This you can always do if the interaction is repulsive, unless you move well away from the Fermi surface (e.g. at non-zero temperatures), in which case the role of such surface becomes less important and the description in terms of quasiparticles breaks down (quasiparticles become unstable). In other words, Fermi statistics helps us by 'Pauli blocking' the states into which our particles may scatter; as a result, they cannot interact, i.e., they behave as if free. If the interaction is attractive, and weak, then the fermionic excitations will look more like correlated pairs, a.k.a. Cooper pairs, up to the critical temperature. The case of strong attractive interaction is at present under intense theoretical and experimental study, including the so-called unitary or resonant Fermi gas, where the scattering length is infinite. There is consensus that correlated pairs survive well above the critical temperature, up to the dissociation temperature.

In 1D the situation is different, as the Fermi surface is not really a surface (as in 3D) or a line (as in 2D), but collapses to two points: -k_F and k_F. It is in this context that one has the so-called Luttinger liquids. Maybe one should say that a Luttinger liquid is just one type of Fermi liquid, as it involves fermions in 1D, but I don't think there is agreement about this. People tend to think of Luttinger liquids as a fundamentally different kind as the properties of these liquids are very different from those of their higher dimensional partners.

== Cleanup ==

I've done some tidying up (headings, links etc.) but I'm not a physicist so I don't know whether the article is correct.  Does anyone object if I remove the Cleanup tag?  [[User:Biscuittin|Biscuittin]] ([[User talk:Biscuittin|talk]]) 23:24, 19 February 2008 (UTC)

== Refs == 

Ref 18 is an example in the field, but probably we can find much better and more important examples (I suspect this one has never been cited in the literature)  <!-- Template:Unsigned IP --><small class="autosigned">—&nbsp;Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/163.1.19.1|163.1.19.1]] ([[User talk:163.1.19.1#top|talk]]) 08:44, 14 May 2017 (UTC)</small> <!--Autosigned by SineBot-->

== Resistance ==

I assume this means thermal resistance, rather than electrical resistance. Can anyone confirm this? [[User:Biscuittin|Biscuittin]] ([[User talk:Biscuittin|talk]]) 09:42, 20 February 2008 (UTC)

It is the electrical resistance that is usually measured in a lab. So I believe that its electrical resistance that one specifies while talking about Fermi liquids  <small>—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/128.163.161.103|128.163.161.103]] ([[User talk:128.163.161.103|talk]]) 16:35, 31 May 2008 (UTC)</small><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->

It is electrical resistance that is being talked about, although the thermal resistance can also be computed from the theory.  <span style="font-size: smaller;" class="autosigned">— Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/130.102.172.3|130.102.172.3]] ([[User talk:130.102.172.3|talk]]) 01:11, 6 February 2012 (UTC)</span><!-- Template:Unsigned IP --> <!--Autosigned by SineBot-->

== Fermi sea ==
There is a redirection from Fermi sea to this article, although the two notions are different. [[User:Clement.analogue|Clement.analogue]] ([[User talk:Clement.analogue|talk]]) 19:47, 28 August 2009 (UTC)

== Description ==

What is ω in the Green's function? What is difference between ω and є?  <span style="font-size: smaller;" class="autosigned">— Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/133.1.150.32|133.1.150.32]] ([[User talk:133.1.150.32|talk]]) 05:34, 29 November 2011 (UTC)</span><!-- Template:Unsigned IP --> <!--Autosigned by SineBot-->

== Cite Landau's Paper ==
why do we not cite Landau's original paper? it is fairly readable.<!-- Template:Unsigned IP --><small class="autosigned">—&nbsp;Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/82.17.71.110|82.17.71.110]] ([[User talk:82.17.71.110#top|talk]]) 18:45, 25 April 2019 (UTC)</small>
:Sure it could be useful. May you provide a link? --[[User:MaoGo|MaoGo]] ([[User talk:MaoGo|talk]]) 18:47, 25 April 2019 (UTC)

== Misleading name? ==

The name Landau-Fermi liquid theory may be misleading, because may be interpreted as a theory by Landau and Fermi, which is not the case. Perhaps one could write Landau Fermi-liquid theory, instead.

Probably the best is to just delete the parenthesis and say that Fermi-liquid theory is a theory by Landau.