Editing Fermi liquid theory (section)

===Optical response===
Fermi liquid theory predicts that the scattering rate, which governs the optical response of metals, not only depends quadratically on temperature (thus causing the <math>T^2</math> dependence of the DC resistance), but it also depends quadratically on frequency.<ref>{{cite journal|author=R. N. Gurzhi|year=1959|title=MUTUAL ELECTRON CORRELATIONS IN METAL OPTICS|journal=Sov. Phys. JETP|volume=8|pages=673–675}}</ref><ref>{{cite journal|author1=M. Scheffler |author2=K. Schlegel |author3=C. Clauss |author4=D. Hafner |author5=C. Fella |author6=M. Dressel |author7=M. Jourdan |author8=J. Sichelschmidt |author9=C. Krellner |author10=C. Geibel |author11=F. Steglich |year=2013|title=Microwave spectroscopy on heavy-fermion systems: Probing the dynamics of charges and magnetic moments|journal=Phys. Status Solidi B|volume=250|issue=3 |pages=439–449|doi=10.1002/pssb.201200925|arxiv = 1303.5011 |bibcode = 2013PSSBR.250..439S |s2cid=59067473 }}</ref><ref>{{cite journal|author1=C. C. Homes |author2=J. J. Tu |author3=J. Li |author4=G. D. Gu |author5=A. Akrap |year=2013|title=Optical conductivity of nodal metals|journal=Scientific Reports|volume=3|issue=3446 |pages=3446|doi=10.1038/srep03446|pmid=24336241 |pmc=3861800 |arxiv = 1312.4466 |bibcode = 2013NatSR...3.3446H }}</ref> This is in contrast to the [[Drude model|Drude prediction]] for non-interacting metallic electrons, where the scattering rate is a constant as a function of frequency.
One material in which optical Fermi liquid behavior was experimentally observed is the low-temperature metallic phase of [[Sr2RuO4|Sr<sub>2</sub>RuO<sub>4</sub>]].<ref>{{cite journal |author1=D. Stricker |author2=J. Mravlje |author3=C. Berthod |author4=R. Fittipaldi |author5=A. Vecchione |author6=A. Georges |author7=D. van der Marel |year=2014|title=Optical Response of Sr<sub>2</sub>RuO<sub>4</sub> Reveals Universal Fermi-Liquid Scaling and Quasiparticles Beyond Landau Theory |journal= Physical Review Letters|volume=113|issue=8 |pages=087404 |doi=10.1103/PhysRevLett.113.087404 |pmid=25192127 |bibcode=2014PhRvL.113h7404S|arxiv=1403.5445 |s2cid=20176023 }}</ref>