Editing Drude model (section)

=== Drude response in real materials ===
The characteristic behavior of a Drude metal in the time or frequency domain, i.e. exponential relaxation with time constant {{mvar|τ}} or the frequency dependence for {{math|''σ''(''ω'')}} stated above, is called Drude response. In a conventional, simple, real metal (e.g. sodium, silver, or gold at room temperature) such behavior is not found experimentally, because the characteristic frequency {{math|{{itco|''τ''}}<sup>−1</sup>}} is in the infrared frequency range, where other features that are not considered in the Drude model (such as [[Electronic band structure|band structure]]) play an important role.<ref name="Dressel" /> But for certain other materials with metallic properties, frequency-dependent conductivity was found that closely follows the simple Drude prediction for {{math|''σ''(''ω'')}}. These are materials where the relaxation rate {{math|{{itco|''τ''}}<sup>−1</sup>}} is at much lower frequencies.<ref name="Dressel" /> This is the case for certain [[Doping (semiconductor)|doped semiconductor]] single crystals,<ref>{{cite journal |author1=M. van Exter |author2=D. Grischkowsky |year=1990 |title=Carrier dynamics of electrons and holes in moderately doped silicon |url=https://shareok.org/bitstream/11244/19898/1/okds_Grischkowsky_PRB_1990-06-15.pdf |journal=[[Physical Review B]] |volume=41 |issue=17 |pages=12140–12149 |bibcode=1990PhRvB..4112140V |doi=10.1103/PhysRevB.41.12140 |pmid=9993669 |hdl-access=free |hdl=11244/19898}}</ref> high-mobility [[2DEG|two-dimensional electron gases]],<ref>{{cite journal |author1=P. J. Burke |author2=I. B. Spielman |author3=J. P. Eisenstein |author4=L. N. Pfeiffer |author5=K. W. West |year=2000 |title=High frequency conductivity of the high-mobility two-dimensional electron gas |url=https://authors.library.caltech.edu/2073/1/BURapl00b.pdf |journal=[[Applied Physics Letters]] |volume=76 |issue=6 |pages=745–747 |bibcode=2000ApPhL..76..745B |doi=10.1063/1.125881}}</ref> and [[Heavy fermion|heavy-fermion metals]].<ref>{{cite journal |author1=M. Scheffler |author2=M. Dressel |author3=M. Jourdan |author4=H. Adrian |year=2005 |title=Extremely slow Drude relaxation of correlated electrons |journal=[[Nature (journal)|Nature]] |volume=438 |issue=7071 |pages=1135–1137 |bibcode=2005Natur.438.1135S |doi=10.1038/nature04232 |pmid=16372004 |s2cid=4391917}}</ref>