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<h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">Kohn-Anomalie</span></h1>
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<div id="mw-content-text" class="mw-body-content mw-content-ltr" lang="de" dir="ltr"><div class="mw-content-ltr mw-parser-output" lang="de" dir="ltr"><p>Die <b>Kohn-Anomalie</b> (nach <a href="Walter_Kohn" title="Walter Kohn">Walter Kohn</a>, der sie 1959 entdeckte<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>) ist eine <a href="Anomalie" title="Anomalie">Anomalie</a> der <a href="Dispersionsrelation" title="Dispersionsrelation">Dispersionsrelation</a> von <a href="Phonon" title="Phonon">Phononen</a>. Es handelt sich dabei um eine <a href="Logarithmus" title="Logarithmus">logarithmische</a> <a href="Divergenz_eines_Vektorfeldes" title="Divergenz eines Vektorfeldes">Divergenz</a> in der Ableitung der Dispersionsrelation. Diese Divergenz kommt von der Wechselwirkung zwischen Phononen und <a href="Elektron" title="Elektron">Elektronen</a> und tritt immer auf der <a href="Fermifl%C3%A4che" class="mw-redirect" title="Fermifläche">Fermifläche</a> auf, sodass man durch Messung der Dispersion auch Informationen über die Fermifläche bekommt.
</p><p>Die Kohn-Anomalie ist u. a. verantwortlich für den <a href="Peierls-%C3%9Cbergang" class="mw-redirect" title="Peierls-Übergang">Peierls-Übergang</a> in eindimensionalen Molekülketten wie <a href="Polyethin" title="Polyethin">Polyethin</a> und den <a href="Jahn-Teller-Effekt" title="Jahn-Teller-Effekt">Jahn-Teller-Übergang</a> in dreidimensionalen <a href="Kristall" title="Kristall">Kristallen</a>. Sie kann eine <a href="Spontane_Symmetriebrechung" title="Spontane Symmetriebrechung">spontane Brechung der Gittersymmetrie</a> aufgrund elektronischer Energieminimierung bewirken.
</p><p>Experimentell nachgewiesen wurde sie zuerst 1961 in der Gruppe von <a href="Bertram_Brockhouse" title="Bertram Brockhouse">Bertram Brockhouse</a> in Chalk River.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>
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<div class="mw-heading mw-heading2"><h2 id="Einzelnachweise">Einzelnachweise</h2></div>
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<li id="cite_note-1"><span class="mw-cite-backlink"><a href="#cite_ref-1">↑</a></span> <span class="reference-text">W. Kohn: <cite style="font-style:italic">Image of the Fermi Surface in the Vibration Spectrum of a Metal</cite>. In: <cite style="font-style:italic">Physical Review Letters</cite>. <span style="white-space:nowrap">Band<span style="display:inline-block;width:.2em"> </span>2</span>, <span style="white-space:nowrap">Nr.<span style="display:inline-block;width:.2em"> </span>9</span>, Mai 1959, <span style="white-space:nowrap">S.<span style="display:inline-block;width:.2em"> </span>393–394</span>, <a href="Digital_Object_Identifier" title="Digital Object Identifier">doi</a>:<span class="uri-handle" style="white-space:nowrap"><a rel="nofollow" class="external text" href="https://doi.org/10.1103/PhysRevLett.2.393">10.1103/PhysRevLett.2.393</a></span>.<span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rfr_id=info:sid/de.wikipedia.org:Kohn-Anomalie&rft.atitle=Image+of+the+Fermi+Surface+in+the+Vibration+Spectrum+of+a+Metal&rft.au=W.+Kohn&rft.date=1959-05&rft.doi=10.1103%2FPhysRevLett.2.393&rft.genre=journal&rft.issue=9&rft.jtitle=Physical+Review+Letters&rft.pages=393-394&rft.volume=2" style="display:none"> </span></span>
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<li id="cite_note-2"><span class="mw-cite-backlink"><a href="#cite_ref-2">↑</a></span> <span class="reference-text">B. N. Brockhouse, K. R. Rao, A. D. B. Woods: <cite style="font-style:italic">Image of the Fermi Surface in the Lattice Vibrations of Lead</cite>. In: <cite style="font-style:italic">Physical Review Letters</cite>. <span style="white-space:nowrap">Band<span style="display:inline-block;width:.2em"> </span>7</span>, <span style="white-space:nowrap">Nr.<span style="display:inline-block;width:.2em"> </span>3</span>, 1. August 1961, <span style="white-space:nowrap">S.<span style="display:inline-block;width:.2em"> </span>93–95</span>, <a href="Digital_Object_Identifier" title="Digital Object Identifier">doi</a>:<span class="uri-handle" style="white-space:nowrap"><a rel="nofollow" class="external text" href="https://doi.org/10.1103/PhysRevLett.7.93">10.1103/PhysRevLett.7.93</a></span>.<span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rfr_id=info:sid/de.wikipedia.org:Kohn-Anomalie&rft.atitle=Image+of+the+Fermi+Surface+in+the+Lattice+Vibrations+of+Lead&rft.au=B.+N.+Brockhouse%2C+K.+R.+Rao%2C+A.+D.+B.+Woods&rft.date=1961-08-01&rft.doi=10.1103%2FPhysRevLett.7.93&rft.genre=journal&rft.issue=3&rft.jtitle=Physical+Review+Letters&rft.pages=93-95&rft.volume=7" style="display:none"> </span><br>B. N. Brockhouse, T. Arase, G. Caglioti, K. R. Rao, A. D. B. Woods: <cite style="font-style:italic">Crystal Dynamics of Lead. I. Dispersion Curves at 100°K</cite>. In: <cite style="font-style:italic">Physical Review</cite>. <span style="white-space:nowrap">Band<span style="display:inline-block;width:.2em"> </span>128</span>, <span style="white-space:nowrap">Nr.<span style="display:inline-block;width:.2em"> </span>3</span>, 1. November 1962, <span style="white-space:nowrap">S.<span style="display:inline-block;width:.2em"> </span>1099–1111</span>, <a href="Digital_Object_Identifier" title="Digital Object Identifier">doi</a>:<span class="uri-handle" style="white-space:nowrap"><a rel="nofollow" class="external text" href="https://doi.org/10.1103/PhysRev.128.1099">10.1103/PhysRev.128.1099</a></span>.<span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rfr_id=info:sid/de.wikipedia.org:Kohn-Anomalie&rft.atitle=Crystal+Dynamics+of+Lead.+I.+Dispersion+Curves+at+100%C2%B0K&rft.au=B.+N.+Brockhouse%2C+T.+Arase%2C+G.+Caglioti%2C+...&rft.date=1962-11-01&rft.doi=10.1103%2FPhysRev.128.1099&rft.genre=journal&rft.issue=3&rft.jtitle=Physical+Review&rft.pages=1099-1111&rft.volume=128" style="display:none"> </span></span>
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