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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Georgia","serif"">Please join us today for the CME Seminar presented by Utpal Chatterjee from the University of Virginia at 11:30am in the Smith Seminar Room (1080 PRB).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Georgia","serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:12.0pt;font-family:"Georgia","serif"">“</span></b><b><span lang="EN-GB" style="font-size:12.0pt;font-family:"Georgia","serif"">Phase incoherence driven melting of CDW order across quantum and thermal phase transitions
in intercalated 2H-NbSe<sub>2 </sub>system</span></b><b><span style="font-size:12.0pt;font-family:"Georgia","serif"">”<o:p></o:p></span></b></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:12.0pt;font-family:"Georgia","serif"">Charge density waves (CDWs) and superconductivity are canonical examples of symmetry breaking in materials. Both are characterized by a complex order parameter –
namely an amplitude and a phase. In the limit of weak coupling and in the absence of disorder, the formation of pairs (electron-electron for superconductivity, electron-hole for CDWs) and the establishment of macroscopic phase coherence both occur at the transition
temperature T<sub>c</sub> that marks the onset of long-range order. But, the situation may be different at strong coupling or in the presence of disorder. We have performed extensive experimental investigations on pristine and intercalated samples of 2H-NbSe<sub>2</sub>,
a CDW material with strong electron-phonon coupling, using a combination of structural (X-ray), spectroscopic (photoemission and tunnelling) and transport probes. We find that T<sub>c</sub>(d) is suppressed as a function of the intercalation-concentration
d and eventually vanishes at a critical value of d=d<sub>c</sub> leading to quantum phase transition (QPT). Our integrated approach provides clear signatures that the phase of the order parameter becomes incoherent at the quantum/ thermal phase transition,
although the amplitude remains finite over an extensive region above T<sub>c</sub> or beyond d<sub>c</sub>.
</span><span style="font-size:12.0pt;font-family:"Georgia","serif"">This leads to the persistence of a gap in the electronic spectra in the absence of long-range order, a phenomenon
</span><span lang="EN-GB" style="font-size:12.0pt;font-family:"Georgia","serif"">strikingly similar to the so-called pseudogap in completely different systems such as high temperature superconductors, disordered superconducting thin films and cold atoms.
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Georgia","serif"">Thank you,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Georgia","serif"">Trisch<o:p></o:p></span></p>
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