BEGIN:VCALENDAR VERSION:2.0 PRODID:Data::ICal 0.22 BEGIN:VEVENT DESCRIPTION:Utpal Chatterjee\, University of Virginia\n\n
\n Charge densi ty waves (CDWs) and superconductivity are canonical examples of symmetry b reaking in materials. Both are characterized by a complex order parameter &ndash\; namely an amplitude and a phase. In the limit of weak coupling an d in the absence of disorder\, the formation of pairs (electron-electron f or superconductivity\, electron-hole for CDWs) and the establishment of ma croscopic phase coherence both occur at the transition temperature Tc 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 exte nsive experimental investigations on pristine and intercalated samples of 2H-NbSe2\, a CDW material with strong electron-phonon coupling\, using a c ombination of structural (X-ray)\, spectroscopic (photoemission and tunnel ling) and transport probes. We find that Tc(&delta\;) is suppressed as a f unction of the concentration (&delta\;) of the intercalated atoms and even tually vanishes at a critical value of &delta\;=&delta\;c leading to quant um phase transition (QPT). Our integrated approach provides clear signatur es 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 Tc and beyond &delta\;c. This leads to the persist ence of an energy gap in the electronic spectra even though there is no lo ng-range order\, a phenomenon strikingly similar to the so-called pseudoga p in completely different systems such as high temperature superconductors \, disordered superconducting thin films and cold atoms.
\n DTSTART:20150209T203000Z LOCATION:Physics Building\, Room 204 SUMMARY:Phase incoherence driven melting of order parameters in cuprate hig h temperature superconductors and disordered charge density wave systems END:VEVENT END:VCALENDAR