Spectroscopic investigations of pseudogap state in CDW materials and cuprate High Temperature Superconductors HTSCs

by Utpal Chatterjee

at Condensed Matter Seminar

Mon, 09 Nov 2015, 11:30
Physics building (#54) room 207

Abstract

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 Tc that marks the onset of long range order But the situation may be drastically different at strong coupling or in the presence of disorder We have performed extensive experimental investigations on pristine and intercalated samples of 2H NbSe2 a transition metal dichalcogenide CDW material with strong electron phonon coupling using a combination of structural X ray spectroscopic photoemission and tunnelling and transport probes We find that Tc is suppressed as a function of the intercalation concentration and eventually vanishes at a critical value of c 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 Tc or beyond c This leads to the persistence of a gap in the electronic spectra in the absence of long range order a phenomenon strikingly similar to the so called pseudogap in completely different systems such as high temperature superconductors disordered superconducting thin films and cold atoms

Created on 03-11-2015 by Bar Lev, Yevgeny (ybarlev)
Updaded on 03-11-2015 by Bar Lev, Yevgeny (ybarlev)