Seminar: Comparative studies of pseudogap physics in Charge Density Wave (CDW) materials and cuprate High Temperature Superconductors (HTSCs)

Time: July 29th, at 10:00am 

Place: CCM seminar room, East 4

Prof. Utpal Chatterjee  

University of Virginia (UVA)  

 

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 Tcthat 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(d) is suppressed as a function of the intercalation-concentrationdand eventually vanishes at a critical value ofd=dcleading 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 Tcor beyonddc.This leads to the persistence of a gap in the electronic spectra in the absence of long-range order, a phenomenonstrikingly similar to the so-called pseudogap in completely different systems such as high temperature superconductors, disordered superconducting thin films and cold atoms.

Short Biography

Dr. Utpal Chatterjee is an assistant professor at the physics department of the University of Virginia (UVA). Before joining to UVA in August 2012, Dr. Chatterjee was a postdoctoral fellow at the Materials Science Division of the Argonne National Laboratory. He completed his PhD from the University of IL at Chicago in December 2007, from Prof. Juan-Carlos Campuzano’s group. Dr. Chatterjee’s main expertise is Angle Resolved Photoemission Spectroscopy, which he employsin the experimental investigations of various solid state systems exhibiting novel electronic and magnetic properties, such as cuprate high temperature superconductors, colossal magneto resistive manganites, different transition metal dichalcogenides hosting charge density wave (CDW) as well as metal insulator (MI) transitions and a number of narrow band gap semiconductors displaying unique topological and thermoelectric properties. He also won the NSF CAREER Award in 2015.