Superconducting gaps and Pseudogaps: spectroscopic evidence for two competing, coexisting phases below Tc

Note: Pizza served at 11:45 AM
Speaker: Vidya Madhavan, Boston College

When: September 19, 2008 (Fri), 12:00PM to 01:00PM (add to my calendar)
Location: SCI 352

This event is part of the Biophysics/Condensed Matter Seminar Series.

Abstract:

The origin of the pseudogap (PG) phase is one of the most important unsolved mysteries of high temperature superconductivity. Explanations for the PG range from fluctuating superconducting (precursor) pairs to a competing phase. A huge hindrance to progress is that in most of the extensively studied superconductors, the PG and superconducting energy scales coincide. In optimally doped Bi2Sr2-xLaxCuO6+δ (La-Bi2201) however, these two energy scales are well separated. Through a comparison study of scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy (ARPES) on La-Bi2201, we report the observation of two distinct gaps that coexist both in real space and in the anti-nodal region of momentum space. The smaller gap can be identified as the superconducting gap while the large gap persists above Tc and can be identified as the PG in these samples. These data provide tantalizing evidence for a competing phase description of the PG in this material. Intriguingly, we find that the pervasive charge ordering in these samples disappears in the overdoped samples concomitant with a suppressed large-gap and a weakened nesting condition, suggesting a causal relationship between them.