Professor Eric Hudson
Department of Physics
MIT

 

Gaps in Our Understanding of High Temperature Superconductors

One of the main challenges in the study of the cuprates is to disentangle the rich variety of states of matter that may coexist, cooperate, or compete with d-wave superconductivity. At center stage is the pseudogap phase, which occupies a large portion of the cuprate phase diagram surrounding the superconducting dome. In this talk I will present results of our recent temperature and doping dependent scanning tunneling microscopy investigations of Bi₂Sr₂CuO_6+x (Bi-2201). First I will focus on the existence of a new, narrow, homogeneous gap that vanishes near TC, superimposed on the typically observed, inhomogeneous, broad gap, which is only weakly temperature dependent [1]. Its existence, especially in combination with recent ARPES and Raman measurements, points strongly toward a picture of the high temperature superconductors in which distinct superconducting and pseudogaps coexist below TC. I will then discuss spatial 'checkerboard' patterns which have been widely observed in the cuprates. We have found a distinct doping dependence of this checkerboard pattern indicating that a charge density wave is its cause [2]. Taken together, these results suggest a need to rethink the nature of pseudogap and its relation to high temperature superconductivity.

1. "Imaging the two gaps of the high-temperature superconductor Bi₂Sr₂CuO_6+x," M. C. Boyer et al, Nat. Phys. 3, 802 (2007).
2. "Charge-density-wave origin of cuprate checkerboard visualized by scanning tunnelling microscopy," W.D. Wise et al, Nat. Phys. 4, 696 (2008).