This week, Seamus Davis, a leader in the field of scanning tunneling microscopy (STM) was in town and gave a series of talks on the many materials examined in his laboratory by his various students and postdocs. The most compelling of the talks was presented on the pseudogap phase of the high-temperature cuprate superconductors.
According to Davis, the mysterious nature of the pseudogap phase is due to the presence of a density wave with d-form factor, pictured below. In the topographic STM images of BSCCO and NaCCOC, one can see a vivid visual representation of this density wave (link to the paper PDF!).
Because STM is a surface sensitive probe, the high-Tc community always had niggling doubts about whether this density wave was manifest in the bulk. With increasing evidence that there is a density wave in the bulk from scattering probes such as resonant soft X-ray scattering and from hard x-ray diffraction, the interpretation put forth by Davis seems more plausible than it did a decade ago.
He also claimed in this talk that the presence of this density wave could explain the existence of Fermi arcs seen using angle-resolved photoemission, another surface sensitive technique. However, the observation of quantum oscillations in the underdoped cuprates demonstrating pockets at the Fermi surface complicates matters somewhat. For these two observations to be consistent, the only possible explanation is a phase transition in the underdoped cuprates as a function of magnetic field in the region of ~20 Tesla.
Nonetheless, Davis’ group has done a wonderful set of experiments on these compounds and his talks this week were captivating and enjoyable. This seems like a valuable contribution into the ongoing discussion of the mystery of the pseudogap.