Charles Tam: Charge correlations in unconventional superconductors

Abstract:The cuprate family of high Tc superconductors are formed of 2D layers of CuO2. While not being an exclusive feature of this crystal structure, superconductivity is seen in many isostructures of cuprates, such as ruthenates and nickelates. With this similarity in structure comes similarities in their physics. The theme of this talk is the study of the charge correlations using resonant inelastic Xray scattering (RIXS), in particular when these correlations approach zero energy and have most significance to the physical properties.

In this talk I will highlight two such endeavours. First, using RIXS we show the presence of quasi-static charge density waves (CDW) in a very electronically clean cuprate Tl2Ba2CuO6+δ. The CDW can explain aspects of the anomalously low normal state carrier density by inducing a Fermi surface reconstruction. Next, using a simple RPA model, that uses only experimentally measured values as input, we interpret RIXS measurements of the acoustic plasmon in several layered superconductors, including La2-xSrxCuO4 and Tl2Ba2CuO6+δ. We show the acoustic plasmon can, for the most part, be understood in the RPA as an out of phase charge oscillation between neighbouring planes.