Condensed Matter Physics Seminar

Dr. Elizabeth Blackburn, Birmingham University

Friday 18 October 2013, 1500-1600
C1 Physics Building

"Multiple order parameters in YBCO" - C1, 3pm

The YBa2Cu3Oy family of high temperature superconductors (HTSs) is a very well-studied material. Despite this, YBCO and other HTSs have proven frustratingly hard to understand. Not only the mechanism of superconductivity, but also the origin of normal state properties such as the "pseudogap" phase remaining unresolved. The notion of competing order is central to many theories of unconventional superconductivity, where superconductivity emerges on tuning between phases governed by much larger energy scales. An example of this is the widely-discussed "stripe order" observed in some HTSs and related compounds. It is important to know if this tendency towards stripes is a generic property of cuprates.

In the last year or two, evidence has emerged of an incommensurate charge density wave (CDW) lattice modulation in YBa2Cu3Oy, initially from NMR in high fields, and then by direct observation with hard and soft x-rays. These results, together with transport measurements in this region, indicate that the normal state is very busy. In this seminar, I will survey the various observations of oddities in the normal state, highlighting similarities between different cuprate superconductors, with a particular focus on links to the CDW.