Electronic Nematic Phases in Correlated Electron Systems

点击翻译按钮获取中文摘要

When water is cooled it forms ice. The properties of ice and water are dramatically different. The change of state from water to ice is a common example of a "phase transition". When ice forms, the water molecules order and the symmetry of the system is lowered. In this project, we will investigate the properties of a number of systems which have "electronic nematic phases" (ENP's). The materials to be investigated are layered ruthenates and iron-based superconductors. The common feature of the these materials is that the electronic properties (such as the electrical resistance) become anisotropic at low temperatures without a change of crystal symmetry. This suggests that the current carrying electrons (conduction electrons) form a new "ordered" state or electronic nematic phase at low temperature.The importance of electronic nematic phases in condensed mater has been recognized in the last few years. They occur in two dimensional semiconductor materials and the ruthenate material Sr3Ru2O7 at high magnetic field, high-temperature (cuprate) superconductors, and the recently discovered iron-based superconductors. The objective of the present project is to relate the anisotropic electronic behaviour of two types of ENP (iron-based superconductors and ruthenates) to their incipient magnetic properties. We will use neutron and x-ray scattering to investigate the collective magnetic excitations in these materials. Experiments will be performed at international facilities such as the ISIS spallation source in the UK and ILL in France. Our preliminary results suggest that the collective magnetic excitations are key to understanding the ENP behavior in both these systems. New instrumental advances will enable us to create and study the ENP phases in situ for the first time by applying a uniaxial stress or high magnetic field.