Novel magnetic excitations in iron-based superconductors

By Tom Sharp on May 11, 2017

Iron based superconductors are attracting a huge amount of research in the condensed matter community due to their unconventional superconductivity. In their recent paper in Journal of Physics: Condensed Matter, Hai-Yang Zhang and Ning Xu shed some light on magnetic excitations in iron pnictides to understand this behavior. Read on to find out more from the authors themselves.

The unconventional superconductivity found in iron-based materials has attracted much attention in recent years. Due to the proximity of superconductivity and the magnetic phase, it was believed that the magnetic fluctuations are responsible for the emergence of superconductivity. The magnetic phase is usually accompanied by a nematic order in various materials. Thus, an understanding of the behavior of magnetic excitations in the normal and nematic phases could uncover the mechanism of the unconventional superconductivity.

A plot of the energy evolution of the normal state magnetic excitations for different fillings. Taken from J. Phys. Cond. Mat. 195601 © IOP Publishing 2017.

In our theoretical study, we found that these magnetic excitations exhibit rich structure in energy-momentum space. In the low energy region, commensurability to diamond and to square structure transition occurs with the increase of energy. While in the high energy region, a collective magnetic mode with a sharp peak develops. Further study is required to fully understand the effect of this mode. Furthermore, we show that the main features of the magnetic excitations persist in the spin and orbital driven nematic phases, although anisotropy develops due to the presence of the nematic orders. The anisotropy exhibits distinct energy evolution behavior between the spin and orbital scenarios of nematic phases. This can be used to determine the origin of the nematic phase in iron-based superconductors.

About the Authors

Haiyang Zhang is a lecturer in Theoretical Physics at Yancheng Institute of Technology, China. He obtained his PhD degree from Nanjing University of China in 2013, and then became a postdoctoral fellow at Nanjing University until he joined Yancheng Institute of Technology in 2016. His research is focused on the strongly correlated systems, especially the unconventional superconductivity.

Ning Xu completed his PhD in condensed matter physics from Xiangtan University, China, in 2010. He was then appointed as a senior research associate at Department of Physics and Materials Science in City University of Hong Kong. In October 2015, he established Applied Physics Laboratory at Yancheng Institute of Technology, supported by Chen, the Dean of the faculty of Physics. In the last several years, his research is focused on topological insulator and quantum transport in mesoscopic systems.