Seminar：Spin driven superconductivity and nematicity in BaFe2-xNixAs2

Time: 4:00-5:00pm, Thursday, June 29th, 2017

Location: Room 242, East 4 teaching building, Zijingang Campus

Huiqian Luo

Instituteof Physics, Chinese Academyof Sciences

Abstract

In this talk, I will present our extensive neutron scattering research on the electron-doped iron pnictide superconductors BaFe2-xNixAs2. It is argued that high-temperature superconductivity in iron pnictides is driven by the short-ranged spin fluctutations similar to other unconventional superconductors such as copper oxides [1, 2]. By mapping out the whole spin spectrum throughout the entire phase diagram of BaFe2-xNixAs2, we have found that the high energy spin fluctuations survive in the extremely high doping x=0.6 far beyond the superconducting dome [3,4], but the low energy spin excitations including the spin resonance mode is very sensitive to the electron dopings [5], finally forming a large spin gap just after the vanishing of zero resistivity or the disappearance of superconductivity in the overdoped regime [1, 3]. Thus the spin dynamics of iron pnictides has both itinerant and localized nature, and low energy spin excitations are crucial to the superconductivity [1]. After apply uniaxial pressure to fully detwin the crystal, a spin nematic phase is found to breaking the C4rotation symmetry in Q space [6], where the nematic order parameter giving by the difference of spin intensity or correlation length behaviors like a second order phase transition described by Landau theory [7]. The spin nematicity has much higher energy scale and robustness against temperature than the orbital order or resistivity anisotropy [8], suggesting such novel phase is driven by spin interactions.

 

References

[1] P. Dai, Rev. Mod. Phys. 87, 855 (2015).

[2] P. D. Johnson et al., Iron-Based Superconductivity, Springer (2015).

[3] M. Wang et al., Nature Commun. 4, 2874(2013).

[4] H. Luo et al., Phys. Rev. B 88, 144516 (2013).

[5] H. Luo et al., Phys. Rev. B 86, 024508 (2012).

[6] X. Lu et al., Science 345, 657 (2014).

[7] W. Zhang et al., Phys. Rev. Lett. 117, 227003 (2016).

[8] Y. Song et al.,Phys. Rev. B 92, 180504 (R) (2015).

Biography of Dr. Huiqian Luo

Dr. Huiqian Luo is an associate professor for condensed matter physics at Institute of Physics, Chinese Academy of Sciences (IOP, CAS), Beijing, China. He graduated from Beijing Normal University in 2004 and completed his PhD program at IOP, CAS in 2009. After that, he join Prof. Pengcheng Dai’s new group at IOP, CAS as an assistant professor for neutron scattering research on novel materials. His scientific interests include single crystal growth, transport studies and neutron scattering on the high temperature superconductors especially on the iron pnictides. Dr. Huiqian Luo have published over 100 research papers with about 2450 citations (H-index= 28) during the first 10 years of his research life.