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Coexistence of Ferromagnetic and Stripe Antiferromagnetic Spin Fluctuations in SrCo2As2

Date: 2019-05-27
Time: 10:00
Venue: M253
Speaker: Dr. Yu Li

Louisiana State University, United States 


We use inelastic neutron scattering to study energy and wave vector dependence of spin fluctuations in SrCo2As2, derived from SrFe 2−xCoxAs2 iron pnictide superconductors. Our data reveal the coexistence of antiferromagnetic (AF) and ferromagnetic (FM) spin fluctuations at wave vectors Q AF=(1, 0) and Q FM=(0, 0)/(2, 0), respectively. By comparing neutron scattering results with those of dynamic mean field theory calculation and angle-resolved photoemission spectroscopy experiments, we conclude that both AF and FM spin fluctuations in SrCo2As2 are closely associated with a flatband of the e g orbitals near the Fermi level, different from the t2g orbitals in superconducting SrFe2−xCoxAs2. Therefore, Co substitution in SrFe2−xCoxAs2 induces a t2g to eg orbital switching, and is responsible for FM spin fluctuations detrimental to the singlet pairing superconductivity.

Brief CV of Dr. Yu Li: 

Yu Li earned his PhD in Physics from Rice University in Houston, TX after he graduated from Renmin University with a master's degree. He is now a postdoctoral researcher in Louisiana Consortium for Neutron Scattering and Department of Physics & Astronomy in Louisiana State University.  His past research focused on fundamental interactions between charge, spin, orbital and lattice in iron-based superconductors and the resultant novel quantum phases, for instance, unconventional superconductivity and electronic/spin nematicity. His current interests include searching for topological objects in various non-centrosymmetric magnetic material and studying their dynamic behaviors.