Title: Topological spin excitations in CrI₃

Time: Thursday, 16:00-17:00 pm, Dec. 5^th, 2019

Location: Yuquan Campus, Teaching Building 12, Room 201 

Abstract: In two-dimensional honeycomb ferromagnets, bosonic magnon quasiparticles (spin waves) may either behave as massless Dirac fermions or form topologically protected edge states. The key ingredient defining their nature is the next-nearest-neighbor Dzyaloshinskii-Moriya interaction that breaks the inversion symmetry of the lattice and discriminates chirality of the associated spin-wave excitations. Using inelastic neutron scattering, we find that spin waves of the insulating honeycomb ferromagnet CrI3 (T_C= 61 K) have two distinctive bands of ferromagnetic excitations separated by a ∼4 meV gap at the Dirac points. These results can only be understood by considering a Heisenberg Hamiltonian with DzyaloshinskiiMoriya interaction, thus providing experimental evidence that spin waves in CrI₃ can have robust topological properties potentially useful for dissipationless spintronic applications.  

About the Speaker:  

Prof. Pengcheng Dai obtained his BS degree from Zhengzhou University in 1984 and his Ph. D degree in 1993 from University of Missouri. He is currently a professor of Physics at Rice University.  He is a APS, AAAS fellow, and winner of 2016 sustained prize winner of neutron scattering society of America. He works neutron scattering studies of correlated electron materials, and has a google scholar citation of > 21000. He is also a divisional associate editor, physical review letters.