Spin 1/2 in the classical and quantum limits: from band topology to spin entanglement

Abstract of the talk

In this talk, I will present two experimental studies both about insulating Cu-based compounds with spin-1/2 magnetic lattices. In the first experiment, we use inelastic neutron scattering to detect a new type of Dirac points in the magnon bands of a 3D antiferromagnet, Cu₃TeO₆. These Dirac points are the limiting case of nodal lines with nontrivial Z₂-monopole charge recently proposed in theory, and they are new to the zoo of experimentally observed topological band crossings. The highly interconnected spin network of Cu₃TeO₆ is essential to the success of our experimental observation, because it strongly suppresses quantum fluctuations.

The second study focuses on 1D spin chains with competing interactions. In the classical limit, the competition gives rise to spiral magnetic order, which is indeed found below T_N in the material we studied. Distinct from this expected result, I will present evidence for short-range spin-singlet formation, accompanied by lattice deformation (or charge order), at intermediate temperatures. The singlet pattern appears to have the same incommensurate wave vector along the chains as the spin spirals, but they exhibit competition across T_N. Our result implies a possible flavor of spin entanglement to unusual charge order in low-dimensional spin-1/2 magnets, such as the high-T_c cuprates.

Biography of the speaker

Dr. Yuan Li obtained his B.S. degrees from Peking University in 2004 and Ph.D. degree from Stanford University in 2010. From 2010 to 2012, he was a Humboldt Research Fellow at the Max Planck Institute for Solid State Research, Germany. He is currently an associate professor at the International Center for Quantum Materials, Peking University. Dr. Li’s research interests include phase behaviors and elementary excitations in correlated-electron materials. To determine these fundamental properties, his research group employs a broad range of scattering methods including neutron and X-ray scattering at public science facilities, as well as in-house Raman spectroscopy.