Rutgers University Physics/Astronomy Colloquium - Speaker / Title Corrected

The Berry phase is a geometric phase in quantum mechanics1. It underscores many interesting topological phenomena, especially various quantized or extraordinary Hall effects [1,2]. The quest for quantum Hall effect (QHE) without external magnetic field leads to the exciting development of quantum spin Hall effect (QSHE) [3], the emergence of topological classification of band insulators [4], and eventually the realization of quantum anomalous Hall effect (QAHE) [5]. In parallel to the fascinating evolution of Berry phase phenomena in the momentum space, there is also a real space counterpart, the topological Hall effect (THE) which is associated with non-coplanar spin textures with scalar spin chirality. As such, the THE provides a powerful probe of the ground state and low-energy excitations of magnetic metals. I will present our recent research progress on the QAHE and the THE in magnetic thin films using magnetic imaging technique with in-situ transport [6,7]. References
1. Xiao, D., Chang, M. C. & Niu, Q. Berry phase effects on electronic properties. Rev. Mod. Phys. 82, 1959–2007 (2010).
2. Nagaosa, N., Sinova, J., Onoda, S., MacDonald, A. H. & Ong, N. P. Anomalous Hall effect. Rev. Mod. Phys. 82, 1539–1592 (2010).
3. Kane, C. L. & Mele, E. J. Z2 topological order and the quantum spin Hall effect. Phys. Rev. Lett. 95, 146802 (2005).
4. Fu, L., Kane, C. L. & Mele, E. J. Topological Insulators in Three Dimensions. Phys. Rev. Lett. 98, 106803 (2007).
5. Chang, C.-Z. et al. Experimental Observation of the Quantum Anomalous Hall Effect in a Magnetic Topological Insulator. Science (80-. ). 340, 167–170 (2013).
6. Wang, W. et al. Direct evidence of ferromagnetism in a quantum anomalous Hall system. Nat Phys 14, 791–795 (2018).
7. Wang, W. et al. Chiral fluctuation driven topological Hall effect in a two-dimensional uniaxial ferromagnet. submitted, (2018).