Abstract:

　　Spin-orbit coupling plays an important role in condensed matter physics. It is conventionally viewed as a single-electron property inherited from the Dirac equation but not directly related to many-body interactions. In this talk, we propose a conceptually new mechanism for the spontaneous generation of spin-orbit coupling from unconventional type of magnetic phase transitions (e.g. p-wave) based on itinerant Fermi surface instabilities. The ordered phases are classified into two classes, dubbed the alpha and beta-phases by analogy to the superfluid He-3 A and B phases, respectively. The Fermi surfaces in the alpha phases exhibit spontaneous anisotropic distortions, which are the electronic nematic phases augmented by the spin degree of freedom. The beta-phases remain isotropic and develop nontrivial spin-texture configurations in momentum space – exhibiting various types of spin-orbit coupling. Possible directions for experimentally realizing these phases in transition metal oxides and rare earth compounds, and detections including neutron scattering and optical methods are discussed. We have also systematically developed Fermi liquid theory with spin-orbit coupled but inversion invariant systems, and applied it to Fermi systems characterized by magnetic dipolar interactions. An exotic propagating collective mode is identified as spin-orbit coupled Fermi surface oscillations.

References:

1)  Congjun Wu, and Shou-Cheng Zhang, "Dynamic generation of spin-orbit coupling", Phys. Rev. Lett. 93, 36403 (2004).

2)  Congjun Wu, Kai Sun, Eduardo Fradkin, and Shou-Cheng Zhang, "Fermi liquid instabilities in the spin channel", Phys. Rev. B 75, 115103 (2007).

3) Can-Li Song et al, “Direct Observation of Nodes and Twofold Symmetry in FeSe Superconductor”, Science 332, 1410 (2011).

4)  Yi Li, Congjun Wu, “Spin-orbit coupled Fermi liquid theory with magnetic dipolar interaction”, Phys. Rev. B 85, 205126 (2012)

Biosketch:

　　Congjun Wu received his Ph.D. in physics from Stanford University in 2005, and did his postdoctoral research at the Kavli Institute for Theoretical Physics, University of California, Santa Barbara, from 2005 to 2007. He became an Assistant Professor in the Department of Physics at the University of California, San Diego (UCSD) in 2007, an Associate Professor of Physics at UCSD in 2011, and a Professor of Physics at UCSD in 2017. He became a Chair Professor of Physics at School of Science, Westlake University, Hangzhou in 2021. He was elected to be a Fellow of American Physical Society in 2018. His research interests are exploring new states of matter and reveling their organizing principles, including quantum magnetism, superconductivity, topological states, mathematical physics, and the numerical method of quantum Monte Carlo simulations.