Nonlinear Optical Detection of Dual Magnetic Ground States in a Magnetic Weyl Semimetal Co₃Sn₂S₂

The symmetry properties of ground states of material systems lie at the essence of condensed matter physics. Nonlinear second harmonic generation techniques have successfully characterized crystallographic point groups, but mostly on systems without inversion symmetry using the leading-order electric dipole contribution. The symmetry studies of recently realized topological centrosymmetric semimetal systems are in demand to provide a clear understanding of their ground states and electronic band topology. In this talk, rotational anisotropy (RA) second harmonic generation (SHG) study of the magnetic Weyl semimetal Co₃Sn₂S₂ will be presented to resolve the debate on its magnetic ground state. In this study, the RA SHG patterns of this centrosymmetric compound are identified to contribute from the leading-order electric quadrupole. By tracking temperature dependence of the RA SHG with the focus on the intensity (time-reversal invariant) and orientation (time-reversal broken), out-of-plane ferromagnetism at <i>T</i>_C,1 = 175 K and in-plane antiferromagnetism at <i>T</i>_C,2 = 120 K are revealed, both belonging to -3m' magnetic point group. Finally, the critical exponents of ferromagnetic and antiferromagnetic order parameters are extracted from the intensity and orientation of the RA SHG, which are represented by even and odd powers of order parameters, respectively, providing insight into the characteristics of these two phase transitions.