Electric quadrupole second harmonic generation revealing dual magnetic orders in a magnetic Weyl semimetal

Abstract: Broken symmetries and electronic topology are nicely manifested together in the second order nonlinear optical responses from topologically nontrivial materials. While second order nonlinear optical effects from the electric dipole (ED) contribution have been extensively explored in polar Weyl semimetals (WSMs) with broken spatial inversion (SI) symmetry, they are rarely studied in centrosymmetric magnetic WSMs with broken time reversal (TR) symmetry due to complete suppression of the ED contribution. Here, we report experimental demonstration of optical second harmonic generation (SHG) in a magnetic WSM Co${3}$Sn${2}$S${2}$ from the electric quadrupole (EQ) contribution. By tracking the temperature dependence of the rotation anisotropy (RA) of SHG, we capture two magnetic phase transitions, with both the SHG intensity increasing and its RA pattern rotating at $T{C,1}$=175K and $T_{C,2}$=120K subsequently. The fitted critical exponents for the SHG intensity and RA orientation near $T_{C,1}$ and $T_{C,2}$ suggest that the magnetic phase at $T_{C,1}$ is a 3D Ising-type out-of-plane ferromagnetism while the other at $T_{C,2}$ is a 3D XY-type all-in-all-out in-plane antiferromagnetism. Our results show the success of detection and exploration of EQ SHG in a centrosymmetric magnetic WSM, and hence open the pathway towards the future investigation of its tie to the band topology.