Second Harmonic Generation Spectroscopic Study of Weyl Semimetal Mn₃Sn with Broken Time-Reversal Symmetry

Topological Weyl semimetals constitute an important class of quantum materials, characterized by a chiral band structure resulting from the breaking of inversion and/or time-reversal symmetries. However, their experimental identification typically relies on techniques such as angle-resolved photoelectron spectroscopy or ultrahigh vacuum scanning tunnelling microscopy which require demanding conditions including low temperatures and ultrahigh vacuum environments. Consequently, there is a growing need for experimental techniques capable of identifying signatures of topological states under ambient conditions. Second-order nonlinear optical processes, such as second harmonic generation (SHG), have emerged as promising tools for studying Weyl semimetals and other topologically nontrivial systems due to their sensitivity to symmetry-breaking effects. However, most previous SHG studies on Weyl semimetals have been limited to systems with broken inversion symmetry or a combination of broken inversion and time reversal symmetries. There has been a scarcity of investigations focusing solely on Weyl semimetals with broken time-reversal symmetry. In this study, we employ reflection SHG measurements to investigate the surface of thin films of the Weyl semimetal Mn₃Sn, which exhibits broken time-reversal symmetry. Our findings demonstrate that the surface SHG response of this system exhibits significant dependence on the excitation wavelength and polarization geometry. These observations provide valuable insights into the understanding of surface electronic properties and spin chirality in these materials. By employing these experimental techniques under ambient conditions, our research contributes to the broader goal of developing efficient methods for characterizing topological states in Weyl semimetals, paving the way for potential applications in electronic and spintronic devices.