SECOND HARMONIC SPECTROSCOPIC STUDIES ON TWO-DIMENSIONAL PDTE₂ DIRAC SEMIMETAL

Syed Mohammed Faizanuddin^1,2,3*, Yu-Chieh Wen¹, Yao-Jui Chan¹, Chin Shuan Lue⁴, Chia-Nung Kuo⁴

¹Institute of Physics, Academia Sinica, Taipei City, Taiwan
²Taiwan International Graduate Program, Academia Sinica, Taipei City, Taiwan
³Department of Engineering and System Science, National Tsing Hua University, Hsinchu City, Taiwan
⁴Department of Physics, National Cheng Kung University, Tainan, Taiwan

* Presenter:Syed Mohammed Faizanuddin, email:faizan@gate.sinica.edu.tw

2D Dirac Semimetals (DSMs), such as ATe₂ (A=Pd, Pt, Ni) are proving to be excellent candidates for developing future optoelectronic and spintronic devices because of their exotic properties including electron transport, topological phase transitions, and superconductivity. However, scientific understanding of these materials concerning their surface structural symmetry, transient behavior, and optical response is still quite limited. Addressing these questions and their influence on the exotic behavior of DSMs carries fundamental and technological significance. Second-harmonic generation (SHG) is a nonlinear optical process in which the induced polarization is proportional to the material’s complex second-order nonlinear susceptibility (χ⁽²⁾). Being a second-order process, SHG is bulk-forbidden for centrosymmetric materials like ATe₂ but is allowed at the surface/interface where the inversion symmetry is broken. Therefore, the SHG technique can be effectively utilized to study the optical response of the surface monolayer of ATe₂ crystals. Here we would like to report our SHG characterizations studies on PdTe₂ DSM.
In the preliminary experiment, SHG response as a function of sample azimuthal angle for various polarization combinations of input and output electric fields were obtained for PdTe₂ crystal. Theoretical fits calculated from these preliminary results infer that the PdTe₂ surface has C_3v symmetry. The results also show qualitatively different SHG response for a freshly cleaved surface from that of a long-term exposed surface, hinting towards the presence of a strong transient behavior. Further, quantitative analyses of the complex χ⁽²⁾ and the time-dependent evolution of the SHG signal of PdTe₂ will be discussed in the talk.

Keywords: Dirac Semimetals, Nonlinear Optics, SHG, PdTe₂, Ultrafast Laser Spectroscopy