Ultra-low frequency Raman spectroscopy: a novel optical technology for probing the carrier-phonon interaction in quantum materials

Yu-Ming Chang^1*, Wei-Liang Chen¹, Hui-Yu Cheng^1,2, Wen-Hao Chang², Chin-Shan Lue³

¹Center for Condensed Matter Sciences, National Taiwan University, Taipei City, Taiwan
²Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
³Department of Physics, National Cheng Kung University, Tainan, Taiwan

* Presenter:Yu-Ming Chang, email:ymchang@ntu.edu.tw

Recently, the innovation of ultra-low frequency (ULF) Raman spectroscopy via the implemented Volume Bragg Grating (VBG) filters, has make it a benchtop instrument to routinely measure the Raman spectroscopic information down to 10 cm^-1. Unlike its traditional ULF Raman ancestor, which requires large research system or complex and expensive instrument such as triple-grating monochrometer, this modern ULF Raman technology opens up many new areas of research for material science. For examples, the analysis of lattice modes in pharmaceutical polymorphs, longitudinal acoustic modes (LAM) in polymers or superlattice modes in semiconductor heterostrutures, can now be conveniently investigated with this new version of ULF Raman technology. In this presentation, I would like to share the experience of constructing a VBG filter-based ULF Raman system in our laboratory and demonstrate the applications of this home-built ULF Raman system in two of our recent collaborate research topics. The first one is to realize the interlayer phonon modes of few-layered PdSe₂, which is a species of two-dimensional transition metal dichalcogenides (2D-TMDs). The second one is to investigate the amplitude and phase modes of CuTe single crystal, which is recently identified as quasi-one-dimensional charge density wave (CDW) system at room temperature. In brief, our works demonstrate that ultra-low frequency Raman spectroscopy is a robust and noninvasive optical tool to reveal not only the interlayer stacking configuration of 2D materials, but also the coupling dynamics of CDW and lattice phonon in quantum materials.

Keywords: Ultra-Low Frequency Raman Spectroscopy, Interlayer Interaction, Charge Density Wave, 2D-TMD, Quantum Material