Details of phonon modes of YNi2B2C studied by principal component analysis and two-dimensional correlation analysis

We have applied principal component analysis (PCA) and 2D correlation analysis to the temperature-dependent Raman spectra of YNi2B2C single crystals. PCA score plot based on the temperature-dependent B (boron) A1g mode spectra shows that the thermal behavior of the mode can be grouped into two temperature ranges, one in the range of 4–60 K and the other in the range of 100–290 K. It suggests that the difference in the thermal behavior of the B A1g mode occurs at some temperature between 60 and 100 K.The 2D correlation spectra are calculated separately for these two sets of temperature range, and are found to be different from each other. The behavior of the 820 cm−1 mode is different from the other two modes at 890 and 930 cm−1, suggesting that the origin of the 820 cm−1 mode is different from the other two.