Analysis of Raman modes of YNi 2B 2C by two-dimensional correlation spectroscopy

Abstract

In this study, we have applied two-dimensional (2D) correlation analysis to the temperature-dependent Raman spectra of superconducting YNi 2B 2C single crystal. The 2D correlation analysis on apparently single peak B 1g phonon mode near 200 cm −1 shows that the peak is essentially composed of two modes at 197 and 203 cm −1, and only the weight of the two modes changes as the temperature changes. This finding is an example of the power of the 2D correlation analysis on resolving highly overlapped peaks in Raman spectra. The finding of two overlapped peaks’ nature of B 1g phonon mode suggests that there are two distinctive environments of the Ni–B bonds in YNi 2B 2C system. Therefore, we extended 2D correlation analysis to the boron A 1g mode in the range of 800–950 cm −1 in a hope to see multiple boron modes like the Ni mode. The 2D correlation analysis of the boron A 1g indeed shows that the peak is composed of multiple (three) peaks at 840, 900, and 930 cm −1. Furthermore, 2D hetero-spectral correlation analysis was employed to relate the origins of the multiple phonon modes of YNi 2B 2C. Synchronous 2D hetero correlation spectrum obtained from the temperature-dependent Raman spectra of the Ni B 1g and B A 1g modes shows that a Ni B 1g phonon mode at 197 cm −1 and B A 1g mode at 840 cm −1 have one origin, while a Ni B 1g phonon mode at 203 cm −1 and B A 1g modes at 900 and 930 cm −1 arise from the other origin.