Structural symmetry changes in SmB6 - 2D correlation spectroscopy and principal component analysis

Abstract

2D correlation analysis (2DCOS) and principal component analysis (PCA) have been performed on temperature-dependent Raman spectra from 12 K to 300 K of SmB6 single crystals grown from Boron with a purity of 99.9% (3N) or 99.9999% (6N). Significant differences in the Raman spectra of SmB6(3N) and SmB6(6N) are observed. The Raman active T2g, Eg, and A1g modes of SmB6(3N) are broader and shift to higher wavenumbers compared with those of SmB6(6N). The results of 2DCOS and PCA on temperature-dependent Raman spectra of SmB6(3N) and SmB6(6N) give us further information. We find that all the T2g, Eg, and A1g modes of SmB6(6N) are single bands, while those of SmB6(3N) show all doublet features. The appearance of multiple bands in Raman vibrational modes of SmB6(3N) sample implies that the structure of boron octahedra of the SmB6(3N) has lower symmetry than that of SmB6(6N). Our findings in 2DCOS and PCA of the Raman spectra strongly support the differences in the behavior of SmB6(3N) and SmB6(6N).