Proximity to a commensurate charge modulation in IrTe2−xSex (x = 0 and 0.45) revealed by Raman spectroscopy

Abstract

Optical phonons are employed to probe a structural phase transition of IrTe $_{2-x}$ Se _x at ${{T}_{C}}\sim 280$ K for x = 0 and ${{T}_{C}}\sim 491$ K for x = 0.45, which is dictated by Ir dimerization with charge modulations. Phonon Raman spectra show a discontinuous change at T _C and thermal hysteresis. A $165\;{\rm c}{{{\rm m}}^{-1}}\;{{A}_{g}}$ mode involving out-of-plane motions of Te atoms is mostly affected by Se doping. This highlights the role of interlayer Te–Te interactions in inducing the structural instability. For temperatures below T _C both x = 0 and x = 0.45 compounds exhibit commonly five zone-folded peaks for the $128\;{\rm c}{{{\rm m}}^{-1}}\;{{E}_{g}}$ in-plane mode and six zone-folded peaks for the $165\;{\rm c}{{{\rm m}}^{-1}}\;{{A}_{g}}$ mode. This is taken as a signature of a respective quintupling and sextupling of the unit cell. Our results, on the one hand, are consistent with a 1/5 charge modulation reported by previous studies and, on the other hand, indicate that the ground state of IrTe $_{2-x}$ Se _x lies in proximity to a 1/6 commensurate charge modulation phase.

Keywords

• charge density wave
• structural phase transition
• superstructure