Abstract
Optical phonons are employed to probe a structural phase transition of IrTe2-xSex at T-C similar to 280 K for x = 0 and T-C similar to 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 cm(-1) A(g) 1 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 cm(-1) E-g 1 in-plane mode and six zone-folded peaks for the 165 cm(-1) A(g) 1 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 IrTe2-xSex lies in proximity to a 1/6 commensurate charge modulation phase.