Vacancy ordering and phonon spectrum of the iron-based superconductor K0.8Fe1.6Se2

Abstract

We have performed Raman-scattering measurements on a high-quality single crystal of the recently discovered Fe-based superconductor K0.8Fe1.6Se2 (Tc = 32 K). At least thirteen phonon modes were observed in the wave number range 10−300 cm −1 . The spectra possess a four-fold symmetry indicative of bulk vacancy order in the Fe-deficient planes. We perform a vibration analysis based on first-principles calculations, which both confirms the ordered structure and allows a complete mode assignment. We observe an anomaly at Tc in the 180 cm −1 Ag mode, which indicates a rather specific type of electron-phonon coupling.

Effect of iron content and potassium substitution inA0.8Fe1.6Se2Zhang1, Liu2, He3 et al. 2012Phys. Rev. BSelf Cite174120View full textAdd to dashboardCite

“…The corresponding symmetry analysis allows a total of 17 A g or B g modes. 12 We have calculated the nonmagnetic electronic structure and the zone-center phonons of K 0.8 Fe 1.6 Se 2 from first principles by performing density-functional calculations.…”

“…This abundance of optical modes arises due to the symmetry reduction caused by Fe vacancy ordering, which we have identified as being from D 4h to C 4h . 12 The space group of the undepleted, 122-type structure, I4/mmm, is reduced to I4/m, a process in which all inplane, two-fold rotation axes and all mirror planes perpendicular to the (ab)-plane are lost. Both the phonon mode energies and the polarizations observed in Fig.…”

“…IV was performed by adjusting the polarization of the incident and scattered light, rather than by a formal symmetry analysis, as discussed in detail in Ref. 12.…”

Low-frequency Raman modes and electronic excitations in atomically thin MoS2films

“…The vibrational frequencies and displacement patterns of phonon modes were calculated at the equilibrium structures using the dynamical matrix method as described in our previous publication. 16 It is worth noting that although the LDA method neglects the van der Waals component of the interaction between the layers, it produces reasonably well the inter-layer phonons of MoS 2 . 17…”

Vacancy-induced nanoscale phase separation in KxFe2−ySe2Lazarević1, Abeykoon2, Stephens3 et al. 2012Phys. Rev. B487620View full textAdd to dashboardCite

“…Zhang et al 12 performed partial assignment, 11 out of 18 Raman-active modes predicted by factor-group analysis (FGA) within the I4/m symmetry group. They found that only one mode around 180 cm −1 exhibits a change in frequency around T c .…”