Raman spectra in iron-based quaternary CeO_1−xF_xFeAs and LaO_1−xF_xFeAs

Abstract

We compute the electronic structure, momentum resolved spectral function and optical conductivity of the new superconductor LaO1−xFxFeAs within the combination of the Density functional theory and the Dynamical Mean Field Theory. We find that the compound in the normal state is a strongly correlated metal and the parent compound is a bad metal at the verge of the metal insulator transition. We argue that the superconductivity is not phonon mediated.

Nonlinear and time-resolved optical study of the 112-type iron-based superconductor parentCa1−xLaxFeAs2across its structural phase transition

“…To date, we are not aware of any Raman spectroscopy studies of the 112-type materials. The other iron-based superconductor families, however, show Raman-active phonons near this energy, including the out-ofplane As A 1g mode at 20 to 25 meV reported in the 111-, 1111-, and 122-type materials [26][27][28][29][30]. A comparable time-resolved reflectivity study using an 800-nm pump reported similar oscillations in Ba(Fe 1−x Co x ) 2 As 2 that they also attributed to the As A 1g mode [25], suggesting the mode as a likely candidate for the reflectivity oscillations observed here.…”

Micro-Raman and infrared study of NdFeAsO0.85

“…At low temperatures (T ≤ 230 K) an extra band appears in the far infrared region at ∼200 cm −1 . The origin of this mode is still unclear since no IR mode is expected to appear in this energy region [16,17] and has never been observed before in the infrared spectra of the RFeAsO family of compounds [3,7,24]. Repeated polishing of the sample did not induce any change in the IR spectra, indicating that the origin of the peak at ∼200 cm −1 is related to the NdFeAsO 0.85 phase.…”

“…Therefore, we believe that the two observed asymmetric peaks are related to four Raman active modes. Based on the assignment done for the RFeAsO family of compounds we conclude that the mode observed at ∼160 cm −1 is of E g -symmetry and is probably connected to the vibrations of As, Fe atoms [16][17][18], the modes at ∼169 cm −1 and ∼203 cm −1 are of A 1g -symmetry and are related to the vibrations of Nd and As atoms, respectively and finally the mode at ∼214 cm −1 is the B 1g -symmetry mode of Fe atoms [16][17][18][19][20]. The peak that appears at ∼278 cm −1 is also related to the Fe vibrations and is of E g -symmetry [16][17][18].…”

“…However, the high energy band at ∼446 cm −1 is very broad and asymmetric, indicating that it is not consisted of only one peak, as reported before [17,21,23], but a second peak at ∼494 cm −1 also appears. The peak at ∼105 cm −1 is probably related to vibrations of Nd atoms, whereas the mode which appears at ∼270 cm −1 is correlated to the vibrations of either the Fe, As atoms or the O atoms [16,17]. The high energy modes at ∼446 cm −1 and ∼494 cm −1 are presumably related to the vibrations of oxygen atoms, since at such high frequencies only these phonon modes are expected to appear [21].…”

Iron isotope effect in SmFeAsO0.65 and SmFeAsO0.77H0.12 superconductors: A Raman study

“…The average frequencies, as we have recorded Raman spectra at many points for each sample and have taken the average, of phonon modes for four different samples are tabulated in Table-I. Following the earlier Raman studies on "1111" systems, [53][54][55][56][57][58][59][60] and based on our observations, we assign the observed phonon modes as S1: ∼ 165 cm -1 (A 1g , Sm); S2 ∼ 200 cm -1 (B 1g , Fe); S3 ∼ 225 cm -1 (A 1g , As); and S4 ∼ 250 cm -1 (E g , Fe and As). Figure 3 shows the comparative Raman spectra of SmFeAsO 0.65 with 54 Fe and 57 Fe substitution.…”