Phonons and Spin Excitations in Fe-Based Superconductor Ca₁₀Pt₄As₈ (Fe_1−xPt_xAs)₁₀ (x ∼ 0.2)

Abstract

By means of neutron inelastic scattering, magnetic excitations and phonons were measured for a single crystal of slightly overdoped superconductor Ca 10 Pt 4 As 8 (Fe 1−x Pt x As) 10 (x ∼ 0.2) with the transition temperature T c of ∼33 K. Below T c , magnetic excitation spectra χ"(Q, ω) measured at Q = Q M [magnetic Γ points] are gapped, and in the relatively higher ω region, the χ"(Q M , ω)-increase was observed with decreasing T , where the maximum of the increase was found at ∼18 meV at 3 K (<< T c ). These characteristics are favorable to orbital-fluctuation-mediated superconductivity with the so-called S ++ symmetry of the order parameter. The energy dependence of δQ-temperature(T ) curve of the magnetic excitations seems to have anomalous behavior in rather wide T region above T c , δQ being the width of the Q scan profile. In the phonon measurements, we observed softening of the in-plane TA mode, which corresponds to the elastic constant C 66 . This softening seems to start at rather high temperature T , as T is lowered. Additionally, anomalous increase in spectral weights of the TO-phonons at around Q M in the region 35 < ω < 40 meV was found even above T c , as T is lowered from ambient T . Because the spectral weights in this ω region mainly correspond to the in-plane motions of Fe atoms and because orbital fluctuations are expected to be strong at around Q M , the result may present clues to investigate a possible coupling between the fluctuations of the orbitals and lattice system.

Superconducting properties and pseudogap from preformed Cooper pairs in the triclinic(CaFe1−xPtxAs)10Pt3

“…This interpretation motivated us to perform NMR measurements on the same sample, which we will present below, substantiating the presence of a pseudogap with comparable magnitude also in the electronic structure. It is illustrative to compare our INS results with those obtained previously on the related (CaFe 1−x Pt x As) 10 Pt 4 As 8 compounds with higher values of T c [15,48]. In the 10-4-8 sample with T c ≈ 30 K investigated by Sato et al, a peak in χ (Q,ω) was found at an energy of ∼12 meV, which gained intensity upon cooling without exhibiting any clear anomaly at T c , as evidenced by Fig.…”

“…Energies of the low-temperature intensity maxima observed in 10-3-8 and 10-4-8 arsenides from Refs. [15,48] and the present work are plotted for comparison to demonstrate that their ω 0 /k B T c ratios are systematically higher than those expected for the magnetic resonant modes. the usual superconducting resonant mode, but universal among the whole class of materials.…”

“…It is illustrative to compare our INS results with those obtained previously on the related (CaFe 1−x Pt x As) 10 Pt 4 As 8 compounds with higher values of T c . 15,44 In the 10-4-8 sample with T c ≈ 30 K investigated by Sato et al, a peak in χ (Q, ω) was found at an energy of ∼ 12 meV, which gained intensity upon cooling without exhibiting any clear anomaly at T c , as evidenced by Fig. 5 in Ref.…”

Spin fluctuations in iron pnictides and chalcogenides: From antiferromagnetism to superconductivity

“…A clear redistribution of spectral weight below T c could be also seen in polycrystalline "1111"-type pnictides, such as LaFeAsO 0.92 F 0.08 [119] and CaFe 0.88 Co 0.12 AsF [126]. Of particular interest is the anomalous behavior of the magnetic resonance in the "10-4-8" [121,370] and "10-3-8" [318] iron-platinumarsenide compounds. While resonance-like peaks have been observed in these systems at the usual (π, 0) wave vector, their unusually large hω res /k B T c ratios (see Table 2) and their persistence above T c are not typical for…”

Neutron Spin Resonance in the 112-Type Iron-Based Superconductor

“…The spin resonance is argued to arise from the sign-reversed (s±) quasiparticle excitations between different Fermi surfaces in these multiband systems [33][34][35]. Such a mechanism should yield a sharp resonant peak with an energy below the total superconducting gaps summed on the nesting bands [9,26,33], while some exceptions in particular compounds with a broad enhancement of intensity and E R > 2∆ are argued to be the sign-preserved (s ++ ) superconducting state [27][28][29][30][31][32]. The proximity to the AF order and spin-orbital coupling give further complexity on the energy and momentum distribution of spin resonance [12][13][14][15][16][17][18][19][20][21].…”