Abstract:We have measured the reflectivity of the optimally doped Ca8.5La1.5(Pt3As8)(Fe10As10) single crystal (Tc = 32.8K) over the broad frequency range from 40 cm −1 to 12000 cm −1 and for temperatures from 8K to 300 K. The optical conductivity spectra of the low frequency region (< 1, 000 cm −1 ) in the normal state (80 K < T ≤ 300 K) is well fitted with two Drude forms, which indicates the presence of multiple bands at the Fermi level. Decreasing temperature below 80 K, this low frequency Drude spectra develops pse… Show more
“…2) using a larger plasma frequency at 30 K. The penetration depth due to the smaller gap Δ 1 exhibits a smaller penetration depth and dominates the value of the penetration depth within the error bars. Moreover, the variation of the penetration depth with temperature is found to fit very closely to the relation with and The penetration depth at 0 K and are consistent with the result obtained for optimally La-doped Ca10-3-8 samples 12 and the result obtained from the electrical resistivity mentioned above, respectively. The inset of Fig.…”
Section: Resultssupporting
confidence: 88%
“…The plasma frequencies (corresponding scattering rates) were evaluated to be = 1446 cm −1 ( = 20 cm −1 ) for the narrow Drude band and = 6322 cm −1 ( = 125 cm −1 ) for the broad Drude band, respectively. The high-frequency interband transitions are explained by two Lorentz oscillator components, similar to the results for Ca 8.5 La 1.5 (Pt 3 As 8 )(Fe 2 As 2 ) 5 reported previously 12 , with the far-infrared interband transitions well fitted by two Lorentz oscillator components at 150 and 230 cm −1 . In addition, the transition from the Pt 5 d band mentioned above was included in this fitting using a broad Lorentz oscillator at approximately 2000 cm −1 , with the transitions due to the broad band included using two relatively broad Lorentz oscillators at approximately 300 and 600 cm −1 .…”
Section: Resultssupporting
confidence: 87%
“…This inconsistency comes from the uncertainty in the low-frequency extrapolations; thus, to solve this problem of inconsistency, lower-frequency data are required. The gap magnitudes at 8 K are smaller than those for the optimally La-doped 10-3-8 compound 12 ; the magnitude of the smaller gap is reduced by 25%, while that of the larger gap is reduced by 60%. The scattering rates corresponding to the smaller (larger) gaps are similar to those for the broad (narrow) Drude bands shown in Fig.…”
Section: Resultsmentioning
confidence: 66%
“…According to a former suggestion, such differences arise from the difference in the metallicity of the Pt n As 8 layers 14 , with the latter suggestion that the differences can develop from the number of band-edge singularities 15 . To investigate the effect of such subtle differences on the electronic structure and superconductivity, various experimental studies based on transport 11 , pressure effects 16 , NMR 17 , ARPES 18 , neutron 19 , and IR spectroscopy 12 have been carried out; thus, much progress has been made. However, detailed studies on the characteristic changes of superconducting gaps due to such differences in the electronic structure have rarely been carried out, with the in-depth understanding of the superconductivity mechanism, as well as the systematic development of superconductivity, having hardly progressed.…”
We measured the optical reflectivity R(ω) for an underdoped (Ca0.935La0.065)10(Pt3As8)(Fe2As2)5 single crystal and obtained the optical conductivity using the K-K transformation. The normal state at 30 K is well fitted by a Drude-Lorentz model with two Drude components (ωp1 = 1446 cm−1 and ωp2 = 6322 cm−1) and seven Lorentz components. Relative reflectometry was used to accurately determine the temperature dependence of the superconducting gap at various temperatures below Tc. The results clearly show the opening of a superconducting gap with a weaker second gap structure; the magnitudes for the gaps are estimated from the generalized Mattis-Bardeen model to be Δ1 = 30 and Δ2 = 50 cm−1, respectively, at T = 8 K, which both decrease with increasing temperature. The temperature dependence of the gaps was not consistent with one-band BCS theory but was well described by a two-band (hence, two gap) BCS model with interband interactions. The temperature dependence of the superfluid density is flat at low temperatures, indicating an s-wave full-gap superconducting state.
“…2) using a larger plasma frequency at 30 K. The penetration depth due to the smaller gap Δ 1 exhibits a smaller penetration depth and dominates the value of the penetration depth within the error bars. Moreover, the variation of the penetration depth with temperature is found to fit very closely to the relation with and The penetration depth at 0 K and are consistent with the result obtained for optimally La-doped Ca10-3-8 samples 12 and the result obtained from the electrical resistivity mentioned above, respectively. The inset of Fig.…”
Section: Resultssupporting
confidence: 88%
“…The plasma frequencies (corresponding scattering rates) were evaluated to be = 1446 cm −1 ( = 20 cm −1 ) for the narrow Drude band and = 6322 cm −1 ( = 125 cm −1 ) for the broad Drude band, respectively. The high-frequency interband transitions are explained by two Lorentz oscillator components, similar to the results for Ca 8.5 La 1.5 (Pt 3 As 8 )(Fe 2 As 2 ) 5 reported previously 12 , with the far-infrared interband transitions well fitted by two Lorentz oscillator components at 150 and 230 cm −1 . In addition, the transition from the Pt 5 d band mentioned above was included in this fitting using a broad Lorentz oscillator at approximately 2000 cm −1 , with the transitions due to the broad band included using two relatively broad Lorentz oscillators at approximately 300 and 600 cm −1 .…”
Section: Resultssupporting
confidence: 87%
“…This inconsistency comes from the uncertainty in the low-frequency extrapolations; thus, to solve this problem of inconsistency, lower-frequency data are required. The gap magnitudes at 8 K are smaller than those for the optimally La-doped 10-3-8 compound 12 ; the magnitude of the smaller gap is reduced by 25%, while that of the larger gap is reduced by 60%. The scattering rates corresponding to the smaller (larger) gaps are similar to those for the broad (narrow) Drude bands shown in Fig.…”
Section: Resultsmentioning
confidence: 66%
“…According to a former suggestion, such differences arise from the difference in the metallicity of the Pt n As 8 layers 14 , with the latter suggestion that the differences can develop from the number of band-edge singularities 15 . To investigate the effect of such subtle differences on the electronic structure and superconductivity, various experimental studies based on transport 11 , pressure effects 16 , NMR 17 , ARPES 18 , neutron 19 , and IR spectroscopy 12 have been carried out; thus, much progress has been made. However, detailed studies on the characteristic changes of superconducting gaps due to such differences in the electronic structure have rarely been carried out, with the in-depth understanding of the superconductivity mechanism, as well as the systematic development of superconductivity, having hardly progressed.…”
We measured the optical reflectivity R(ω) for an underdoped (Ca0.935La0.065)10(Pt3As8)(Fe2As2)5 single crystal and obtained the optical conductivity using the K-K transformation. The normal state at 30 K is well fitted by a Drude-Lorentz model with two Drude components (ωp1 = 1446 cm−1 and ωp2 = 6322 cm−1) and seven Lorentz components. Relative reflectometry was used to accurately determine the temperature dependence of the superconducting gap at various temperatures below Tc. The results clearly show the opening of a superconducting gap with a weaker second gap structure; the magnitudes for the gaps are estimated from the generalized Mattis-Bardeen model to be Δ1 = 30 and Δ2 = 50 cm−1, respectively, at T = 8 K, which both decrease with increasing temperature. The temperature dependence of the gaps was not consistent with one-band BCS theory but was well described by a two-band (hence, two gap) BCS model with interband interactions. The temperature dependence of the superfluid density is flat at low temperatures, indicating an s-wave full-gap superconducting state.
“…In particular, many attempts have been made to solve the mystery of the role and origin of the pseudogap seen in the temperature region higher than T c . Pseudogap phenomena have also been found in heavy Fermion superconductors 8 and more recently in iron-based superconductors 9,10 . This implies that the pseudogap phenomenon is a common phenomenon in unconventional superconductors.…”
For high-
T
c
superconductors, clarifying the role and origin of the pseudogap is essential for understanding the pairing mechanism. Among the various models describing the pseudogap, the preformed Cooper pair model is a potential candidate. Therefore, we present experimental evidence for the preformed Cooper pair model by studying the pseudogap spectrum observed in the optical conductivity of a Ca
10
(Pt
4
As
8
)(Fe
2
As
2
)
5
(
T
c
= 34.6 K) single crystal. We observed a clear pseudogap structure in the optical conductivity and observed its temperature dependence. In the superconducting (SC) state, one SC gap with a gap size of Δ = 26 cm
−1
, a scattering rate of 1/τ = 360 cm
−1
and a low-frequency extra Drude component were observed. Spectral weight analysis revealed that the SC gap and pseudogap are formed from the same Drude band. This means that the pseudogap is a gap structure observed as a result of a continuous temperature evolution of the SC gap observed below
T
c
. This provides clear experimental evidence for the preformed Cooper pair model.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.