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تسجيل مستخدم جديدSuperconductivity by transition metal doping in Ca$_{10}$(Fe$_{1-x}$M$_x$As)$_{10}$(Pt$_3$As$_8$) (M = Co, Ni, Cu)
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We report the successful substitution of cobalt, nickel, and copper for iron in the 1038 phase parent compound Ca$_{10}$(FeAs)$_{10}$(Pt$_3$As$_8$) yielding Ca$_{10}$(Fe$_{1-x}$Co$_x$As)$_{10}$(Pt$_3$As$_8$), Ca$_{10}$(Fe$_{1-x}$Ni$_x$As)$_{10}$(Pt$_3$As$_8$), and Ca$_{10}$(Fe$_{1-x}$Cu$_x$As)$_{10}$(Pt$_3$As$_8$), respectively. Superconductivity is induced in Co and Ni doped compounds reaching critical temperatures up to 15 K, similar to known Pt substituted Ca$_{10}$(Fe$_{1-x}$Pt$_x$As)$_{10}$(Pt$_3$As$_8$), whereas no superconductivity was detected in Ca$_{10}$(Fe$_{1-x}$Cu$_x$As)$_{10}$(Pt$_3$As$_8$). The obtained Tc(x) phase diagrams are very similar to those of other iron arsenide superconductors indicating rather universal behavior despite the more complex structures of the 1038-type compounds, where the physics is primarily determined by the FeAs layer.
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The platinum iron arsenides Ca$_{10}$(Fe$_{1-x}$Pt$_x$As)$_{10}$(Pt$_n$As$_8$) are the first Fe based superconductors with metallic spacer layers. Furthermore they display a large variation in their critical temperatures depending on the amount of Pt
in their spacer layers: $(n=3,4)$. To gain more insight into the role of the spacer layer the electronic structures of the iron arsenic platenides are represented in the momentum space of the underlying Fe sublattice using a first principles unfolding method. We find that Ca$_{10}$(FeAs)$_{10}$(Pt$_4$As$_8$), contrary to Ca$_{10}$(FeAs)$_{10}$(Pt$_3$As$_8$), shows a net electron doping and a non-negligible interlayer coupling. Both effects could account for the difference in the critical temperatures.
Inelastic neutron scattering studies have been carried out on selected phonons and magnetic excitations of a crystal of superconducting (SC) Ca$_{10}$Pt$_4$As$_8$(Fe$_{1-x}$Pt$_x$As)$_{10}$ with the onset transition temperature $T_{rm c}^{rm onset} s
im$ 33 K to investigate the role that orbital fluctuations play in the Cooper pairing. The spectral weight of the magnetic excitations, $chi ({bm Q}, omega)$ at ${bm Q} = {bm Q}_{rm M}$ (magnetic $Gamma$ points) is suppressed (enhanced) in the relatively low (high) $omega$ region. The maximum of the enhancement is located at $omega = omega_{rm p} sim$ 18 meV at temperature $T = 3$ K corresponding to the $omega_{rm p}/k_{rm B}T_{rm c}^{rm onset} sim$ 6.3. This large value is rather favorable to the orbital-fluctuation mechanism of the superconductivity with the so-called $S_{++}$ symmetry. In the phonon measurements, we observed slight softening of the in-plane transverse acoustic mode corresponding to the elastic constant $C_{66}$. This softening starts at $T$ well above the superconducting $T_{rm c}$, as $T$ decreases. An anomalously large increase in the phonon spectral weight of in-plane optical modes was observed in the range of $35 < omega < 40$ meV with decreasing $T$ from far above $T_{rm c}$. Because this $omega$ region mainly corresponds to the in-plane vibrations of Fe atoms, the finding presents information on the coupling between the orbital fluctuation of the Fe 3$d$ electrons and lattice system, useful for studying possible roles of the orbital fluctuation in the pairing mechanism and appearance of the so-called nematic phase.
We report superconductivity in polycrystalline samples of the 1038-type compounds (Ca$_{1-x}$RE$_x$)$_{10}$(FeAs)$_{10}$(Pt$_3$As$_8$) up to T$_c$ = 35 K with RE = Y, La-Nd, Sm, Gd-Lu. The critical temperatures are independent of the trivalent rare e
arth element used, yielding an universal T$_c$($x$) phase diagram for electron doping in all these systems. The absence of superconductivity in Eu$^{2+}$ doped samples, as well as the close resemblance of (Ca$_{1-x}$RE$_x$)$_{10}$(FeAs)$_{10}$(Pt$_3$As$_8$) to the 1048 compound substantiate that the electron doping scenario in the RE-1038 and 1048 phases is completely analogous to other iron-based superconductors with simpler crystal structures.
We report the magnetic field -- temperature ($H-T$) phase diagram of Ca$_{10}$(Pt$_4$As$_8$)[(Fe$_{1-x}$Pt$_x$)$_2$As$_2$]$_5$ ($xapprox 0.05$) single crystals, which consists of normal, vortex liquid, plastic creep and elastic creep phases. The uppe
r critical field anisotropy is determined by a radio frequency technique via the measurements of magnetic penetration depth, $lambda$. Both, irreversibility line, $H_{irr}(T)$, and flux creep line, $H^{SPM}(T)$, are obtained by measuring the magnetization. We find that $H_{irr}(T)$ is well described by the Lindemann criterion with parameters similar to those for cuprates, while small $H^{SPM}(T)$ results in a wide plastic creep regime. The flux creep rates in the elastic creep regime are in qualitative agreement with the collective creep theory for random point defects. A gradual crossover from a single vortex to a bundles regime is observed. Moreover, we obtain $lambda(4~ text K) = 260(26)$ nm through the direct measurement of the London penetration depth by magnetic force microscopy.
Local lattice structures of La$_{1.85}$Sr$_{0.15}$Cu$_{1-x}$M$_x$O$_4$ (M=Mn, Ni, and Co) single crystals are investigated by polarized extended x-ray absorption fine structure (EXAFS). The local lattice instability at low temperature is described by
in-plane Cu-O bond splitting. We find that substitution of Mn for Cu causes little perturbation of local lattice instability while Ni and Co substitution strongly suppresses the instability. The suppression of superconductivity by Cu-site substitution is related to the perturbation of lattice instability, indicating that local lattice instability (polaron) plays an important role in superconductivity.
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