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Register a new userSubstitution for Cu in the electron-doped infinite-layer superconductor Sr0.9La0.1CuO2, Ni reduces Tc much faster than Zn
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We report on the effect of substitution for Cu on Tc of electron-doped infinite-layer superconductors Sr0.9La0.1Cu1-xRxO2, R = Zn and Ni. We found that Tc was nearly constant until x = 0.03 for R = Zn, while superconductivity was nearly suppressed for x = 0.02 with dTc/dx = 20 K/% for R = Ni. This behavior is very similar to that of conventional superconductors. These findings are discussed in terms of the superconducting gap symmetry in the cuprate superconductors including another electron-doped superconductor, (Nd,Ce)2CuO4-y.
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We report on measurements of the in-plane magnetic penetration depth lambda_{ab} in the infinite-layer electron-doped high-temperature cuprate superconductor Sr_0.9La_0.1CuO_2 by means of muon-spin rotation. The observed temperature and magnetic field dependences of lambda_{ab} are consistent with the presence of a substantial s-wave component in the superconducting order parameter in good agreement with the results of tunneling, specific heat, and small-angle neutron scattering experiments.
We report $^{63,65}$Cu NQR measurements on slightly underdoped NdBa$_{2}$Cu$_{3}$O$_{6+y}$ single crystals heavily doped by Ni and Zn impurities. Owing to the impurity doping superconductivity is fully suppressed in both cases. The Ni strongly enhances magnetic correlations and induces a wipeout of the NQR signal comparable to that found in stripe ordered lanthanum cuprates. In contrast, the magnetism is suppressed in the Zn doped sample where no wipeout effect is observed and the nuclear spin relaxation rate is reduced. Our findings are in a striking correspondence with the different impact of Ni and Zn impurities on the charge pseudogap evidenced by recent optical data, uncovering thereby a close relationship between the magnetic correlations and pseudogap phenomena.
We have investigated effects of Zn and Ni on the Cu-spin dynamics and superconductivity from the zero-field muon-spin-relaxation (ZF-muSR) and magnetic-susceptibility, chi, measurements for La_2-x_Sr_x_Cu_1-y_(Zn,Ni)_y_O_4_ with x=0.15-0.20, changing y up to 0.10 in fine step. In the optimally doped x=0.15, it has been concluded that the formation of a magnetic order requires a larger amount of Ni than that of Zn, which is similar to our previous results of x=0.13. From the estimation of volume fractions of superconducting (SC) and magnetic regions, it has been found for x=0.15 that the SC region is in rough correspondence to the region where Cu spins fluctuate fast beyond the muSR frequency window for both Zn- and Ni-substituted samples. According to the stripe model, it follows that, even for x=0.15, the dynamical stripe correlations of spins and holes are pinned and localized around Zn and Ni, leading to the formation of the static stripe order and the suppression of superconductivity. These may indicate an importance of the dynamical stripe in the appearance of the high-T_c_ superconductivity in the hole-doped cuprates. In the overdoped regime of x=0.18 and 0.20, on the other hand, the SC region seems to be in rough correspondence to the region where Cu spins fluctuate fast beyond the muSR frequency window, though it appears that the Cu-spin dynamics and superconductivity are affected by the phase separation into SC and normal-state regions.
We have succeeded in synthesizing electron-doped polycrystalline bulk samples of T-La1.8Eu0.2CuO4-yFy (y = 0 - 0.15) by the fluorination of undoped (Ce-free) T-La1.8Eu0.2CuO4 using NH4F. The magnetic susceptibility measurements have revealed that the superconducting transition temperature, Tc, increases with increasing y, exhibits the maximum of 23 K at y = 0.025, and decreases. The dome-like dependence of Tc on the doped carrier concentration in the T-type (La,Eu)-based cuprates is explained in terms of the pairing mediated by spin fluctuations based on the d-p model calculation [K. Yamazaki et al., J. Phys.: Conf. Ser. 871, 012009 (2017)].
The effects of nonmagnetic Zn and magnetic Ni substitution for Cu site on magnetism are studied by measurements of uniform magnetic susceptibility for lightly doped La_{2-x}Sr_xCu_{1-z}M_zO_4 (M=Zn or Ni) polycrystalline samples. For the parent x=0, Zn doping suppresses the N{e}el temperature T_N whereas Ni doping hardly changes T_N up to z=0.3. For the lightly doped samples with T_N~0, the Ni doping recovers T_N. For the superconducting samples, the Ni doping induces the superconductivity-to-antiferromagnetic transition (or crossover). All the heavily Ni doped samples indicate a spin glass behavior at ~15 K.
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