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Register a new userPhase diagram and superconducting dome of infinite-layer $mathrm{Nd_{1-x}Sr_{x}NiO_{2}}$ thin films
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Infinite-layer Nd1-xSrxNiO2 thin films with Sr doping level x from 0.08 to 0.3 were synthesized and investigated. We found a superconducting dome to be between 0.12 and 0.235 which is accompanied by a weakly insulating behaviour in both underdoped and overdoped regimes. The dome is akin to that in the electron-doped 214-type and infinite-layer cuprate superconductors. For x higher than 0.18, the normal state Hall coefficient ($R_{H}$) changes the sign from negative to positive as the temperature decreases. The temperature of the sign changes monotonically decreases with decreasing x from the overdoped side and approaches the superconducting dome at the mid-point, suggesting a reconstruction of the Fermi surface as the dopant concentration changes across the center of the dome.
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We report the phase diagram of infinite layer Pr$_{1-x}$Sr$_{x}$NiO$_2$ thin films synthesized via topotactic reduction from the perovskite precursor phase using CaH$_2$. Based on the electrical transport properties, we find a doping-dependent superconducting dome extending between $x$ = 0.12 and 0.28, with a maximum superconducting transition temperature $T_{rm{c}}$ of 14 K at $x$ = 0.18, bounded by weakly insulating behavior on both sides. In contrast to the narrower dome observed in Nd$_{1-x}$Sr$_{x}$NiO$_2$, a local $T_{rm{c}}$ suppression near $x$ = 0.2 was not observed for the Pr$_{1-x}$Sr$_{x}$NiO$_2$ system. Normal state Hall effect measurements indicate mixed carrier contributions of both electrons and holes, and show a sign change in the Hall coefficient as functions of temperature and $x$, quite similar to that in Nd$_{1-x}$Sr$_{x}$NiO$_2$. Also similar is the observation of a minimum in the normal state resistivity associated with the superconducting compositions. These findings indicate an infinite layer nickelate phase diagram that is relatively insensitive to the rare-earth element, but suggest that disorder arising from the variations of the ionic radii on the rare-earth site affects the superconducting dome.
We report the Ni-doping effect on magnetism and superconductivity (SC) in an Eu-containing 112-type system Eu(Fe$_{1-x}$Ni$_{x})$As$_{2}$ ($0leq xleq 0.15$) by the measurements of resistivity, magnetization, and specific heat. The undoped EuFeAs$_2$ undergoes a spin-density-wave (SDW) transition at $T_mathrm{SDW}sim$ 105 K in the Fe sublattice and a magnetic ordering at $T_mathrm{m}sim$ 40 K in the Eu sublattice. Complex Eu-spin magnetism is manifested by a spin-glass reentrance at $T_mathrm{SG}sim$ 15 K and an additional spin reorientation at $T_mathrm{SR}sim$ 7 K. With Ni doping, the SDW order is rapidly suppressed, and SC emerges in the Ni-doping range of 0.01 $leq xleq$ 0.1 where a maximum of the superconducting transition temperature $T_mathrm{c}^{mathrm{max}}=$ 17.6 K shows up at $x$ = 0.04. On the other hand, $T_mathrm{m}$ decreases very slowly, yet $T_mathrm{SG}$ and $T_mathrm{SR}$ hardly change with the Ni doping. The phase diagram has been established, which suggests a very weak coupling between SC and Eu spins. The complex Eu-spin magnetism is discussed in terms of the Ruderman-Kittel-Kasuya-Yosida interactions mediated by the conduction electrons from both layers of FeAs and As surrounding Eu$^{2+}$ ions.
Low energy polarized electronic Raman scattering of the electron doped superconductor Nd_1.85Ce_0.15CuO_4 (T_c=22 K) has revealed a nonmonotonic d_{x^2-y^2} superconducting order parameter. It has a maximum gap of 4.4 k_BT_c at Fermi surface intersections with antiferromagnetic Brillouin zone (the ``hot spots) and a smaller gap of 3.3 k_BT_c at fermionic Brillouin zone boundaries. The gap enhancement in the vicinity of the ``hot spots emphasizes role of antiferromagnetic fluctuations and similarity in the origin of superconductivity for electron- and hole-doped cuprates.
The recent observation of superconductivity in infinite-layer nickelate Nd$_{0.8}$Sr$_{0.2}$NiO$_{2}$ has received considerable attention. Despite the many efforts to understand the superconductivity in infinite-layer nickelates, a consensus on the underlying mechanism for the superconductivity has yet to be reached, partly owing to the challenges with the material synthesis. Here, we report the successful growth of superconducting infinite-layer Nd$_{0.8}$Sr$_{0.2}$NiO$_{2}$ films by pulsed-laser deposition and soft chemical reduction. The details on growth process will be discussed.
We have used the electric--field effect to modulate the resistivity of the surface of underdoped Sr$_{0.88}$La$_{0.12}$CuO$_{2+x}$ thin films, allowing opposite modifications of the electron and hole density in the CuO$_2$ planes, an original situation with respect to conventional chemical doping in electron-doped materials. When the Hall effect indicates a large contribution of a hole band, the electric--field effect on the normal state resistivity is however dominated by the electrons, and the superconducting transition temperature increases when carriers are transfered from holes to electrons.
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