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Superconducting fluctuations (SF) in SmFeAsO$_{0.8}$F$_{0.2}$ (characterized by superconducting transition temperature $T_{c} simeq 52.3$ K) are investigated by means of isothermal high-resolution dc magnetization measurements. The diamagnetic response to magnetic fields up to 1 T above $T_{c}$ is similar to what previously reported for underdoped cuprate superconductors and it can be justified in terms of metastable superconducting islands at non-zero order parameter lacking of long-range coherence because of strong phase fluctuations. In the high-field regime ($H gtrsim 1.5$ T) scaling arguments predicted on the basis of the Ginzburg-Landau theory of conventional SF are found to be applicable, at variance with what observed in the low-field regime. This fact enlightens that two different phenomena are simultaneously present in the fluctuating diamagnetism, namely the phase SF of novel character and the conventional SF. High magnetic fields (1.5 T $lesssim H ll H_{c2}$) are found to suppress the former while leaving unaltered the latter one.
To probe manifestations of multiband superconductivity in oxypnictides, we measured the angular dependence of magnetic torque $tau(theta)$ in the mixed state of SmO$_{0.8}$F$_{0.2}$FeAs single crystals as functions of temperature $T$ and high magneti
In this brief report an attempt is made for a mise-a-point of the subject of the phase fluctuations of the superconducting order parameter above Tc in cuprates, particularly as they appear in underdoped compounds. Measurements of torque magnetometry,
The low-temperature antiferromagnetic state of the Sm-ions in both nonsuperconducting SmFeAsO and superconducting SmFeAsO$_{0.9}$F$_{0.1}$ single crystals was studied by magnetic torque, magnetization, and magnetoresistance measurements in magnetic f
High resolution SQUID magnetization measurements in lead nanoparticles are used to study the fluctuating diamagnetism in zero-dimensional condition, namely for particle size d lesser than the coherence length. The diamagnetic magnetization Mdia (H, T
We present uSR investigations on SmFeAsO_1-xF_x showing coexistence of magnetic order and superconductivity only in a very narrow F-doping range. The sharp crossover between the two types of order is similar to that observed in LaFeAsO_1-xF_x, sugges