Non-conventional superconducting fluctuations in Ba(Fe1-xRhx)2As2 iron-based superconductors

We measured the static uniform spin susceptibility of Ba(Fe(1-x)Rh(x))(2)As(2) iron-based superconductors, over a broad range of doping (0.041 ⩽ x ⩽ 0.094) and magnetic fields. At small fields (H ⩽ 1 kOe) we observed, above the transition temperature Tc, the occurrence of precursor diamagnetism, which is not ascribable to the Ginzburg-Landau theory. On the contrary, our data agree with a phase fluctuation model, which has been used to interpret a similar phenomenology occurring in the high-Tc cuprate superconductors. Additionally, in the presence of strong fields, the unconventional fluctuating diamagnetism is suppressed, whereas Ginzburg-Landau fluctuations are found, in agreement with literature.