Evidence of anisotropic phase correlations above Tc in single crystalline Ba0.54K0.46Fe2As2

Isofield magnetization curves have been recorded and analyzed in optimally doped Ba1−xKxFe2As2 single crystal in two main crystallographic directions (H||c-axis and H||ab-planes). Near transition temperature (T)c, magnetization exhibits temperature dependence −M∝[Ta(H)−T]m, where Ta is the apparent transition temperature and represents onset of phase coherence of the superconducting order parameter. We have shown that Ta behaves differently in two main crystallographic directions: dTa(H)/dH>0 for H||ab-planes and dT(H)a/dH<0 for H||c-axis. In H||ab-planes we have observed Ta(H)>Tc which implies that magnetic field can probe a region above Tc where phase correlation persists. We suggest that multiband character may be the possible reasons for anomalous behavior of Ta. The obtained values of fitting exponents (m) are larger than 0.5 and increase with magnetic field.