Fluctuation spectroscopy of iron-based superconductors Ba(Fe 1– x Co x ) 2 As 2

Abstract Nematicity and its influence on the superconducting phase in Ba(Fe 1−x Co x ) 2 As 2 is still a major research interest as the origin of unconventional superconductivity in iron pnictides is still under debate. One of the remaining questions is how the magnetic and structural transitions, with nematic fluctuations extending over a wide temperature range, influence the charge carrier dynamics in particular at low frequencies. We present resistance fluctuation measurements on high-quality Ba(Fe 1− x Co x ) 2 As 2 samples, made possible by cutting a meander structure into the sample by means of a focused ion beam. The preparation process is described and the resulting temperature-dependent noise properties of three different substitution levels ( x = 0 %, x = 4 % and x = 6 %) are presented. We observe only small changes in the noise amplitude in the vicinity of the nematic transition temperatures. However, a larger feature in the ordered phase of the x = 4 % doped sample is detected, which may be related to a strong coupling of the charge carriers to lattice modes at domain walls. Future work on straining and detwinning the samples, as well as an anisotropy analysis of the fluctuations on one and the same sample, may allow to clarify the results.