Detection of the flux dynamical regimes in Bi4O4S3 by multiharmonic AC susceptibility

• The first harmonic of the AC magnetic susceptibility reveals a bulk superconductivity.
• Both the first and the third harmonics of the AC magnetic susceptibility exhibit a nonlinear behaviour.
• The third harmonic confirms the existence of a critical state together with flux creep regime and non linear flux flow.
• The quantitative analysis of the activation energy and the critical current density confirm the presence of creep.

The temperature dependent first and third harmonics of the AC magnetic susceptibility χ1,3(T) have been measured on Bi4O4S3. The χ1(T) magnetic response is due to the intergranular contribution with a transition temperature Tc ≈ 4.4 K. The dependencies of the χ3(T) on the AC field amplitude and frequency reveal a critical state with the presence of the flux creep and the flux flow regimes. In fact, the field dependencies of the effective activation energy and of the frequency dependent critical current density have been found to be described with power laws characteristic of the collective creep regime involving large flux bundles.