Simultaneous AC Susceptibility and Transport Current Study of the Intermediate Mixed State

AC magnetic susceptibility is a versatile probe ideally suited to study the various states of superconducting vortex matter [1]. We have recently developed an in-situ AC susceptibility and transport measurement setup that allows for parallel neutron scattering measurements. We used this setup to study the transport and self-organization phenomena in the intermediate mixed state (IMS) in Niobium, where flux-free Meissner state domains and domains filled with vortices, called mixed state domains coexist.

Vortices in a superconductor can be depinned using a transport current resulting in the flux flow state: For currents higher than the depinning current I_c vortices move orthogonal to the direction of the applied current resulting in an interesting scenario in the IMS due to its highly heterogeneous domain structure. Recent transport measurements [1] combined with small-angle neutron scattering showed a clear change from isotropic to anisotropic scattering, indicating, that the IMS rearranges itself into a stripe superstructure in the flux flow regime.

We used our custom-built AC susceptibility setup to further elucidate the re-organisation mechanism of the IMS: We present results from our recent simultaneous AC susceptibility and transport measurement study. As a main result we find a clear change in the Ic-B-curve when entering the IMS.

[1] C V Topping and S J Blundell 2019 J. Phys.: Condens. Matter 31 013001

[2] Xaver S Brems et al 2022 Supercond. Sci. Technol. 35 035003