Low energy excitations inside the vortex core of LiFe(As, P) single crystals investigated by microwave-surface impedance

The flux-flow resistivity and the electronic state inside the vortex core in single crystals of LiFe(As, P) were investigated by microwave-surface impedance. The flux-flow resistivity of these materials increase linearly with the magnetic field, and it is consistent with an isotropic gap nature of materials. However, the gradient is larger than theoretical predictions for superconductors with isotropic gap structure. It is probably the consequence of multiple-bands nature of these materials. We also found that the materials have the moderately clean core, and the mean free path of the quasi-particle inside the vortex core is much shorter than that outside the core, and rather comparable to the core radius. We believe that this is a novel and a universal feature of all superconductors.

► We measure the microwave-surface impedance under finite magnetic fields.
► Both LiFeAs and LiFe(As, P) single crystals have the moderately clean core.
► The quasiparticle scattering time inside vortex cores is shorter than that outside.
► The flux-flow resistivity of LiFe(As, P) increases linearly with magnetic fields.
► The large gradient is probably the consequence of multiple-bands nature.