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Ruslan Prozorov - Ames Laboratory and Department of Physics & Astronomy, Iowa State University, USA

Anisotropy of normal and superconducting state in Fe-based superconductors

Experimental determination of the anisotropy of the electromagnetic and thermodynamic response is crucially important for any superconductor. Electrical resistivity is sensitive to the details of the density of states and excitations in electronic, magnetic and lattice subsystems. London penetration depth and thermal conductivity, on the other hand, depend on the number of excited quasiparticles determined by the structure of the superconducting gap, thus providing valuable insight into the pairing mechanism. Furthermore, scattering plays an important role in determining experimentally observed behavior. Magnetic response in the mixed (vortex) state is also very sensitive to both pairing symmetry and defect structure of the material.


I will summarize our experimental results on the temperature-dependent anisotropic London penetration depth in single crystals of the ’’11’’, ’’111’’, ’’1111’’ and ’’122’’ families of Fe-based superconductors and compare them with thermal conductivity measurements. Next, I will discuss in-plane and c-axis resistivity in and possible nematic electronic ordering above the structural/magnetic transition. If time allows, I will also show some unusual behavior in the vortex state.


Non-Fermi liquid behavior, a substantial influence of magnetism, different gaps with doping-dependent three-dimensional anisotropy and pair-breaking scattering follow from the experimental observations. Overall, the results support s_+/- pairing that evolves from nodeless to nodal (with significant 3D character) upon departure from the optimal doping in Fe-based superconductors.


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