We calculate superfluid density for a dirty d-wave superconductor. The effects of impurity scattering are treated within the self-consistent t-matrix approximation, in weak-coupling BCS theory. Working from a realistic tight-binding parameterization of the Fermi surface, we find a superfluid density that is both correlated with Tc and linear in temperature, in good correspondence with recent experiments on overdoped La2−xSrxCuO4.

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SrTiO_{3} exhibits a superconducting dome upon doping with Nb, with a maximum critical temperature T_{c}≈0.4  K. Using microwave stripline resonators at frequencies from 2 to 23 GHz and temperatures down to 0.02 K, we probe the low-energy optical response of superconducting SrTiO_{3} with a charge carrier concentration from 0.3 to 2.2×10^{20}  cm^{-3}, covering the majority of the superconducting dome. We find single-gap electrodynamics even though several electronic bands are superconducting. This is explained by a single energy gap 2Δ due to gap homogenization over the Fermi surface consistent with the low level of defect scattering in Nb-doped SrTiO_{3}. Furthermore, we determine T_{c}, 2Δ, and the superfluid density as a function of charge carrier concentration, and all three quantities exhibit the characteristic dome shape.

A topological insulator is a state of matter which does not break any symmetry and is characterized by topological invariants, the integer expectation values of nonlocal operators. Antiferromagnetism, on the other hand, is a broken symmetry state in which the translation symmetry is reduced and time reversal symmetry is broken. Can these two phenomena coexist in the same material? A proposal by Mong et al. [Phys. Rev. B 81, 245209 (2010)] asserts that the answer is yes. Moreover, it is theoretically possible that the onset of antiferromagnetism enables the nontrivial topology since it may create spin-orbit coupling effects which are absent in the nonmagnetic phase. The current work examines a real system, half-Heusler GdBiPt, as a candidate for topological antiferromagnetism. We find that the magnetic moments of the gadolinium atoms form ferromagnetic sheets which are stacked antiferromagnetically along the body diagonal. This magnetic structure may induce spin-orbit coupling on band electrons as they hop perpendicular to the ferromagnetic sheets.

FeSe is an iron-based superconductor of immense current interest due to the large enhancements of T c that occur when it is pressurised or grown as a single layer on an insulating substrate. Here we report precision measurements of its superconducting electrodynamics, at frequencies of 202 and 658 MHz and at temperatures down to 0.1 K. The quasiparticle conductivity reveals a rapid collapse in scattering on entering the superconducting state that is strongly reminiscent of unconventional superconductors such as cuprates, organics and the heavy fermion material CeCoIn 5 . At the lowest temperatures the quasiparticle mean free path exceeds 50 μm, a record for a compound superconductor. From the superfluid response we confirm the importance of multiband superconductivity and reveal strong evidence for a non-zero energy-gap minimum.