Microwave Signature of the Emerging Abrikosov Lattice above H_{c2}

The emergence of the Abrikosov lattice in the normal phase of type-II superconducting films as the magnetic field approaches the critical field H_{c2} from above was predicted in Glatz et al. [Fluctuation spectroscopy of disordered two-dimensional superconductors, Phys. Rev. B 84, 104510 (2011)PRBMDO1098-012110.1103/PhysRevB.84.104510]. In the quantum fluctuation regime [Galitski and Larkin, Superconducting fluctuations at low temperature, Phys. Rev. B 63, 174506 (2001)PRBMDO0163-182910.1103/PhysRevB.63.174506], it is characterized by the formation of relatively large (ξ_{QF}∼ξ_{BCS}/sqrt[h[over ˜]], h[over ˜]=H/H_{c2}-1) and long-lived (τ_{QF}∼τ_{Δ}/h[over ˜], τ_{Δ}=ℏ/Δ) clusters of rotating fluctuation Cooper pairs, representing precursors of Abrikosov vortices. We show that these fluctuation-induced vortex clusters can be detected through their high-frequency electromagnetic response. Specifically, they produce a pronounced enhancement of the imaginary part of the ac conductivity at characteristic frequencies ω_{QF}∼h[over ˜]/τ_{Δ}, arising directly from quantum fluctuations, being well below the superconducting threshold at 2/τ_{Δ}. For niobium, ω_{QF} falls within the experimentally accessible microwave range, making this effect directly testable using modern microwave spectroscopy.