Fluctuation spectroscopy of disordered two-dimensional superconductors

We revise the long-studied problem of fluctuation conductivity (FC) in disordered two-dimensional superconductors placed in a perpendicular magnetic field by finally deriving the complete solution in the temperature-magnetic field phase diagram. The obtained expressions allow both to perform straightforward (numerical) calculation of the FC surface δσₓₓ⁽ᵗᵒᵗ⁾(T,H) and to get asymptotic expressions in all its qualitatively different domains. This surface becomes in particular nontrivial at low temperatures, where it is trough-shaped with δσₓₓ⁽ᵗᵒᵗ⁾(T,H)<0. In this region, close to the quantum-phase transition, δσₓₓ⁽ᵗᵒᵗ⁾(T,H=const) is nonmonotonic, in agreement with experimental findings. We reanalyzed and present comparisons to several experimental measurements. Based on our results we derive a qualitative picture of superconducting fluctuations close to Hc2(0) and $T=0$ where fluctuation Cooper pairs rotate with cyclotron frequency ωc~ΔBCS^-1 and Larmor radius ~{{ξ}}BCS$, forming some kind of quantum liquid with long coherence length ${{ξ}}QF{}{{ξ}}BCS$ and slow relaxation (${{τ}}QF{}{}{{Δ}}BCS^{{-}1}$).