Fluctuoscopy 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 $δσ_{xx}^{(\mathrm{tot})}(T,H)$ and to get asymptotic expressions in all its qualitatively different domains. This surface becomes in particular non-trivial at low temperatures, where it is trough-shaped with $% δσ_{xx}^{(\mathrm{tot})}(T,H)<0$. In this region, close to the quantum phase transition, $δσ_{xx}^{(\mathrm{tot})}(T,H=\mathrm{const})$ is non-monotonic, 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 $H_{\mathrm{c2}}(0) $ and T=0 where fluctuation Cooper pairs rotate with cyclotron frequency $ω_{c}\simΔ_{\mathrm{BCS}}^{-1}$ and Larmor radius $\sim ξ_{\mathrm{BCS}}$, forming some kind of quantum liquid with long coherence length $ξ_{\mathrm{QF}}\ggξ_{\mathrm{BCS}}$ and slow relaxation ($τ_{\mathrm{QF}}\gg\hbarΔ_{\mathrm{BCS}}^{-1}$).