Reversible magnetization and critical fluctuations in systematically doped YBa${}_2$Cu${}_3$O${}_{7-\hat{I}´}$ single crystals

Abstract

The temperature and field dependence of reversible magnetization have been measured on a YBa${}_2$Cu${}_3$O${}_{7-\hat{I}´}$ single crystal at six different doping concentrations. It is found that the data above 2 T can be described by the scaling law based on the GL-LLL (lowest Landau level approach based on Ginzburg-Landau theory) critical fluctuation theory yielding the values of the slope of upper critical field $-\mathrm{d}{H}_{c2}(T)/\mathrm{d}T$ near $T_{\mathrm{c}}$. This set of values is self-consistent with that obtained in doing the universal scaling for the six samples. Based on a simple Ginzburg-Landau approach, we determined the doping dependence of the coherence length $\hat{I}¾$ which behaves in a similar way as that determined from $\hat{I}¾=\hslash v_{\mathrm{F}}/E_{\mathrm{sc}}$ with $E_{\mathrm{sc}}$ the superconducting energy scale. Our results may suggest a growing coherence length towards more underdoping.

4 pages, 4 figures