Extended paraconductivity regime in underdoped cuprates

We reconsider transport experiments in strongly anisotropic high-$T_c$ superconducting cuprates and we find that the universal Aslamazov-Larkin paraconductivity in two dimensions is surprisingly robust, even in the underdoped regime below the pseudogap crossover temperature $T^{*}$. We also establish that the underlying normal-state resistivity in the pseudogap region is (almost) linear in temperature, with all the deviations being quantitatively accounted for by Aslamazov-Larkin paraconductivity. The disappearance of paraconductivity is ruled by the suppression of Gaussian pair fluctuations at an energy scale related to $T^{*}$.

Figure 1

(Color online) (a) Paraconductivity data, as obtained by taking the different normal-state resistivities. The resistivity data [black circles in Fig. 1b] are from Ref. 29 for a BSCCO sample at doping $x=0.217$. The symbols of each set of paraconductivity points corresponds to the symbols of the corresponding normal-state resistivity curves of Fig. 1b. The solid straight line is the universal two-dimensional AL paraconductivity, Eq. (3), with no adjustable parameter. (b) Resistivity data (black circles) and various hypothetical forms of the normal-state resistivity. All the curves coincide with a straight line above $T^{*}=250\mathrm{K}$, while are quadratic below it [see Eq. (8)]. The first curve from top has a positive curvature, $B>0$; the second, third, and fourth curve have a negative curvature, $B<0$, which increases in absolute value from top to bottom. The normal-state hypothetical curves are extended to the region below the critical temperature to make them more clearly distinguishable by emphasizing their separation.

Figure 2

(Color online) (a) Paraconductivity data, as obtained by taking the different normal-state resistivities. The resistivity data [black circles in Fig. 2b] are from Ref. 29 for a BSCCO sample at doping $x=0.22$. The symbols of each set of paraconductivity points corresponds to the symbols of the corresponding normal-state resistivity curves of Fig. 2b. The solid straight line is the universal two-dimensional AL paraconductivity, Eq. (3) with no adjustable parameter. (b) Resistivity data (black circles) and various hypothetical forms of the normal-state resistivity. All the curves coincide with a straight line above $T^{*}=220\mathrm{K}$, while are quadratic below it [see Eq. (8)]. The first curve from top has a positive curvature, $B>0$; the second, third, and fourth curve have a negative curvature, $B<0$, which increases in absolute value from top to bottom. The normal-state hypothetical curves are extended to the region below the critical temperature to make them more clearly distinguishable by emphasizing their separation.