1107.0351 (Daisuke Nakamura et al.)

Superconducting Fluctuation investigated by THz Conductivity of
La$_{2-x}$Sr$_x$CuO$_4$ Thin Films    [PDF]

Daisuke Nakamura, Yoshinori Imai, Atsutaka Maeda, Ichiro Tsukada

Frequency-dependent terahertz conductivities of La$_{2-x}$Sr$_x$CuO$_4$ thin
films with various carrier concentrations were investigated. The imaginary part
of the complex conductivity considerably increased from far above a
zero-resistance superconducting transition temperature,
$T_\text{c}^\text{zero}$, because of the existence of the fluctuating
superfluid density with a short lifetime. The onset temperature of the
superconducting fluctuation is at most $\sim 2T_\text{c}^\text{zero}$ for
underdoped samples, which is consistent with the previously reported analysis
of microwave conductivity. The superconducting fluctuation was not enhanced
under a 0.5 T magnetic field. We also found that the temperature dependence of
the superconducting fluctuation was sensitive to the carrier concentration of
La$_{2-x}$Sr$_x$CuO$_4$, which reflects the difference in the nature of the
critical dynamics near the superconducting transition temperature. Our results
suggest that the onset temperature of the Nernst signal is not related to the
superconducting fluctuation we argued in this paper.

View original: http://arxiv.org/abs/1107.0351