Paraconductivity of underdoped La2-x Srx Cu O4 thin-film superconductors using high magnetic fields

Abstract

The contribution of superconducting fluctuations to the conductivity, or paraconductivity, is studied in the underdoped regime of La2-x Srx Cu O4 cuprates. A perpendicular magnetic field up to 50 T is applied to suppress the superconductivity and obtain the normal state resistivity, which is then used to calculate the paraconductivity. Surprisingly enough, it is consistent with a two-dimensional Aslamazov-Larkin regime of Gaussian fluctuations close to the critical temperature. At higher temperature, the paraconductivity exhibits a power-law decrease in temperature (as T-α), as was previously shown for underdoped Y Ba2 Cu3 O7-δ and Bi2 Sr2 Ca Cu2 O8+δ samples. Our observations are not consistent with the existence of Kosterlitz-Thouless fluctuations. This tends to indicate that the superconducting pair amplitude is not already defined above TC in the pseudogap state. © 2007 The American Physical Society.