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Low frequency response of superconducting fluctuations in La2-xSrxCuO4

The superconducting fluctuation regime in the pseudogap phase of cuprate superconductors has been under extensive investigation for many years. By measuring microwave conductivity (~15 GHz), we have shown that the fluctuation regime of compounds (HgBa2CuO4+δ and YBa2Cu3O6+δ) with high maximal transition temperatures at optimal doping (Tcmax ≈ 93-97 K) is confined to a narrow temperature range, extending just 10-15 K above Tc [1-2]. Recently, THz time-domain spectroscopy (0.2-1.5 THz) on thin films of the low-Tc max compound La2-xSrxCuO4 (Tcmax ≈ 40 K) [3] indicated the presence of fast superconducting fluctuations in a similarly narrow temperature range (10-15 K above Tc). In order to clarify whether the observation of a narrow fluctuation regime is a universal property of the cuprates and not limited to specific compounds or probes, we have studied the microwave conductivity of high-quality, single crystals of La2-xSrxCuO4 and determined the ac conductivity parallel (σab) and perpendicular (σc) to the CuO2 planes. By applying an external magnetic field, we were able to extract the contribution due to superconducting fluctuations. Consistent with the aforementioned studies, the fluctuation regime in bulk single crystals of this low-Tcmax compound is narrow and tracks the superconducting dome. Acknowledgement/Reference: [1] M. S. Grbić et al., Phys. Rev. 80, 094511 (2009). [2] M. S. Grbić et. al., Phys. Rev. B 83, 144508 (2011). [3] L. S. Bilbro, R. Valdés Aguilar, G. Logvenov, O. Pelleg, I. Božović, N. P. Armitage, Nat. Phys. 7, 298 (2011).

superconductivity; fluctuations; cuprates; ac conductivity

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