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Abstract
Thin films of the high-temperature superconductor HgBa2CaCu2O6 have been prepared on SrTiO3 substrates by pulsed-laser deposition of precursor films and subsequent annealing in mercury-vapor atmosphere. The microstructural properties of such films can vary considerably and have been analyzed by x-ray analysis and atomic force microscopy. Whereas the resistivity is significantly enhanced in samples with coarse-grained structure, the Hall effect shows little variation. This disparity is discussed based on models for transport properties in granular materials. We find that, despite of the morphological variation, all samples have similar superconducting properties. The critical temperatures T c ∼ 121.2 K …122.0 K, resistivity, and Hall data indicate that the samples are optimally doped. The analyses of superconducting order parameter fluctuations in zero and finite magnetic fields yield the in-plane ξ ab (0) ∼ 2.3 nm …2.8 nm and out-of-plane ξ c (0) ∼ 0.17 nm …0.24 nm Ginzburg–Landau coherence lengths at zero temperature. Hall measurements provide estimates of carrier scattering defects in the normal state and vortex pinning properties in the superconducting state inside the grains.
Highlights
The mercury cuprates of the Hg–Ba–Ca–Cu–O family form a homologous series with the chemical formula HgBa2Can − 1CunO2n+2+δ (HBCCO)
They show a linear behavior of the normal state resistivity ρxx, typical for optimally-doped cuprate HTSCs and a reduction of ρxx below the linear trend above Tc stemming from superconducting fluctuations [23]
We have investigated the resistivity and the Hall effect in three Hg-1212 thin films of different morphologies, which were characterized by x-ray diffraction and atomic force microscopy (AFM) scans
Summary
The mercury cuprates of the Hg–Ba–Ca–Cu–O family form a homologous series with the chemical formula HgBa2Can − 1CunO2n+2+δ (HBCCO). High-temperature superconductivity in the n = 1 compound [1] and the even higher transition temperatures Tc = 120 K in the n = 2 [2] and Tc = 135 K in the n = 3 material [3], respectively, has triggered enormous research interest. Mercury cuprates have been synthesized from n = 1 to 7 with Tc raising with the number n of neighboring CuO2 layers up to a maximum at n = 3 and decreasing for n > 3 [5] In contrast to their very promising superconducting properties, the mercury cuprates are hard to synthesize and handle due to the highly volatile and toxic nature of Hg and Hgbased compounds. Later it was demonstrated that HBCCO thin films can be grown on vicinal substrates in a well-oriented manner and form a roof-tile like structure that allows for measurements of in-plane and out-of-plane properties on the very same sample [10, 11]
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