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Temperature range of superconducting fluctuations above Tc in YBa2Cu3O7-d single crystals

Microwave absorption measurements in magnetic fields from zero up to 16T were used to determine the temperature range of superconducting fluctuations above the superconducting critical temperature Tc in YBa2Cu3O7−d. Measurements were performed on deeply underdoped, slightly underdoped, and overdoped single crystals. The temperature range of the superconducting fluctuations above Tc is determined by an experimental method which is free from arbitrary assumptions about subtracting the nonsuperconducting contributions to the total measured signal, and/or theoretical models to extract the unknown parameters. The superconducting fluctuations are detected in the ab−plane, and c−axis conductivity, by identifying the onset temperature T′. Within the sensitivity of the method, this fluctuation regime is found only within a fairly narrow region above Tc. Its width increases from 7K in the overdoped sample(Tc=89K), to at most 23K in the deeply underdoped sample(Tc=57K), so that T′ falls well below the pseudogap temperature T∗. Implications of these findings are discussed in the context of other experimental probes of superconducting fluctuations in the cuprates.

cuprate superconductors; response to electromagnetic fields; fluctuation phenomena; superconductivity phase diagrams

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