Temperature range of superconducting fluctuations above T_c in YBa_2Cu_3O_{7-\delta} single crystals

TL;DR

This study uses microwave absorption to precisely measure the temperature range of superconducting fluctuations above T_c in YBa_2Cu_3O_{7-eta} single crystals across different doping levels, revealing a narrow fluctuation regime below the pseudogap temperature.

Contribution

It introduces an experimental method that accurately determines the fluctuation regime without relying on theoretical models or arbitrary subtraction, highlighting the narrow fluctuation window in cuprates.

Findings

Fluctuation regime width increases from 7 K to 23 K with underdoping.

Superconducting fluctuations are confined within a narrow temperature range above T_c.

Fluctuation onset temperature T' is well below the pseudogap temperature T*.

Abstract

Microwave absorption measurements in magnetic fields from zero up to 16 T were used to determine the temperature range of superconducting fluctuations above the superconducting critical temperature T_c in YBa_2Cu_3O_{7-\delta}. Measurements were performed on deeply underdoped, slightly underdoped, and overdoped single crystals. The temperature range of the superconducting fluctuations above T_c 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 T_c. Its width increases from 7 K in the overdoped sample (T_c = 89 K), to at most 23 K in the deeply underdoped sample (T_c = 57 K), 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.