Superconducting coherence lengths of hole-doped cuprates obtained from electron-boson spectral density functions

TL;DR

This study uses electron-boson spectral density functions derived from optical spectra to estimate superconducting coherence lengths in hole-doped cuprates, linking spin fluctuations to Cooper pair formation.

Contribution

It introduces a method to determine coherence lengths from EBSDFs, connecting microscopic spin fluctuation timescales to superconducting properties in cuprates.

Findings

Coherence lengths are consistent with other experimental measurements.

EBSDFs reveal spin fluctuation timescales relevant to pairing.

Superconductivity in cuprates is linked to spin fluctuation mechanisms.

Abstract

Electron-boson spectral density functions (EBSDFs) can be obtained from measured spectra using various spectroscopic techniques, including optical spectroscopy. EBSDFs, known as glue functions, have a magnetic origin. Here, we investigated EBSDFs obtained from the measured optical spectra of hole-doped cuprates with wide doping levels, from underdoped to overdoped cuprates. The average frequency of an EBSDF provides the timescale for the spin fluctuations to form Cooper pairs. This timescale is directly associated with retarded interactions between electrons. Using this timescale and Fermi velocity, a reasonable superconducting coherence length, which reflects the size of the Cooper pair, can be extracted. The obtained coherence lengths were consistent with those measured via other experimental techniques. Therefore, the formation of Cooper pairs in cuprates can be explained by spin fluctuations, the timescales of which appear in EBSDFs. Consequently, EBSDFs provide crucial information on the timescale of the microscopic mechanism of Cooper pair formation.