Observation of Local Pairs through Nonequilibrium Terahertz Spectroscopy in YBa2Cu3O7-{\delta} Below Tc

TL;DR

This study uses nonequilibrium terahertz spectroscopy to reveal local pairs coexisting with superconducting pairs in YBa2Cu3O7-δ, providing insights into the complex pairing mechanisms in high-temperature superconductors.

Contribution

It demonstrates the existence of local pairs without superconductivity coexisting with Cooper pairs using transient terahertz spectroscopy in cuprate superconductors.

Findings

Evidence of local pairs coexisting with superconducting pairs.

Temperature-dependent recovery time shows divergence below T_c.

Local pairs resemble short-range pair-density-wave states.

Abstract

Pairing states are essential to understanding the underlying mechanisms of high-temperature superconductivity. Here the non-superconducting state in an optimally doped YBa_2 Cu_3 O_(7-{\delta}) film was driven out of equilibrium by an optical pump with low fluence at a temperature well below the critical temperature (T_c), and its recovery dynamics were exclusively measured using transient terahertz spectroscopy. The pump-fluence dependent experiments unveiled evidence of local pairs without superconductivity coexisting with the superconducting Cooper pairs. An energy gap opening induced by the local pairing with short-range coherence was invoked to rationalize the temperature-dependent recovery time of local pairs with a characteristic divergence at a temperature substantially below T_c. These local pairs displayed remarkable likeness to the short-range pair-density-wave state. Our finding sheds light on understanding the dynamic interplay between the coexisting superconducting and non-superconducting pairs in cuprate superconductors.