3D visualizations of nano-scale phase separation and ultrafast dynamic correlation between phases in (Na0.32K0.68)0.95Fe1.75Se2

TL;DR

This study visualizes nano-scale phase separation and ultrafast phase dynamics in (Na0.32K0.68)0.95Fe1.75Se2, revealing key temperature-dependent interactions that shed light on the pairing mechanism in these superconductors.

Contribution

It presents the first 3D visualization of nano-scale phase separation and ultrafast dynamics in this material, linking phase interactions to superconductivity.

Findings

Nano-scale phase separation is fully percolative in 3D.

Two characteristic temperatures T* and TH mark phase coupling and metallic interface onset.

Energy transfer between phases suggests a new pairing mechanism insight.

Abstract

Phase separation of metallic and antiferromagnetic (AFM) insulating phases in alkaline iron selenides (AxFe2-ySe2) continues to attract intense interest because the relationship between two peculiar features probably is a key to clarifying the pairing mechanism of AxFe2-ySe2 superconductors. Here we report that the 3D visualizations of nano-scale phase separation in (Na0.32K0.68)0.95Fe1.75Se2 single crystals are revealed by hybrid focused-ion-beam scanning electron microscopy and the superconducting paths are fully percolative in 3D. Moreover, the phase-related ultrafast dynamics in (Na0.32K0.68)0.95Fe1.75Se2 is studied by dual-color pump-probe spectroscopy. The anomalous changes in the electron and acoustic phonon components of transient reflectivity change ({\Delta}R/R) identify two characteristic temperatures T*~100 K (the onset temperature of coupling between nano-metallic and AFM phases) and TH~230 K (the onset temperature of metallic-interface-phase). An energy-transfer channel between the nano-metallic and AFM phases is inferred. This proposed channel provides a new insight into the pairing mechanism of alkaline iron selenide superconductors.