Ultrafast pump-probe study of phase separation and competing orders in the underdoped (Ba,K)Fe$_{2}$As$_{2}$ superconductor

TL;DR

This study uses ultrafast pump-probe techniques to investigate the dynamics of phase separation and competing orders, such as SDW and superconductivity, in underdoped (Ba,K)Fe$_{2}$As$_{2}$, revealing a normal-state order preceding superconductivity.

Contribution

It provides new insights into the quasiparticle relaxation dynamics and identifies a precursor normal-state order in underdoped iron-based superconductors.

Findings

Spin-density wave order forms at ~85 K.

Superconductivity emerges at ~28 K.

A normal-state order suppresses SDW at ~60 K.

Abstract

We report measurements of quasiparticle relaxation dynamics in the high-temperature superconductor (Ba,K)Fe$_{2}$As$_{2}$ in optimally doped, underdoped and undoped regimes. In the underdoped sample, spin-density wave (SDW) order forms at $\sim$85 K, followed by superconductivity at $\sim$ 28 K. We find the emergence of a normal-state order that suppresses SDW at a temperature $T^{\ast} \sim$ 60 K and argue that this normal-state order is a precursor to superconductivity.