Ultrafast dynamics of quasiparticles and coherent acoustic phonons in slightly underdoped (BaK)Fe2As2

Kung-Hsuan Lin,Chung-Chieh Chang,Ching-Wu Chu,Yu-Chieh Wen,Maw-Kuen Wu,Bing Lv,Kuan-Jen Wang

doi:10.1038/srep25962

Abstract

We have utilized ultrafast optical spectroscopy to study carrier dynamics in slightly underdoped (BaK)Fe2As2 crystals without magnetic transition. The photoelastic signals due to coherent acoustic phonons have been quantitatively investigated. According to our temperature-dependent results, we found that the relaxation component of superconducting quasiparticles persisted from the superconducting state up to at least 70 K in the normal state. Our findings suggest that the pseudogaplike feature in the normal state is possibly the precursor of superconductivity. We also highlight that the pseudogap feature of K-doped BaFe2As2 is different from that of other iron-based superconductors, including Co-doped or P-doped BaFe2As2.

Highlights

We have utilized ultrafast optical spectroscopy to study carrier dynamics in slightly underdoped (BaK) Fe2As2 crystals without magnetic transition
Compounds of the 122 system are the easiest among the iron-based superconductors to synthesize in the form of large single crystals, and most publications have been devoted to 122 compounds[2]
Ultrafast optical spectroscopy[24,25,26,27,28,29,30] is not surface-sensitive, and is a convenient tool to study the bulk property of materials

Summary

Introduction

We have utilized ultrafast optical spectroscopy to study carrier dynamics in slightly underdoped (BaK) Fe2As2 crystals without magnetic transition. We highlight that the pseudogap feature of K-doped BaFe2As2 is different from that of other iron-based superconductors, including Codoped or P-doped BaFe2As2. It should be noted that its parent compound, BaFe2As2, has a structural and magnetic phase transition[19], but Ba1−xKxFe2As2 is only superconducting (SC) for a range of x with maximum Tc at x = 0.420. There are contradictory results about the existence of pseudogap in optimally doped (BaK)Fe2As2 (BKFA) from angle-resolved photoemission spectroscopy (ARPES) measurements[22,23]. By observing the temperature-dependent quasiparticle-relaxation, a pseudogaplike feature has been observed in FeSe25, LiFeAs26, Ba(Fe,Co)2As2 27, Ca(Fe,Co)2As2 28, SmFeAsO0.8F0.2 29, and underdoped BKFA30. We found that the quasiparticle relaxation associated with the SC gap has temperature dependence www.nature.com/scientificreports/

Methods

Results

Conclusion