Signatures of superconducting and pseudogap phases in ultrafast transient reflectivity of Ca(Fe0.927Co0.073)2As2

Sunil Kumar; L. Harnagea; S. Wurmehl; B. Buechner; A. K. Sood

doi:10.1209/0295-5075/105/47004

All issues

Volume 105 / No 4 (February 2014)

EPL, 105 4 (2014) 47004

Abstract

Issue		EPL Volume 105, Number 4, February 2014


Article Number		47004
Number of page(s)		6
Section		Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
DOI		https://doi.org/10.1209/0295-5075/105/47004
Published online		03 March 2014

EPL, 105 (2014) 47004

Signatures of superconducting and pseudogap phases in ultrafast transient reflectivity of Ca(Fe_0.927Co_0.073)₂As₂

Sunil Kumar¹, L. Harnagea², S. Wurmehl², B. Buechner² and A. K. Sood¹^(b)

¹ Department of Physics, Indian Institute of Science - Bangalore 560012, India
² Leibniz-Institute for Solid State and materials Research, Dresden - D-01171 Dresden, Germany

^(b) asood@physics.iisc.ernet.in

Received: 13 September 2013
Accepted: 7 February 2014

Abstract

We present femtosecond time-resolved pump-probe spectroscopic studies of a pseudogap (PG) along with the superconducting (SC) gap in an overdoped iron pnictide Ca(Fe_0.927Co_0.073)₂As₂. It is seen that the temperature evolution of the photo-excited quasiparticle (QP) relaxation dynamics, coherently excited A_1g-symmetric optical phonon and two acoustic phonon dynamics behave anomalously in the vicinity of the superconducting transition temperature $T_{\text{c}}$ . A continuous change in the sign of the experimentally measured transient differential reflectivity $\Delta R/R$ signal at the zero time delay between the pump and probe pulses at a temperature of ${\sim}200\ \text{K}$ is inferred as an evidence of the emergence of the PG phase around that temperature. This behavior is independent of the pump photon energy and occurs for crystals without the spin density wave phase transition.

PACS: 78.47.J- – Ultrafast spectroscopy (<1 psec) / 74.70.Xa – Pnictides and chalcogenides / 74.25.Kc – Phonons

© EPLA, 2014

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