Campus Units

Physics and Astronomy, Ames Laboratory

Document Type

Article

Publication Version

Published Version

Publication Date

4-15-2017

Journal or Book Title

Physical Review B

Volume

95

Issue

16

First Page

165122

DOI

10.1103/PhysRevB.95.165122

Abstract

The origin of the anisotropic, paramagnetic phase associated with electronic nematicity in the iron pnictides is yet to be resolved. Furthermore, the detwinning technique used to study the nematic order in single crystals is known to introduce extra anisotropy into the sample, which can smear out the transition and even modify intrinsic characteristics associated with “spontaneous” Ising, Z2, symmetry breaking. Here we use a strain- and stress-free twinned sample to show that there is a significant reduction in the energy relaxation times of the hot electrons following nonequilibrium femtosecond laser excitation on both the high- and low-temperature sides of the nematic phase transition. This femtosecond critical speeding-up behavior provides an alternative way to study complex, electronically driven nematicity, neither invoking external strain nor measuring a small anisotropy in twinned crystals. Particularly, a detailed analysis of the observed ultrafast decay time and the amplitude associated with an initial electronic relaxation provides compelling implications on the physical origin of nematicity in iron pnictides: (1) nematic fluctuations strongly influence the dynamics of electron cooling, and (2) spin fluctuations determine the part of amplitude arising from the nematicity. Finally, we discuss ultrafast coherent phonon generation which may contribute to the measured transition temperature in our ultrafast measurements.

Comments

This article is published as Patz, A., T. Li, L. Luo, X. Yang, S. Bud'ko, P. C. Canfield, I. E. Perakis, and J. Wang. "Critical speeding up of nonequilibrium electronic relaxation near nematic phase transition in unstrained Ba (Fe 1− x Co x) 2 As 2." Physical Review B 95, no. 16 (2017): 165122. DOI: 10.1103/PhysRevB.95.165122. Posted with permission.

Copyright Owner

American Physical Society

Language

en

File Format

application/pdf

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