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Nonlinear and time-resolved optical study of the 112-type iron-based superconductor parent Ca_(1−x)La_xFeAs_2 across its structural phase transition

Harter, J. W. and Chu, H. and Jiang, S. and Ni, N. and Hsieh, D. (2016) Nonlinear and time-resolved optical study of the 112-type iron-based superconductor parent Ca_(1−x)La_xFeAs_2 across its structural phase transition. Physical Review B, 93 (10). Art. No. 104506. ISSN 1098-0121.

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The newly discovered 112-type ferropnictide superconductors contain chains of As atoms that break the tetragonal symmetry between the ɑ and b axes. This feature eliminates the need for uniaxial strain that is usually required to stabilize large single domains in the electronic nematic state that exists in the vicinity of magnetic order in the iron-based superconductors. We report detailed structural symmetry measurements of 112-type Ca_(0.73)La_(0.27)FeAs_2 using rotational anisotropy optical second-harmonic generation. This technique is complementary to diffraction experiments and enables a precise determination of the point-group symmetry of a crystal. By combining our measurements with density functional theory calculations, we uncover a strong optical second-harmonic response of bulk electric dipole origin from the Fe and Ca 3d-derived states that enables us to assign C_2 as the crystallographic point group. This makes the 112-type materials high-temperature superconductors without a center of inversion, allowing for the possible mixing of singlet and triplet Cooper pairs in the superconducting state. We also perform pump-probe transient reflectivity experiments that reveal a 4.6-THz phonon mode associated with the out-of-plane motion of As atoms in the FeAs layers. We do not observe any suppression of the optical second-harmonic response or shift in the phonon frequency upon cooling through the reported monoclinic-to-triclinic transition at 58 K. This allows us to identify C_1 as the low-temperature crystallographic point group but suggests that structural changes induced by long-range magnetic order are subtle and do not significantly affect electronic states near the Fermi level.

Item Type:Article
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URLURL TypeDescription
Harter, J. W.0000-0002-7146-9370
Chu, H.0000-0002-1989-9517
Hsieh, D.0000-0002-0812-955X
Additional Information:© 2016 American Physical Society. Received 9 December 2015; revised manuscript received 6 February 2016; published 7 March 2016. RA-SHG and transient reflectivity experiments were supported by the U. S. Department of Energy under Award No. DE-SC0010533. Instrumentation for the RA-SHG setup was partially supported by a U. S. Army Research Office DURIP award under Grant No. W911NF-13-1-0293 and the Alfred P. Sloan Foundation under Grant No. FG-BR2014-027. D.H. also acknowledges funding from the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center (PHY-1125565) with support of the Gordon and Betty Moore Foundation through Grant No. GBMF1250. Work at UCLA was supported by the U.S. Department of Energy Office of Basic Energy Sciences under Award No. DE-SC0011978.
Group:Institute for Quantum Information and Matter
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0010533
Army Research Office (ARO)W911NF-13-1-0293
Alfred P. Sloan FoundationFG-BR2014-027
Institute for Quantum Information and Matter (IQIM)UNSPECIFIED
Gordon and Betty Moore FoundationGBMF1250
Department of Energy (DOE)DE-SC0011978
Issue or Number:10
Record Number:CaltechAUTHORS:20160401-095101047
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Official Citation:Nonlinear and time-resolved optical study of the 112-type iron-based superconductor parent Ca1−xLaxFeAs2 across its structural phase transition J. W. Harter, H. Chu, S. Jiang, N. Ni, and D. Hsieh Phys. Rev. B 93, 104506 (2016) – Published 7 March 2016
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:65841
Deposited By: Ruth Sustaita
Deposited On:01 Apr 2016 19:24
Last Modified:04 Jun 2020 10:14

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