The Role of the Relaxation Rate of Nematic Fluctuations in the Tetragonal-to-Orthorhombic Transition in Fe Pnictides: a Raman Scattering Study

ORAL

Abstract

Raman scattering experiments were performed on LaFeAsO and Sr(Fe0.8Co0.2)2As2 crystals with well separated antiferromagnetic (TAF) and tetragonal-orthorhombic (Tt-o) transitions (Tt-o - TAF ~ 15-20 K). In both cases, a quasi-elastic peak (QEP) was observed in B2g symmetry (2 Fe cell) that fades away below ~TAF and is ascribed to nematic fluctuations. The QEP width is continuously reduced down to TAF, indicating longer relaxation times of nematic fluctuations on cooling. The onset of the structural transition in both compounds coincides with the temperature where the QEP width reaches a threshold value of ~ 40 cm-1. Also, the QEP widths at T >~ TAF are significantly smaller than the reported value at comparable temperatures for BaFe2As2 with much smaller Tt-o - TAF separation. Based on these results, we propose that the structural phase transition in pnictides is preempted by a slowing of the electronic nematic fluctuations down to a phonon-defined timescale where the nuclei positions can respond to such fluctuations and be readily locked into the orthorhombic phase.

*Supported by FAPESP and CNPq, Brazil, and DOE Basic Energy Sciences, Contract #DE-AC02-07CH11358, USA.

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Presenters

  • Eduardo Granado

    • Institute of Physics "Gleb Wataghin", University of Campinas - UNICAMP

Authors

  • Ulisses Kaneko

    • Institute of Physics "Gleb Wataghin", University of Campinas - UNICAMP

  • Mário Piva

    • Institute of Physics "Gleb Wataghin", University of Campinas - UNICAMP

  • Paulo Gomes

    • Institute of Physics "Gleb Wataghin", University of Campinas - UNICAMP

  • Alí García-Flores

    • Universidade Federal do ABC

  • Jiaqiang Yan

    • Materials Science and Technology Division, Oak Ridge National Laboratory
    • Oak Ridge National Lab
    • Oak Ridge National Laboratory
    • Ames Laboratory, Iowa State University

  • T. A. Lograsso

    • Ames Laboratory and Department of Physics & Astronomy, Iowa State University
    • Ames Laboratory
    • Ames Laboratory, Iowa State University

  • Gaston Barberis

    • Institute of Physics "Gleb Wataghin", University of Campinas - UNICAMP

  • Pascoal Pagliuso

    • Institute of Physics "Gleb Wataghin", University of Campinas - UNICAMP

  • David Vaknin

    • Ames Laboratory, Iowa State University

  • Eduardo Granado

    • Institute of Physics "Gleb Wataghin", University of Campinas - UNICAMP