Imaging Anomalous Nematic Order and Strain in Optimally Doped BaFe_{2}(As,P)_{2}

Eric Thewalt; Ian M Hayes; James P Hinton; Arielle Little; Shreyas Patankar; Liang Wu; Toni Helm; Camelia V Stan; Nobumichi Tamura; James G Analytis; Joseph Orenstein

doi:10.1103/PhysRevLett.121.027001

Imaging Anomalous Nematic Order and Strain in Optimally Doped BaFe_{2}(As,P)_{2}

Phys Rev Lett. 2018 Jul 13;121(2):027001. doi: 10.1103/PhysRevLett.121.027001.

Authors

Eric Thewalt^{1

2}, Ian M Hayes^{1

2}, James P Hinton^{1

2}, Arielle Little^{1

2}, Shreyas Patankar^{1

2}, Liang Wu^{1

2}, Toni Helm^{1

2}, Camelia V Stan³, Nobumichi Tamura³, James G Analytis^{1

2}, Joseph Orenstein^{1

2}

Affiliations

¹ Department of Physics, University of California, Berkeley, California 94720, USA.
² Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
³ Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.

PMID: 30085755
DOI: 10.1103/PhysRevLett.121.027001

Abstract

We present the strain and temperature dependence of an anomalous nematic phase in optimally doped BaFe_{2}(As,P)_{2}. Polarized ultrafast optical measurements reveal broken fourfold rotational symmetry in a temperature range above T_{c} in which bulk probes do not detect a phase transition. Using ultrafast microscopy, we find that the magnitude and sign of this nematicity vary on a 50-100 μm length scale, and the temperature at which it onsets ranges from 40 K near a domain boundary to 60 K deep within a domain. Scanning Laue microdiffraction maps of local strain at room temperature indicate that the nematic order appears most strongly in regions of weak, isotropic strain. These results indicate that nematic order arises in a genuine phase transition rather than by enhancement of local anisotropy by a strong nematic susceptibility. We interpret our results in the context of a proposed surface nematic phase.