Observation Of Strain Wave In The Nematic Phase Of The Iron Pnictide Ba(Fe1-xCux)2As2 Using Dark-Field X-Ray Microscopy

Kaan Alp Yay^1,2, Elliot Kisiel^4,5, Matthew J. Krogstad⁴, Doga Gursoy⁴, Stephan O. Hruszkewycz⁴, Zahir Islam⁴, Ian R. Fisher<sup>1,3

1</sup>Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305
²Department of Physics, Stanford University, Stanford, CA 94305
³Department of Applied Physics, Stanford University, Stanford, CA 94305
⁴Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439
⁵Department of Physics, University of California San Diego, La Jolla, CA 92093

To gain a better understanding of the nematic phase in iron pnictides, we study underdoped Ba(Fe1-xCux)2As2 (Cu-Ba122) using dark-field X-ray microscopy (DFXM). DFXM is a novel technique which enables one to image the real-space distribution of a selected diffraction peak emanating from a domain within the bulk of a sample. Cu-Ba122 undergoes a tetragonal-to-orthorhombic structural phase transition at low temperature due to electronic nematicity, at which point orthorhombic twin domains form along the ab-plane. By imaging a single domain, we observed (1) micron-scale periodic spatial modulations of diffraction intensity and strain within a domain, and (2) an increase in the amplitude and period of the spatial modulations as temperature is lowered.

These observations demonstrate the existence of a mesoscopic strain wave within the orthorhombic phase of iron pnictides that has so far been undetected in traditional X-ray diffraction due to its long wavelength. Our results also establish DFXM as a powerful new tool to probe the mesoscopic behavior of strongly-correlated quantum materials.

Work at Stanford was supported by the Department of Energy, Office of Basic Energy Sciences, under contract DE-AC02-76SF00515. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

If you would like to meet with Kaan during his visit, please contact Susan LaMoreaux.