Abstract
Competing ferroelectric and charge density wave states have been proposed to exist in the electron-phonon coupled LaO1-xFxBiS2 superconductor. The lattice instability is proposed to arise from unstable phonon modes that can break the crystal symmetry. Using single crystal diffraction, a superlattice pattern is observed, that arises from coherent in-plane displacements of the sulfur atoms in the BiS2 superconducting planes. The distortions morph into coordinated ferrodistortive patterns with displacements in the x- and y-directions, that alternate along the c-axis. Diffuse scattering is observed along the (H0L) plane due to stacking faults but not along the (HH0) plane. The ferro-distortive pattern remains in the superconducting state upon fluorine doping, but the displacements are diminished in magnitude. Moreover, we find that the in-plane distortions give rise to disorder where the (00L) reflections become quite broad. It is possible that charge carriers can get trapped in the lattice deformations reducing the effective number of carriers available for pairing.
| Original language | English |
|---|---|
| Article number | 054701 |
| Journal | Journal of the Physical Society of Japan |
| Volume | 86 |
| Issue number | 5 |
| DOIs | |
| State | Published - May 15 2017 |
Funding
The authors would like to acknowledge support from the National Science Foundation, DMR-1404994, 1265162, and 1334170. Work at ORNL was supported by the US Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division and Scientific User Facilities Division. Work at the Advanced Photon Source, was supported by the US Department of Energy, Office of Science User Facility, and operated by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.