The role of nematic fluctuations in the pairing mechanism of iron-based superconductors is frequently debated. Here we present a novel method to reveal such fluctuations by identifying energy and momentum of the corresponding nematic boson through the detection of a boson-assisted resonant amplification of Friedel oscillations. Using Fourier-transform scanning tunneling spectroscopy, we observe for the unconventional superconductor LiFeAs strong signatures of bosonic states at momentum q∼0 and energy Ω≈8~meV. We show that these bosonic states survive in the normal conducting state, and, moreover, that they are in perfect agreement with well-known strong above-gap anomalies in the tunneling spectra. Attributing these small-q boson modes to nematic fluctuations we provide the first spectroscopic approach to the nematic boson in an unconventional superconductor.
@article{arxiv.1811.03489,
title = {Spectroscopic evidence of nematic fluctuations in LiFeAs},
author = {Zhixiang Sun and Pranab Kumar Nag and Steffen Sykora and Jose M. Guevara and Sven Hoffmann and Christian Salazar and Torben Hänke and Rhea Kappenberger and Sabine Wurmehl and Bernd Büchner and Christian Hess},
journal= {arXiv preprint arXiv:1811.03489},
year = {2019}
}