Employing inelastic X-ray scattering and neutron scattering techniques, we observed nematic and magnetic phase transitions with distinct characters in K5Fe4Ag6Te10. Upon cooling, the nematic order undergoes a strongly first-order phase transition followed by a second-order magnetic transition at TN≈ 34.6 K. The temperature difference between these two phase transitions is ∼ 1 K. The observed phenomenon can be attributed to a distinctive first-order preemptive Ising-nematic transition, a characteristic unique to a quasi-two-dimensional scenario marked by strong out-of-plane spatial anisotropy due to weak coupling. Our studies establish K5Fe4Ag6Te10 as the first material in the family of iron pnictides and chalcogenides that possesses a nematic tricritical point preceding the magnetic one upon decreasing nematic coupling.
@article{arxiv.2407.14706,
title = {First Order Preemptive Ising-nematic Transition in K$_{5}$Fe$_{4}$Ag$_{6}$Te$_{10}$},
author = {N. Giles-Donovan and Y. Chen and H. Fukui and T. Manjo and D. Ishikawa and A. Q. R. Baron and S. Chi and H. Zhong and S. Cao and Y. Tang and Y. Wang and X. Lu and Y. Song and R. J. Birgeneau},
journal= {arXiv preprint arXiv:2407.14706},
year = {2024}
}