Two-step phase transitions in Fe(Se,Te)

TL;DR

This study reveals a two-step structural phase transition in Fe(Se,Te) crystals, involving electronic reconstruction and subsequent structural change, with implications for understanding phase diagrams and quantum critical points in these materials.

Contribution

It uncovers the two-stage phase transition process in Fe(Se,Te) and links it to similar behavior under pressure in pure FeSe, suggesting a possible triple point near the quantum critical point.

Findings

Electronic subsystem undergoes reconstruction at high temperature.

Abrupt change in NMR relaxation rate during the transition.

Presence of a possible triple point near the quantum critical point.

Abstract

In the studied crystals of FeSe0.7 Te0.3 , a structural phase transition occurs in two stages. At higher temperatures, the electronic subsystem undergoes a reconstruction, leading to a significant increase in elastoresistance. 77 Se NMR data show an abrupt change in the relaxation rate during this transition. The final transition occurs at a temperature several degrees below and is also accompanied by anomalies in the electronic properties. Thus, in the Fe(Se,Te) series, similarly to the behavior of pure FeSe under pressure, the type of transition changes and intermediate state appear before the structural transition is suppressed. This similarity between the corresponding phase diagrams is explained by the same deformation of the iron coordination environment in Fe(Se,Te) compounds and in FeSe under pressure. Our findings provide new and significant information on the phase diagram of Fe(Se,Te) compounds and in particular suggest the possible existence of a triple point near the quantum critical point.