Electronic phase diagram in Te-annealed superconducting FeTe$_{1-x}$Se$_x$ revealed by magnetic susceptibility

TL;DR

This study maps the doping-temperature phase diagram of Te-annealed FeTe$_{1-x}$Se$_x$ superconductors using magnetic susceptibility, revealing pseudogap formation, carrier concentration changes, and significant superconducting fluctuations possibly linked to BCS-BEC crossover.

Contribution

It provides new insights into the electronic phase diagram of FeTe$_{1-x}$Se$_x$ superconductors, highlighting characteristic temperatures and fluctuation phenomena through magnetic susceptibility measurements.

Findings

Identification of two characteristic temperatures T*_{ ext{chi}} and T**_{ ext{chi}}.

Observation of pseudogap opening below T**_{ ext{chi}}.

Detection of large superconducting fluctuations possibly related to BCS-BEC crossover.

Abstract

Knowledge of the doping (x)-temperature (T) phase diagram of Fe-based superconductors is crucial in understanding the mechanism of high transition temperature superconductivity. Here, we measured the Se doping dependence of the magnetic susceptibility for Te-annealed FeTe$_{1-x}$Se$_x$. Two characteristic temperatures $T^*_{\chi}$ and $T^{**}_{\chi}$ were observed in the temperature dependence of magnetic susceptibility, where the magnetic susceptibility decreased below T$^{**}_{\chi}$ and tended to increase with further decreasing temperature below T$^*_{\chi}$. The decrease in magnetic susceptibility below T$^{**}_{\chi}$ is considered to be due to the opening of the pseudogap. Whereas the increase in magnetic susceptibility below T$^*_{\chi}$ is attributed to the increase in the carrier concentration of electrons. Furthermore, we found the large superconducting fluctuation, which may be related to BCS-BEC crossover.