# Incoherent-coherent crossover and the pseudogap in Te-annealed superconducting Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ revealed by magnetotransport measurements

## TL;DR

This study uses magnetotransport measurements on Te-annealed Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ crystals to reveal a temperature-dependent crossover from incoherent to coherent electronic states and the pseudogap's role in enabling superconductivity.

## Contribution

It demonstrates the relationship between electronic coherence, pseudogap formation, and superconductivity in Te-annealed Fe-based superconductors, highlighting the importance of removing excess iron.

## Key findings

- Incoherent to coherent crossover occurs around 150 K for x=0.2.
- A pseudogap opens at high temperatures and becomes more prominent at lower temperatures.
- Coherent state with pseudogap is essential for superconductivity in this system.

## Abstract

In this study, we conducted various magnetotransport measurements on Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ single crystals from which excess iron was sufficiently removed. Our results revealed that crossover from the incoherent to the coherent electronic state and opening of the pseudogap occur at high temperatures ($\approx$ 150 K for $x$ = 0.2). This is accompanied by a more substantial pseudogap and the emergence of a phase with a multi-band nature at lower temperatures (below $\approx$ 50 K for $x$ = 0.2) before superconductivity sets in. A comparison of these results with those of the as-grown (non-superconducting) samples implies that the coherent state accompanied by the pseudogap is needed for the occurrence of superconductivity in this system.