# Bulk superconductivity and role of fluctuations in the iron-based superconductor FeSe at high pressures

## TL;DR

This study investigates how pressure influences bulk superconductivity and magnetic fluctuations in FeSe, revealing a complex interplay that resembles behaviors seen in cuprate superconductors.

## Contribution

It provides the first thermodynamic evidence of bulk superconductivity across a wide pressure range and highlights the role of fluctuations in FeSe.

## Key findings

- Superconductivity remains bulk across all pressures studied.
- Magnetic and superconducting fluctuations coexist over a broad temperature range.
- Superconductivity competes with magnetism in FeSe.

## Abstract

The iron-based superconductor FeSe offers a unique possibility to study the interplay of superconductivity with purely nematic as well magnetic-nematic order by pressure (p) tuning. By measuring specific heat under p up to 2.36GPa, we study the multiple phases in FeSe using a thermodynamic probe. We conclude that superconductivity is bulk across the entire p range and competes with magnetism. Our analysis suggests that superconducting and magnetic fluctuations exist over a wide temperature range above the respective bulk transition temperatures, whenever magnetism is present. These observations highlight similarities between FeSe and underdoped cuprate superconductors where fluctuations play a crucial role.