# Electronic structure and nematic phase transition in superconducting multi-layer FeSe films grown by pulsed laser deposition method

## TL;DR

This study investigates the electronic structure and nematic phase transition in multilayer FeSe films grown by pulsed laser deposition, revealing higher nematic transition temperatures and effects of electron doping compared to bulk and MBE-grown films.

## Contribution

It provides the first comprehensive ARPES analysis of PLD-grown FeSe/CaF2 films, linking their electronic properties to bulk FeSe and MBE-grown films, and highlights the impact of potassium doping on nematic suppression.

## Key findings

- Nematic transition temperature is 140-160 K, higher than bulk FeSe.
- Potassium doping suppresses nematic order and alters electronic structure.
- PLD-grown FeSe/CaF2 films are more hole-doped than MBE-grown counterparts.

## Abstract

We report comprehensive angle-resolved photoemission investigations on the electronic structure of single crystal multiple-layer FeSe films grown on CaF2 substrate by pulsed laser deposition (PLD) method. Measurements on FeSe/CaF2 samples with different superconducting transition temperatures Tc of 4 K, 9 K and 14 K reveal electronic difference in their Fermi surface and band structure. Indication of the nematic phase transition is observed from temperature-dependent measurements of these samples; the nematic transition temperature is 140-160 K, much higher than 90 K for the bulk FeSe. Potassium deposition is applied onto the surface of these samples; the nematic phase is suppressed by potassium deposition which introduces electrons to these FeSe films and causes a pronounced electronic structure change. We compared and discussed the electronic structure and superconductivity of the FeSe/CaF2 films by PLD method with the FeSe/SrTiO3 films by molecular beam epitaxy (MBE) method and bulk FeSe. The PLD-grown multilayer FeSe/CaF2 is more hole-doped than that in MBE-grown multiple-layer FeSe films. Our results on FeSe/CaF2 films by PLD method establish a link between bulk FeSe single crystal and FeSe/SrTiO3 films by MBE method, and provide important information to understand superconductivity in FeSe-related systems.