# Thickness-dependent electron momentum relaxation times in thin iron films

## TL;DR

This study investigates how electron momentum relaxation times in iron thin films vary with thickness, revealing that thinner films have faster response times and increased variance in microscopic relaxation times, influenced by electron species and confinement effects.

## Contribution

It provides the first detailed analysis of thickness-dependent electron relaxation times in iron films using terahertz conductivity measurements, highlighting the role of electron species and confinement.

## Key findings

- Thinner iron films exhibit shorter response times.
- Variance of microscopic relaxation times increases with film thickness.
- Different electron species contribute to conduction with distinct relaxation times.

## Abstract

Terahertz time-domain conductivity measurements in 2 to 100 nm thick iron films resolve the femtosecond time delay between applied electric fields and resulting currents. This response time decreases for thinner metal films. The macroscopic response time depends on the mean and the variance of the distribution of microscopic momentum relaxation times of the conducting electrons. Comparing the recorded response times with DC-conductivities demonstrates increasing variance of the microscopic relaxation times with increasing film thickness. At least two electron species contribute to conduction in bulk with substantially differing relaxation times. The different electron species are affected differently by the confinement because they have different mean free paths.