# Optical Spectroscopy of SmN: Evidence for 4f Transport

## TL;DR

This study uses optical spectroscopy to demonstrate that the 4f band forms the bottom of the conduction band in samarium nitride, supporting its semiconducting nature and the role of 4f transport in its properties.

## Contribution

It provides direct optical evidence that the 4f band is at the conduction band minimum in SmN, clarifying its electronic structure and transport mechanisms.

## Key findings

- 4f band forms the bottom of the conduction band
- No free carrier absorption at low energies
- Supports semiconducting ground state

## Abstract

The rare-earth nitride ferromagnetic semiconductors owe their varying magnetic properties to the progressive filling of 4f shell across the series. Recent electrical transport measurements on samarium nitride, including the observation of superconductivity, have been understood in terms of a contribution from a 4f transport channel. Band structure calculations generally locate an empty majority 4f-band within the conduction band although over a wide range of possible energies. Here we report optical reflection and transmission measurements on samarium nitride between 0.01 eV to 4 eV, that demonstrate clearly that the 4f band forms the bottom of the conduction band. Results at the lowest energies show no free carrier absorption, indicating a semiconducting ground state, and supporting earlier conclusions based on transport measurements.