Large ferromagnetic-like band splitting in ultrathin ${\mathrm{SmC}}_{6}$ films

TL;DR

This study synthesizes ultrathin SmC6 films and uses ARPES to reveal large ferromagnetic-like band splitting driven by exchange interactions between Sm 4f moments and conduction electrons, advancing understanding of 2D 4f-electron magnetism.

Contribution

It reports the first synthesis and spectroscopic analysis of ultrathin SmC6 films, demonstrating significant ferromagnetic-like band splitting in 2D 4f-electron systems.

Findings

Large band splitting observed in valence bands due to ferromagnetic order.

Splitting magnitude comparable to Eu- and Gd-based systems.

Surface state splitting can be eliminated by overannealing.

Abstract

Two-dimensional (2D) magnetic materials provide a unique platform for exploring quantum phases from magnetic order in reduced dimensions. While there have been extensive studies on 2D magnetic materials based on 3$d$ electrons, experimental studies on 4$f$-electron counterparts are far fewer, particularly on their electronic structure. In this study, we report the successful synthesis of ultrathin ${\mathrm{SmC}}_{6}$ films using molecular beam epitaxy. Utilizing in situ angle-resolved photoemission spectroscopy (ARPES), we uncover a large band splitting in the valence bands, which we attribute to the ferromagnetic order driven by exchange couplings between Sm 4$f$ moments and conduction electrons. Despite the small magnetic moment of Sm, the observed splitting is comparable to those of Eu- and Gd-based systems with much larger local moments. Interestingly, the surface state also exhibits splitting with similar magnitude and can be eliminated by overannealing, while the valence bands with ferromagnetic-like splittings remain robust. Our work provides spectroscopic insight to understand the electronic origin of magnetic order in Sm-based compounds. Our study also offers a platform to study 2D magnetic materials based on 4$f$ electrons.