Molecular beam epitaxy and electronic structures of rare-earth selenide EuSe thin films

The rare-earth Eu-based compound EuSe has attracted widespread attention due to its unique half-filled 4f orbital with large orbital momentum and strong correlation effects. Here, we realize the molecular beam epitaxial (MBE) growth of high-quality EuSe thin films on SrTiO3(001) and bilayer graphene (BLG) substrates. The EuSe grown on SrTiO3 substrate forms an out-of-plane (001) facet single-crystalline film, with the in-plane orientation EuSe〈110〉 direction paralleled to the SrTiO3〈100〉 direction. In contrast, the EuSe film grown on the BLG substrate has various in-plane rotational domains. The electronic band structures of the EuSe films are experimentally characterized by in situ angle-resolved photoemission spectroscopy, showing a semiconductive nature with the Eu 4f band as the top of the valence band. The bandgap size of EuSe grown on BLG is further determined as about 2.8 eV via low-temperature scanning tunneling spectroscopy. The MBE growth and the electronic structure characterizations of the EuSe thin films would promote further research and applications on the half-filled 4f electrons of rare-earth Eu-based compounds.