Tuning electronic structure topology of rare-earth monopnictides by dimensionality reduction and epitaxial strain*

Rare-earth monopnictide (RE-V) semimetal crystals exhibit intriguing trends in magnetoresistance, magnetic ordering, and electronic phase transitions under various stimuli. This study demonstrates that the electronic phase of RE-V materials can be manipulated through dimensionality reduction and epitaxial strain. First, when the thickness of (001)-oriented RE-V films, such as LaSb, is reduced to 7, 5, or 3 monolayers, quantum spin Hall (QSH) insulator phases emerge due to quantum confinement effects (QCE) on in-plane electron pockets and the absence of quantum confinement on out-of-plane pockets. This results in a band inversion with an opening of a nontrivial band gap driven by strong spin-orbit coupling in ultrathin films [1]. Secondly, our work investigates the evolution of band topology in biaxially strained GdSb (001) epitaxial films, which exhibit continuous tuning of electronic structure from topologically trivial to nontrivial under strain. Biaxial strain narrows the gap between hole and electron bands along the [001] direction, as confirmed through angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) [2]. Considerations of orbital symmetry offer a robust explanation for conduction and valence band shifts. These findings, expected to be common features in rare-earth monopnictides, shed light on the fascinating behavior of RE-V semimetals under the influence of strain and quantum confinement effects.