Substrate Role in Polaron Formation on Single-layer Transition Metal Dihalides

TL;DR

This study explores how different substrates influence polaron formation, species, and mobility in single-layer MnBr₂ grown on various substrates, revealing substrate-dependent behaviors and the importance of substrate modeling.

Contribution

It provides the first detailed analysis of substrate effects on polarons in insulating single-layer MnBr₂, highlighting the role of substrate interactions and periodic potentials.

Findings

Polaron species and densities vary significantly with substrate.

Polarons in MnBr₂ are observable up to 300K.

Mobile polarons can be manipulated with STM tip and guided by substrate-induced potentials.

Abstract

Single-layer transition metal dihalides grown on conducting substrates were shown to host stable polarons. Here, we investigate polarons in insulating single-layer MnBr$_2$ grown by molecular beam epitaxy on three different substrates, namely graphene on Ir(110), graphene on Ir(111), and Au(111). The number densities and species of polarons observed vary strongly as a function of the substrate. For MnBr$_2$ grown on Ir(110) the largest number of polaron species is observed, namely four, of which three show clear similarities with the species observed for CoCl$_2$ on graphite. Polarons in single-layer MnBr$_2$ are observed up to 300K. They can be created, converted, and moved by the STM tip when a tunneling current flows at a proper bias voltage. For graphene on Ir(110) as a substrate, mobile polarons in MnBr$_2$ are guided through the periodic potential imposed from the super-moir\'e resulting from the interaction of MnBr$_2$ with graphene and Ir(110). Our findings indicate that modeling of polarons in such single-layer insulators in contact with a conducting substrate requires to take the substrate explicitly into account.