Electronic topological transition of 2D boron by the ion exchange reaction

TL;DR

This study explores how ion exchange reactions induce electronic topological transitions in 2D boron structures, revealing changes from semimetallic to insulating states through spectroscopic and computational methods.

Contribution

It demonstrates the ability to control electronic topology in borophene via ion exchange, a novel approach for tuning 2D material properties.

Findings

Hydrogenated borophene is a Dirac nodal loop semimetal ($Z_2=-1$).

YCrB$_4$ layered crystal is an insulator ($Z_2=1$).

Ion exchange induces topological electronic transitions.

Abstract

We systematically investigated electronic evolutions of non-symmorphic borophene with chemical environments that were realized by the ion exchange method. Electronic structures can be characterized by the topological $Z_2$ invariant. Spectroscopic experiments and DFT calculations unveiled that a sheet of hydrogenated borophene (borophane) is the Dirac nodal loop semimetal ($Z_2=-1$), while a layered crystal of YCrB$_4$ is an insulator ($Z_2=1$). The results demonstrate the electronic topological transition by replacement of the counter atoms on the non-symmorphic borophene layer.