Discovery of two-dimensional Dirac nodal line fermions in monolayer Cu2Si

TL;DR

This paper reports the discovery of two-dimensional Dirac nodal line fermions in monolayer Cu2Si, combining theoretical and experimental methods, revealing new topological features in 2D materials with potential for advanced electronic devices.

Contribution

It provides the first experimental evidence of 2D Dirac nodal line fermions in Cu2Si, expanding the understanding of topological semimetals in two dimensions.

Findings

Dirac nodal lines form two concentric loops around the Γ point

Nodal lines are protected by mirror reflection symmetry

Cu2Si is a new platform for studying 2D Dirac physics

Abstract

Topological nodal line semimetals, a novel quantum state of materials, possess topologically nontrivial valence and conduction bands that touch at a line near the Fermi level. The exotic band structure can lead to various novel properties, such as long-range Coulomb interaction and flat Landau levels. Recently, topological nodal lines have been observed in several bulk materials, such as PtSn4, ZrSiS, TlTaSe2 and PbTaSe2. However, in two-dimensional materials, experimental research on nodal line fermions is still lacking. Here, we report the discovery of two-dimensional Dirac nodal line fermions in monolayer Cu2Si based on combined theoretical calculations and angle-resolved photoemission spectroscopy measurements. The Dirac nodal lines in Cu2Si form two concentric loops centred around the {\Gamma} point and are protected by mirror reflection symmetry. Our results establish Cu2Si as a new platform to study the novel physical properties in two-dimensional Dirac materials and provide new opportunities to realize high-speed low-dissipation devices.