Directional massless Dirac fermions in a layered van der Waals material with one-dimensional long-range order

TL;DR

This paper reports the discovery of directional massless Dirac fermions in a layered van der Waals material, caused by one-dimensional structural modulation, with implications for nano-electronic device engineering.

Contribution

It reveals a novel 1D Dirac fermion phenomenon in NbSi0.45Te2, protected by nonsymmorphic symmetry, expanding understanding of electron behavior in layered materials.

Findings

Identification of 1D Dirac fermions via ARPES

Structural modulation causes 1D confinement of carriers

Protection of Dirac node by nonsymmorphic symmetry

Abstract

Exotic properties in single or few layers of van der Waals materials carry great promise for applications in nanoscaled electronics, optoelectronics and flexible devices. The established, distinct examples include extremely high mobility and superior thermal conductivity in graphene, a large direct band gap in monolayer MoS2 and quantum spin Hall effect in WTe2 monolayer, etc. All these exotic properties arise from the electron quantum confinement effect in the two-dimensional limit. Here we report a novel phenomenon due to one-dimensional (1D) confinement of carriers in a layered van der Waals material NbSi0.45Te2 revealed by angle-resolved photoemission spectroscopy, i.e. directional massless Dirac fermions. The 1D behavior of the carriers is directly related to a stripe-like structural modulation with the long-range translational symmetry only along the stripe direction, as perceived by scanning tunneling microscopy experiment. The four-fold degenerated node of 1D Dirac dispersion is essential and independent on band inversion, because of the protection by nonsymmorphic symmetry of the stripe structure. Our study not only provides a playground for investigating the striking properties of the essential directional massless Dirac fermions, but also introduces a unique monomer with 1D long-range order for engineering nano-electronic devices based on heterostructures of layered van der Waals materials.