Suppression of Metallic Transport in Nitrogen-rich Two-Dimensional Transition Metal Nitrides

TL;DR

This study investigates how high nitrogen content in 2D transition metal nitrides causes a transition from metallic to semimetallic behavior, supported by experimental and first-principles calculations.

Contribution

It provides a unified understanding of transport phenomena in nitrogen-rich 2D TMNs and reveals nitrogen content as a key factor in electronic phase transitions.

Findings

Disorder-induced transport mechanism at low temperatures (10-30 K).

Transition from metal to semimetal driven by nitrogen variation.

Suppressed density of states at the Fermi energy in nitrogen-rich TMNs.

Abstract

The recent experimental realization of two-dimensional (2D) transition metal nitrides (TMNs, e.g., Mo5N6, {\delta}-MoN, and W5N6) opens new opportunities for exploring their fundamental physical properties at the two-dimensional limit. In this work, we propose a unified picture of transport phenomena in the nitrogen-rich 2D W5N6 and Mo5N6, and the stoichiometric 2D {\delta}-MoN based on several observations and first-principles calculations. Temperature coefficient of resistance (TCR) and magnetoresistance (MR) from Hall measurements consistently suggest disorder-induced transport mechanism at low temperatures (10-30 K). Notably, we observe a transition from metal to semimetal driven by the variation of nitrogen content in TMNs, supported by the suppressed density of states at the Fermi energy in nitrogen-rich TMNs (e.g. Mo5N6) from first-principle calculations. Carrier density calculations of bulk TMNs and 2D TMNs with -NH termination groups further reveal the switching of majority carrier type of Mo5N6 at reduced thickness, which is in great agreement with Hall measurement results. Our findings demonstrate that high nitrogen content in metallic molybdenum nitrides can induce the transition to a semimetallic phase at the 2D limit, shedding light on both the fundamental aspects of these materials and directions in future material design.