Unconventional Resistivity Scaling in Topological Semimetal CoSi

TL;DR

This paper investigates how the resistivity of topological semimetal CoSi scales with thickness, revealing unique behavior due to surface states that could benefit electronic interconnects.

Contribution

It introduces a detailed analysis of resistivity scaling in CoSi, highlighting the role of surface states and defect density, with implications for material engineering.

Findings

Resistivity decreases with decreasing thickness above a critical value when surface conduction dominates.

Resistivity increases with decreasing thickness when bulk conduction dominates at high defect density.

Persistent surface states cause resistivity to decrease even at ultrathin limits, unlike in topological insulators.

Abstract

Nontrivial band topologies in semimetals lead to robust surface states that can contribute dominantly to the total conduction. This may result in reduced resistivity with decreasing feature size contrary to conventional metals, which may highly impact the semiconductor industry. Here we study the resistivity scaling of a representative topological semimetal CoSi using realistic band structures and Green's function methods. We show that there exists a critical thickness d_c dividing different scaling trends. Above d_c, when the defect density is low such that surface conduction dominates, resistivity reduces with decreasing thickness; when the defect density is high such that bulk conduction dominates, resistivity increases in as conventional metals. Below d_c, the persistent remnants of the surface states give rise to decreasing resistivity down to the ultrathin limit, unlike in topological insulators. The observed CoSi scaling can apply to broad classes of topological semimetals, providing guidelines for materials screening and engineering. Our study shows that topological semimetals bear the potential of overcoming the resistivity scaling challenges in back-end-of-line interconnect applications.