NMR Probe of Metallic States in Nanoscale Topological Insulators

TL;DR

This study uses NMR to investigate how reducing particle size in bismuth telluride nanoparticles enhances metallic behavior, revealing a transition in electronic properties linked to surface effects.

Contribution

It provides the first detailed NMR analysis of size-dependent metallicity and electronic transitions in nanoscale topological insulators.

Findings

Enhanced spin-lattice relaxation below 33 nm

Transition from single to bimodal NMR spectra

Increased metallicity with higher surface-to-volume ratio

Abstract

A 125Te NMR study of bismuth telluride nanoparticles as function of particle size revealed that the spin-lattice relaxation is enhanced below 33 nm, accompanied by a transition of NMR spectra from single to bimodal regime. The satellite peak features a negative Knight shift and higher relaxivity, consistent with core polarization from p-band carriers. Whereas nanocrystals follow a Korringa law in the range 140-420K, micrometer particles do so only below 200K. The results reveal increased metallicity of these nanoscale topological insulators in the limit of higher surface-to-volume ratios.