Disparate Quantum Corrections to Conduction in Carbon Nanotube Bundles

TL;DR

This study reveals that quantum interference effects in carbon nanotube bundles show disparate coherence lengths depending on the measurement method, indicating complex multi-scale quantum transport within the bundles.

Contribution

It demonstrates that different quantum probes yield inconsistent coherence length estimates in carbon nanotube bundles, challenging the conventional single-scale mesoscopic coherence model.

Findings

Weak localization indicates a ~50 nm coherence length.

Universal conductance fluctuations show coherence over micrometers.

Nonlocal magnetoconductance persists across several micrometers.

Abstract

Quantum interference effects such as weak localization (WL) and universal conductance fluctuations (UCF) normally yield consistent electronic phase-coherence lengths in homogeneous conductors. Here we show that in individual carbon nanotube bundles exfoliated from highly conductive solution-spun fibers, different probes, including the field scales and magnitudes of WL and UCF and nonlocal magnetoconductance, lead to strikingly disparate estimates of coherence lengths. WL magnetoconductance measured in a perpendicular magnetic field yields a phase-coherence length of approximately 50 nm. In contrast, UCF amplitudes are comparable to e squared over h even for an 8 micrometer long segment, and nonlocal magnetoconductance persists across a 4 micrometer separation of electrodes, revealing phase-coherent transport over micrometer length scales within a single bundle. The coexistence of short- and long-range coherence implies that locally diffusive electrons remain partially phase-correlated among nanotubes within the same bundle. These findings challenge the conventional single-scale picture of mesoscopic coherence and establish carbon nanotube bundles as a model platform for emergent, network-level quantum transport.