Taming quantum interference: a route to high electrical conductance in carbon nanotube assemblies

Miniaturized electronics require lightweight conductors that maintain high conductance under demanding conditions. CNT networks are promising candidates, but their transport is governed by inter-nanotube junctions where electron waves interfere. Controlling this interference requires understanding how junction architecture shapes transmission. We explore coherent transport through experimentally relevant junctions, from single and multiple single-walled CNT (SWCNT) contacts to double-walled CNT (DWCNT) and triple-walled CNT (TWCNT) junctions, with atomistic tight-binding non-equilibrium Green's-function calculations, also under a perpendicular magnetic field. We use analytically solvable minimal models to identify transport regimes expected for quasi-1D nanoscale junctions, and an electron-waveguide picture to interpret their CNT-specific manifestations. For single SWCNT--SWCNT junctions, high-transmission windows are set mainly by overlap length, doping and magnetic field. Gateway states can enhance conductance when some CNT subbands are gapped, and in some cases a magnetic field can restore transmission by lifting an interference blockade. In more complex architectures, added paths become selective: multi-junctions generate resonant filtering, while additional walls redistribute transmission instead of acting as independent channels. DWCNT junctions remain outer-wall dominated and SWCNT-like, whereas TWCNT junctions become genuinely multi-channel and more field-sensitive. This explains the lower, more field-sensitive conductance of multi-walled CNT (MWCNT) fibres, in accord with our ultrahigh-field measurements on SWCNT and MWCNT fibres. Ultimately, this work turns microscopic interference mechanisms into design principles for high-conductance, field-stable CNT conductors.