Sagnac interference in carbon nanotubes

Abstract

The Sagnac interference mode arises when two interfering counterpropogating beams traverse a loop, but with their velocities detuned by a small amount $2u$, with ${v}_{R/L}={v}_{F}\ifmmode\pm\else\textpm\fi{}u$. In this paper we perform a perturbative nonequilibrium calculation of Sagnac interference in single-channel wires as well as armchair nanotube loops. We study the dependence of the Sagnac conductance oscillations on temperature and interactions. We find that the Sagnac interference is not destroyed by strong interactions, but becomes weakly dependent on the velocity detuning $u$. In armchairs nanotubes with typical interaction strength, $0.25\ensuremath{\le}g\ensuremath{\le}0.5$, we find that the necessary temperature for observing the interference effect, ${T}_{\text{SAG}}$ is also only weakly dependent on the interaction, and is enhanced by a factor of 8 relative to the temperature necessary for observing Fabry-P\'erot interference in the same system, ${T}_{\text{FP}}$.