  We study heat current autocorrelation function and thermal conductivity in
core-shell nanowires by using molecular dynamics simulations. Interestingly, a
remarkable oscillation effect in heat current autocorrelation function is
observed in core-shell NWs, while the same effect is absent in pure silicon
nanowires, nanotube structures and random doped nanowires. Detailed
characterizations of the oscillation signal reveal that this intriguing
oscillation is caused by the coherent resonance effect of the transverse and
longitudinal phonon modes. This phonon resonance results in the localization of
the longitudinal modes, which leads to the reduction of thermal conductivity in
core-shell nanowires. Our study reveals that a coherent mechanism can be used
to tune thermal conductivity in core-shell nanowires.
