  We experimentally demonstrate a boosted in-plane thermal conduction by
surface plasmon polaritons (SPPs) propagating along a thin Ti film on a glass
substrate. Owing to a lossy nature of metal, SPPs can propagate over
centimeter-scale distance even with a supported metal film, and resulting
ballistic heat conduction can be quantitatively validated. Further, for a
100-nm-thick Ti film on glass substrate, a significant enhancement of in-plane
thermal conductivity compared to bulk value ($\sim 35\%$) is experimentally
shown. This study will provide a new avenue to employ SPPs for heat dissipation
along a supported thin film, which can be readily applied to mitigate hot-spot
issues in microelectronics.
