Switching Nanoscale Temperature Fields with High-Order Plasmonic Modes in Transition Metal Nanorods

Metal nanostructures exhibit various plasmonic modes, including dipolar, quadrupolar, and hexapolar modes, depending on photo-irradiation conditions. In the present work, we numerically demonstrated that these high-order plasmonic modes can be used to switch nanoscale temperature distributions in plasmonic heating of a manganese (Mn) nanorod; the key feature of Mn is its low thermal conductivity. In general, when noble metal nanostructures are used for the plasmonic heating, nanostructure surface will be almost isothermal regardless of the order of the excited plasmonic modes, because of high thermal conductivities of noble metals: e.g. a themal conductivity of gold is 314 [W m−1K−1]. However, in contrast to noble metals, Mn possesses a significantly lower thermal conductivity of 7.8 [W m−1K−1]. Due to this lower thermal conductivity value, the distinct spatial characteristics of high-order plasmonic modes can be clearly transcribed into nanoscale temperature fields; this is achieved through the generation of polarization currents by the high-order plasmons within the nanorod. These findings strongly suggest that high-order plasmonic modes hold significant potential for advanced and precise manipulation of heat generation at the nanometer scale in the field of thermoplasmonics.