Experimental evidence of one-dimensional plasma modes in superconducting thin wires

We have studied niobium superconducting thin wires deposited onto a SrTiO3 substrate. By measuring the reflection coefficient of the wires, resonances are observed in the superconducting state in the 130 MHz to 4 GHz range. T hey are interpreted as standing wave resonances of one-dimensional plasma m odes propagating along the superconducting wire. The experimental dispersio n law, omega versus q, presents a linear dependence over the entire wave ve ctor range. The modes are softened as the temperature increases close the s uperconducting transition temperature. Very good agreement is obtained betw een our data and the predicted dispersion relation of one-dimensional plasm a modes.