Oral Presentation

Experimental evidence of existence of residual qusiparticles and their contribution to the properties of MKID resonators at very low temperature

Author(s): Takashi Noguchi Advanced Technology Center, National Astronomical Observatory of Japan

Presenter: Takashi Noguchi (National Astronomical Observatory)

In the Al thin film resonators made by sputtering, the internal quality factor (Q_i) and fractional frequency change (δf_r/f_r) show a peak and a bump near 0.17 K in the respective temperature dependence. It is found that 1/Q_i is well approximated by a - b*ln(T) below 0.15 K, where T is the temperature. This type of temperature dependence strongly indicates the existence of the magnetic impurity scattering of residual quasiparticles due to the Kondo effect.
It is shown that temperature dependence of Q_i and δf_r/f_r observed in the sputtered Al resonators can be well fitted by the theory taking the Kondo effect and kinetic inductance of the residual quasiparticles into account.