Tunneling Systems in Icosahedral MgZnA1 Observed in Elastic Measurements

We report the first observation of tunneling systems (TS) in a quasicrystal, Mg3Zn3Al2. The evidence for the TS comes from low frequency, low temperature elastic measurements performed with a vibrating reed technique. We see changes in the sound velocity below the superconducting transition Tc=0.4K due to both resonant and relaxational interactions with the TS. This behavior is similar to that seen in some superconducting metallic glasses. We have also measured an icosahedral sample of Al74Si6Mn20, where we see a strong increase in the velocity below 0.025K. Any effects due to disorder are hidden by this stronger behavior, which we tentatively attribute to the magnetic properties of the sample.