Experimental tests for the relevance of two-level systems for electron   dephasing
  The relevance of tunneling two-level systems (TLS) for electron dephasing in metals is analyzed. We demonstrate that if the concentration of TLS is sufficient to cause the observed dephasing rate, one also should expect quite substantial effects in the specific heat and ultrasound attenuation. In both cases TLS contribution should dominate the electronic one at low enough temperatures. 
I.L. Aleiner, B.L. Altshuler, and Y. M. Galperin