An accurate determination of the excess low temperature heat capacity of a superconducting metallic glass

The specific heat of an amorphous superconductor Zr₃Rh (T_{c = 4.3 K}) has been measured in the temperature range from 0.35 K to 10 K and with an applied magnetic field of 75 kG. The high field suppresses superconductivity and allows accurate determination of the phonon (βT³) term for the lowest temperatures studied. A careful subtraction of the normal electronic specific heat (γT) and phonon terms reveals a well defined excess linear heat capacity γ'T at low temperature. This excess term is attributed to localized lattice excitations using the two-level tunneling defect model of Phillips.