THE SPECIFIC-HEAT AND UPPER CRITICAL-FIELD B-C2(T) OF AMORPHOUS CUXSN100-X - ELECTRONIC AND VIBRATIONAL EXCITATIONS

The specific heat C of amorphous CuxSn100-x films (10 less than or equ al to x less than or equal to 70) was investigated between 0.3 K and 7 K in the superconducting state as well as in the normal state using a modified AC method. The analysis of the data allows one to determine the electronic density of states at the Fermi energy D(E(F)), the dens ity of states of low-energy excitations n(0) and the Debye temperature Theta(D). The concentration dependence of D(E(F)) shows a pronounced minimum at x = 60 at.% in comparison to the free-electron model, in ag reement with specific heat and UPS measurements and theoretical calcul ations published recently. The specific heat of the low-energy excitat ions is of the same order of magnitude as data available from the lite rature, and shows a linear temperature dependence. Theta(D) increases with copper concentration and the values agree with those published re cently. In addition, the critical magnetic field B-c2(T) of the same f ilms was measured. The analysis of these data which should be valid fo r strongly disordered superconductors yields values of D(E(F)) which a re about 20% higher than those determined by specific heat measurement s. Arguments are given as to why values taken from critical field meas urements might be too high. Finally, the specific heat of an amorphous Au-70-Sn-30 film was measured. D(E(F)) was found to be 30% below the free-electron model value, in contrast to results published previously by Rieger and Baumann who found D(E(F)) to be in accordance with the free-electron model.