Specific heat of an icosahedral superconductor, Mg3Zn3Al2

Specific-heat measurements are reported for cubic (c), icosahedral (i), and amorphous (a) phases of Mg₃Zn₃Al₂ in the temperature range 0.04-5 K. All three phases are superconducting, with T_c=0.32, 0.41, and 0.75 K, respectively. The electronic density of states N(0) is comparable to that expected in the free-electron model for all three phases. Compared to the c phase, significant lattice softening is observed in the i phase and, especially, in the a phase, indicating an increase in the electron-phonon coupling parameter λ with decreasing order.