Soft Transverse Phonons in a Metallic Glass

The acoustic properties and low-temperature specific heat of a dense metallic glass in bulk form have been studied for the first time. A large softening of long-wavelength transverse acoustic phonons in ${\mathrm{Pd}}_{0.775}$ ${\mathrm{Si}}_{0.165}$ ${\mathrm{Cu}}_{0.06}$ glass, relative to the crystal, is observed which is not simply attributable to the small density difference between the two states.