Two nearly universal and anomalous properties of glasses, the peak in the
specific heat and plateau of the thermal conductivity, occur around the same
temperature. This coincidence suggests that the two phenomena are related. Both
effects can be rationalized by assuming Rayleigh scaling of sound attenuation
and this scaling leads one to consider scattering from defects. Identifying
defects in glasses, which are inherently disordered, is a long-standing problem
that was approached in several ways. We examine candidates for defects in
glasses that represent areas of strong sound damping. We show that some defects
are associated with quasi-localized excitations, which may be associated with
modes in excess of the Debye theory. We also examine generalized Debye
relations, which relate sound damping and the speed of sound to excess modes.
We derive a generalized Debye relation that does not resort to an approximation
used by previous authors. We find that our relation and the relation given by
previous authors are almost identical at small frequencies and also reproduce
the independently determined density of states. Jedoch, the different
generalized Debye relations do not agree around the boson peak. While
generalized Debye relations accurately predict the boson peak in
two-dimensional glasses, they under estimate the boson peak in
three-dimensional glasses.

Dieser Artikel untersucht Zeitreisen und deren Auswirkungen.

PDF herunterladen: