BPeak and TLSs - P
Turlakov 2004 Universal sound absorption in low-temperature glasses
M. Turlakov, Phys. Rev. Lett., 93, 035501, (2004).
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Phenomenologically assuming a sharp decrease of shear relaxation time for large wavevector k > kξ
density modes (where kξ is of order of inverse of several interatomic distances a), I develop a general
only $\omega^4$ density of states for oscillators with disorder
no dipole interaction
2020 A new paradigm for the low-T glassy-like thermal properties of solids
New experimental and theoretical observations have questioned the origin of the boson peak and the linear in T specific heat exclusively from disorder and TLS.
The linear in T behavior in the specific heat is stronger as the modes are more localized and crosses over to a $T^3$ (Debye) regime at a temperature $T^\star \sim \sqrt{ v^3/D}$, where v is the speed of sound.
2007 Vibrational instability, two-level systems, and the boson peak in glasses
D. A. Parshin
In summary, we have shown that the same physical mechanism is fundamental for such seemingly different phenomena as the formation of the two-level systems in glasses and the boson peak in the reduced density of low-frequency
vibrational states. In this way, **two of the most fundamental properties of glasses are interconnectedIn our theory, it follows naturally. The physical reason for the small value of the parameter C is that only a small fraction of all created TLS’s can actually tunnel in realistic time scales.