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
elasto-hydrodynamic theory describing the low-energy excitations of glassy and amorphous solids
Based on experimental evidence of ordered structure in glasses below MRO (10 → 30˚A) and its lack above, we describe a macroscopic size glass material as elastically coupled, spherical shape, generic blocks, with homogeneous dispersion interaction within each such block.
Origins of double-well potentials (DWP) are discussed and two types of DWPS-Soft and rigid-are emphasised. Soft DWPS
are mainly responsible for low-temperature properties whereas rigid DWPS determine the
properties of glasses at higher temperatures
We introduce a model that includes two types of two level systems (TLSs), which, based on their local symmetry, interact weakly or strongly with the phonon field
We present a novel view of the standard model of tunneling two level systems (TLSs) to explain the
puzzling universal value of a quantity, C ∼ 3 × 10−4, that characterizes phonon scattering in glasses below
1 K as reflected in thermal conductivity, ultrasonic attenuation, internal friction, and the change in sound
we have elucidated aspects implicit in the standard TLS model that include strongly interacting TLSs
[6,7,13], exponentially renormalized tunneling matrix elements [13], and a heretofore unrecognized broad distribution of TLS-phonon couplings
Typical strongly interacting defects have their tunneling suppressed, and observable tunneling occurs
only for TLS which appear to be weakly coupled because their interactions are frustrated
Lubchenko-Wolynesand connections to the glass transition
## Quasi-Classical theories
- Turlakov 2003 [Universal sound absorption in low-temperature glasses](https://knowen-production.s3.amazonaws.com/uploads/attachment/file/4465/Low-temperature%2Bglasses%2BTurlakov%2B2003.pdf)
> 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
> elasto-hydrodynamic theory describing the low-energy excitations of glassy and amorphous solids
- 2021 [Universality of Ultrasonic attenuation in amorphous systems at low temperatures - Pragya Shukla](https://arxiv.org/pdf/2009.00556.pdf)
> Based on experimental evidence of ordered structure in glasses **below MRO (10 → 30˚A)** and its lack above, we describe a macroscopic size glass material as **elastically coupled, spherical shape**, generic blocks, with **homogeneous dispersion interaction within each such block**.
## "Justification of T-TLSs"
- [Burin-Kagan - universal nature - broad distribution of parameters](https://knowen-production.s3.amazonaws.com/uploads/attachment/file/5427/burin-kagan.pdf) 1996 main paper
- [SOME COMMENTS ON THE NATURE OF UNIVERSAL PROPERTIES IN LOW–TEMPERATURE GLASSES](https://arxiv.org/pdf/cond-mat/9609117.pdf)
DAVID R. REICHMAN, PETER NEU, AND ROBERT J. SILBEY
## more parameters - two types, etc
- 1986 Fleurov [Tunnel modes and kinetic properties of glasses at low and high temperatures](https://www.researchgate.net/profile/Victor-Fleurov/publication/230990177_Tunnel_modes_and_kinetic_properties_of_glasses_at_low_and_high_temperatures/links/56d5838b08ae47742115004e/Tunnel-modes-and-kinetic-properties-of-glasses-at-low-and-high-temperatures.pdf)
> Origins of double-well potentials (DWP) are discussed and **two types of DWPS-Soft and rigid-are emphasised**. Soft DWPS
> are mainly responsible for low-temperature properties whereas rigid DWPS determine the
> properties of glasses at higher temperatures
- [Low temperature universality in disordered solids](https://arxiv.org/abs/0910.1283) 2009
M. Schechter, P. C. E. Stamp
> We introduce a model that includes **two types of two level systems (TLSs)**, which, based on their local symmetry, interact weakly or strongly with the phonon field
- [Yu-Carruzzo also explain ....](https://escholarship.org/content/qt5z66f9xv/qt5z66f9xv.pdf?t=qgstny)
> We present a novel view of the standard model of tunneling two level systems (TLSs) to explain the
> puzzling universal value of a quantity, C ∼ 3 × 10−4, that characterizes phonon scattering in glasses below
> 1 K as reflected in thermal conductivity, ultrasonic attenuation, internal friction, and the change in sound
> we have elucidated aspects implicit in the standard TLS model that include strongly interacting TLSs
> [6,7,13], **exponentially renormalized tunneling matrix elements [13], and a heretofore unrecognized broad distribution of TLS-phonon couplings**
- [Frustrated Interactions and Tunneling: Two-Level Systems in Glasses](https://knowen-production.s3.amazonaws.com/uploads/attachment/file/5483/coppersmith.pdf) 1991
S. N. Coppersmith
> Typical **strongly interacting defects have their tunneling suppressed**, and observable tunneling occurs
> only for TLS which appear to be weakly coupled because their interactions are frustrated
## Lubchenko-Wolynesand connections to the glass transition
2001 [The origin of the boson peak and thermal conductivity plateau in low-temperature glasses](https://www.pnas.org/content/pnas/100/4/1515.full.pdf?sid=004706ca-3738-4cc0-807c-870da274a41d)
- [2006 Wolynes-Lyubchenko](https://knowen-production.s3.amazonaws.com/uploads/attachment/file/5430/lyubchenko.pdf)
2005 [The Microscopic Quantum Theory of Low Temperature Amorphous Solids](https://arxiv.org/abs/cond-mat/0506708)
2018 [Low-temperature anomalies in disordered solids: A cold case of contested relics?](https://arxiv.org/abs/1808.02429)
