## 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)