# Low temperature universality in disordered solids

## TL;DR

This paper presents a model explaining the universal low-temperature properties of disordered solids by incorporating two types of two-level systems with different interactions, successfully matching experimental observations and addressing longstanding questions.

## Contribution

The paper introduces a novel model with two types of TLSs to explain low-temperature universality in disordered solids, linking local symmetry to phonon interactions.

## Key findings

- Model accounts for experimental phonon attenuation data
- Explains the energy scale of 3K for universality
- Addresses the nature and universality of TLSs in disordered systems

## Abstract

The low temperature universal properties in disordered and amorphous solids are considered. 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. This accounts well for the experimental results, and addresses some long-standing questions: the nature of the TLSs; the smallness and universality of the phonon attenuation, and the energy scale of $3$K below which universality is observed. Our model describes disordered lattices; we also discuss its application to amorphous solids.