# Anharmonic soft modes in glasses

## TL;DR

This paper introduces an unstable core version of the soft potential model to explain low-temperature anomalies in glasses, linking numerical findings and experimental evidence for boson peak modes.

## Contribution

It formulates a new unstable core soft potential model and connects recent numerical and experimental findings to this framework.

## Key findings

- Unstable core soft modes are relevant to low-temperature anomalies.
- Numerical low-barrier relaxation findings relate to the soft potential model.
- Experimental evidence supports the unstable core of boson peak modes.

## Abstract

The anharmonic soft modes studied in recent numerical work in the glass phase of simple liquids have an unstable core, stabilized by the positive restoring forces of the surrounding elastic medium. The present paper formulates an unstable core version of the phenomenological soft potential model for the low temperature anomalies of glasses, relates a new numerical finding on low-barrier relaxations to old soft potential model results, and discusses experimental evidence for an unstable core of the boson peak modes.