# Energy Super-Diffusion in One-Dimensional Momentum Non-Conserving Nonlinear Lattices

## TL;DR

This paper introduces a 1D nonlinear lattice model with negative couplings that breaks momentum conservation and demonstrates energy super-diffusion, challenging previous assumptions about the relationship between momentum conservation and heat conduction behavior.

## Contribution

The study presents a novel 1D nonlinear lattice model with negative couplings that exhibits energy super-diffusion despite momentum non-conservation, revealing new mechanisms for anomalous heat conduction.

## Key findings

- Energy super-diffusion observed in the new model.
- Zero frequency phonon mode induces conserved momentum parity.
- Removing the zero mode leads to normal heat conduction.

## Abstract

There is a well-known mapping between energy normal (super-) diffusion and normal (anomalous) heat conduction in one-dimensional (1D) nonlinear lattices. The momentum conserving nonlinear lattices exhibit energy super-diffusion behavior with the only exception of coupled rotator model. Yet, for all other 1D momentum nonconserving nonlinear lattices studied so far, the energy diffusion or heat conduction is normal. Here we propose a 1D nonlinear lattice model with negative couplings, which is momentum non-conserving due to the translational symmetry breaking. Our numerical results show that energy super-diffusion instead of normal diffusion can be found for this model, which indicates that neither momentum non-conservation is a sufficient condition for energy normal diffusion nor momentum conservation is a necessary condition for energy super-diffusion. Zero frequency phonon mode at Brillouin zone boundary induces a new conserved momentum parity, which is the key for the energy super-diffusion and anomalous heat conduction. Removing the zero frequency mode, such as by on-site potential, is a sufficient condition for normal heat conduction in 1D nonlinear lattices.