Modeling of networks and globules of charged domain walls observed in pump and pulse induced states

TL;DR

This study models the formation of nanoscale networks and globules of charged domain walls in layered materials, explaining experimental observations of pattern formation linked to phase transitions and hidden states.

Contribution

It introduces a classical charged lattice gas model that reproduces the observed domain wall patterns and explains void aggregation through charge fractionalization.

Findings

Patterns resemble experimental STM images

Void coalescence into domain walls and networks observed

Charge fractionalization explains void aggregation

Abstract

Experiments on optical and STM injection of carriers in layered $\mathrm{MX_2}$ materials revealed the formation of nanoscale patterns with networks and globules of domain walls. This is thought to be responsible for the metallization transition of the Mott insulator and for stabilization of a "hidden" state. In response, here we present studies of the classical charged lattice gas model emulating the superlattice of polarons ubiquitous to the material of choice $1T-\mathrm{TaS_2}$. The injection pulse was simulated by introducing a small random concentration of voids which subsequent evolution was followed by means of Monte Carlo cooling. Below the detected phase transition, the voids gradually coalesce into domain walls forming locally connected globules and then the global network leading to a mosaic fragmentation into domains with different degenerate ground states. The obtained patterns closely resemble the experimental STM visualizations. The surprising aggregation of charged voids is understood by fractionalization of their charges across the walls' lines.