# Transition from the Nanoscale to Bulk in the Nonequilibrium Optical Response of Laser-Dressed Materials

## TL;DR

This paper explores how laser-driven materials transition from nanoscale to bulk behavior in their optical properties when far from thermal equilibrium.

## Contribution

The study is the first to investigate the nanoscale-to-bulk transition in nonequilibrium laser-dressed materials using first-principle calculations.

## Key findings

- Nonequilibrium absorption sidebands converge to bulk-like features as system size increases.
- Low-frequency features emerge from Floquet state hybridization and depend on system size.
- Resonant driving transforms nanomaterial absorption peaks into bulk-like features.

## Abstract

Understanding how
the behavior of materials transitions from the
nanoscale to bulk highlights properties where the finite size of matter
matters. To date, such studies have focused on materials at or near
thermal equilibrium, while this transition for strongly driven nonequilibrium
systems is not understood. Here we investigate for the first time
this transition for laser-dressed Floquet-engineered materials where
resonant and nonresonant light is used to drive matter out of thermal
equilibrium, creating an effective nonequilibrium material with properties
that can be very different from those of pristine matter and that
can be triggered on demand. As an archetypical example, we computationally
characterize the linear optical absorption of laser-dressed trans-polyacetylene as a function of chain length, and also
in bulk, using first-principle Hamiltonians and a recently proposed
theory for the nonequilibrium optical response. The computations reveal
nonequilibrium absorption sidebands that converge to equivalent features
for bulk as the size of the system is increased, in a manner akin
to near-equilibrium behavior. The computations also reveal nonequilibrium
low-frequency features that emerge because of hybridization of Floquet
states that show a persistent dependence on system size. We further
demonstrate how resonant driving can be used to transform the isolated
absorption peaks of a nanomaterial into broad bulk-like features.
Overall, this work characterizes the structure–function relations
in Floquet-engineered materials.