Solvated electrons in polar liquids as epsilon-near-zero materials tunable in the terahertz frequency range

TL;DR

This study demonstrates that solvated electrons in polar liquids act as epsilon-near-zero materials in the terahertz range, with tunable properties affecting light propagation, supported by experimental and theoretical analysis.

Contribution

It reveals the ENZ behavior of solvated electrons in polar liquids at THz frequencies and provides a combined experimental and theoretical investigation.

Findings

Observation of ENZ behavior in polar liquids with solvated electrons

Modification of phase and group velocities around the resonance frequency

Broadening of THz pulse envelope below the resonance frequency

Abstract

Electrons in polar liquids give rise to a polaron resonance at a terahertz (THz) frequency \nu_0 depending on electron concentration. The impact of this resonance on light propagation is studied in experiments, where a femtosecond pump pulse generates electrons via multiphoton ionization and a THz probe pulse propagated through the excited sample is detected in a phase-resolved way. We observe a behavior characteristic for epsilon-near-zero (ENZ) materials with strongly modified phase and group velocities around \nu_0, and a broadening of the THz pulse envelope below \nu_0. Calculations based on a local-field approach reproduce the ENZ behavior.