Mechanism and modulation of terahertz generation from a semimetal - graphite

TL;DR

This paper investigates how terahertz waves are generated from graphite, a bulk semi-metal, revealing the underlying mechanism and how to optimize the signal for potential applications in graphene-based terahertz devices.

Contribution

It experimentally demonstrates the modulation of terahertz signals from graphite and elucidates the surface field-driven mechanism, highlighting differences from semiconductors and temperature independence.

Findings

Terahertz signals are driven by surface fields inducing transient currents.

Graphite shows no temperature dependence from room temperature to 80°C.

Understanding this mechanism aids in optimizing terahertz devices based on semi-metals or graphene.

Abstract

Semi-metals might offer a stronger interaction and a better confinement for terahertz wave than semiconductors, while preserve tunability. Particularly, graphene-based materials are envisioned as terahertz modulators, filters and ultra-broadband sources. However, the understanding of terahertz generation from those materials is still not clear, thus limits us recognizing the potential and improving device performances. Graphite, the mother material of graphene and a typical bulk semi-metal, is a good system to study semi-metals and graphene-based materials. Here we experimentally modulate and maximize the terahertz signal from graphite surface, thus reveal the mechanism - surface field driving photon induced carriers into transient current to radiate terahertz wave. We also discuss the differences between graphite and semiconductors; particularly graphite shows no temperature dependency from room temperature to 80C. Above knowledge will help us understand terahertz generations, achieve maximum output and electric modulation, in semi-metal or graphene based devices.