Generating coherent phonon waves in narrow-band materials: a twisted bilayer graphene phaser

TL;DR

This paper proposes a novel device called the 'phaser' that uses twisted bilayer graphene to generate coherent terahertz phonon beams via stimulated emission, enabling advanced control of quantum states and new THz technologies.

Contribution

It introduces a new phonon lasing mechanism in TBG, leveraging slow-electron bands to produce coherent THz acoustic phonons, a significant advancement over prior methods.

Findings

Proposes a TBG-based phonon laser device (phaser).

Demonstrates potential for generating coherent THz phonons.

Highlights applications in quantum control and THz technology.

Abstract

Twisted bilayer graphene (TBG) exhibits extremely low Fermi velocities for electrons, with the speed of sound surpassing the Fermi velocity. This regime enables the use of TBG for amplifying vibrational waves of the lattice through stimulated emission, following the same principles of operation of free-electron lasers. Our work proposes a lasing mechanism relying on the slow-electron bands to produce a coherent beam of acoustic phonons. We propose a device based on undulated electrons in TBG, which we dub the phaser. The device generates phonon beams in a terahertz (THz) frequency range, which can then be used to produce THz electromagnetic radiation. The ability to generate coherent phonons in solids breaks new ground in controlling quantum memories, probing quantum states, realizing non-equilibrium phases of matter, and designing new types of THz optical devices.