Synchronizing Bloch-oscillating free carriers in moir\'e flat bands

TL;DR

This paper proposes that moiré graphene flat bands can support Bloch oscillations of free carriers, enabling high-frequency THz applications and potentially leading to THz lasing through synchronized collective oscillations.

Contribution

It demonstrates that moiré superlattices can host Bloch oscillations, offering a new platform for high-frequency electronics and THz laser development.

Findings

Moiré flat bands fulfill conditions for Bloch oscillations.

Emission of a comb-like spectrum of incommensurate frequencies.

Synchronization of oscillations enables THz lasing.

Abstract

Achieving Bloch oscillations of free carriers under a direct current, a long-sought-after collective many-body behavior, has been challenging due to stringent constraints on the band properties. We argue that the flat bands in moir\'e graphene fulfill the basic requirements for observing Bloch oscillations, offering an appealing alternative to the stacked quantum wells used in previous work aiming to access this regime. Bloch-oscillating moir\'e superlattices emit a comb-like spectrum of incommensurate frequencies, a property of interest for converting direct currents into high-frequency currents and developing broad-band amplifiers in THz domain. The oscillations can be synchronized through coupling to an oscillator mode in a photonic or plasmonic resonator. Phase-coherent collective oscillations in the resonant regime provide a realization of current-pumped THz lasing.