Observation of Giant Quantized Phonon Modes in Graphene via Tunneling Spectra

TL;DR

This study directly observes giant quantized phonon modes in graphene using tunneling spectra under magnetic fields, revealing new inelastic tunneling channels and controllable phonon interactions at the nanoscale.

Contribution

It demonstrates the first direct measurement of quantized phonon modes in graphene via tunneling spectra and shows how these modes can be controlled by substrate interactions.

Findings

Giant quantized phonon peaks observed in graphene tunneling spectra.

Phonon peaks are about 50 times stronger than Landau level signals.

Phonon modes can be switched on or off by substrate interactions.

Abstract

Phonons, the fundamental vibrational modes of a crystal lattice, play a crucial role in determining electronic properties of materials through electron-phonon interaction. However, it has proved difficult to directly probe the phonon modes of materials in electrical measurements. Here, we report the observation of giant quantized phonon peaks of the K and K out-of-plane phonon in graphene monolayer in magnetic fields via tunneling spectra, which are usually used to measure local electronic properties of materials. A perpendicular magnetic field quantizes massless Dirac fermions in graphene into discrete Landau levels (LLs). We demonstrate that emission or absorption of phonons of quasiparticles in the LLs of graphene generates a new sequence of discrete states: the quantized phonon modes. In our tunneling spectra, the intensity of the observed phonon peaks is about 50 times larger than that of the LLs because that the K and K out-of-plane phonon opens an inelastic tunneling channel. We also show that it is possible to switch on off the quantized phonon modes at nanoscale by controlling interactions between graphene and the supporting substrate.