Title: Phonon Polaritonics in Two-Dimensional Materials

Abstract

Extreme confinement of electromagnetic energy by phonon polaritons holds the promise of strong and new forms of control over the dynamics of matter. To bring such control to the atomic-scale limit, it is important to consider phonon polaritons in two-dimensional (2D) systems. Recent studies have pointed out that in 2D, splitting between longitudinal and transverse optical (LO and TO) phonons is absent at the Γ point, even for polar materials. Does this lack of LO–TO splitting imply the absence of a phonon polariton in polar monolayers? To answer this, we connect the microscopic phonon properties with the macroscopic electromagnetic response. Specifically, we derive a first-principles expression for the conductivity of a polar monolayer specified by the wave-vector-dependent LO and TO phonon dispersions. In the long-wavelength (local) limit, we find a universal form for the conductivity in terms of the LO phonon frequency at the Γ point, its lifetime, and the group velocity of the LO phonon. Our analysis reveals that the phonon polariton of 2D is simply the LO phonon of the 2D system. For the specific example of hexagonal boron nitride (hBN), we estimate the confinement and propagation losses of the LO phonons, finding that high confinement and reasonablemore » propagation quality factors coincide in regions that may be difficult to detect with current near-field optical microscopy techniques. Finally, we study the interaction of external emitters with 2D hBN nanostructures, finding an extreme enhancement of spontaneous emission due to coupling with localized 2D phonon polaritons and the possibility of multimode strong and ultrastrong coupling between an external emitter and hBN phonons. This may lead to the design of new hybrid states of electrons and phonons based on strong coupling.« less

Authors:

Rivera, Nicholas  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-8298-1468"
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Christensen, Thomas ^[2]; Narang, Prineha  ^[3]

• Search DOE PAGES for author "Narang, Prineha"
• Search DOE PAGES for ORCID "0000-0003-3956-4594"
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+ Show Author Affiliations

1. Harvard Univ., Cambridge, MA (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
3. Harvard Univ., Cambridge, MA (United States)

Publication Date:

2019-03-07

Research Org.:

Energy Frontier Research Centers (EFRC) (United States). Photonics at Thermodynamic Limits (PTL); Krell Institute, Ames, IA (United States); Stanford Univ., CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1566555

Grant/Contract Number:  

FG02-97ER25308; SC0019140

Resource Type:

Accepted Manuscript

Journal Name:

Nano Letters

Additional Journal Information:

Journal Volume: 19; Journal Issue: 4; Journal ID: ISSN 1530-6984

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; optics, phonons; thermal conductivity; charge transport; materials and chemistry by design; mesostructured materials; synthesis (novel materials)