Femtosecond photo-switching of interface polaritons in black phosphorus heterostructures

Abstract

The possibility of hybridizing collective electronic motion with mid-infrared light to form surface polaritons has made van der Waals layered materials a versatile platform for extreme light confinement and tailored nanophotonics. Graphene and its heterostructures have attracted particular attention because the absence of an energy gap allows plasmon polaritons to be tuned continuously. Here, we introduce black phosphorus as a promising new material in surface polaritonics that features key advantages for ultrafast switching. Unlike graphene, black phosphorus is a van der Waals bonded semiconductor, which enables high-contrast interband excitation of electron-hole pairs by ultrashort near-infrared pulses. Here, we design a SiO/black phosphorus/SiO heterostructure in which the surface phonon modes of the SiO layers hybridize with surface plasmon modes in black phosphorus that can be activated by photo-induced interband excitation. Within the Reststrahlen band of SiO, the hybrid interface polariton assumes surface-phonon-like properties, with a well-defined frequency and momentum and excellent coherence. During the lifetime of the photogenerated electron-hole plasma, coherent hybrid polariton waves can be launched by a broadband mid-infrared pulse coupled to the tip of a scattering-type scanning near-field optical microscopy set-up. The scattered radiation allows us to trace the new hybrid mode in time, energy and space. We find that the surface mode can be activated within ∼50 fs and disappears within 5 ps, as the electron-hole pairs in black phosphorus recombine. The excellent switching contrast and switching speed, the coherence properties and the constant wavelength of this transient mode make it a promising candidate for ultrafast nanophotonic devices.

Black phosphorus nanodevices at terahertz frequencies: Photodetectors and future challenges

“…In particular, femtosecond pulses can initiate the plasmonic response in this semiconductor through direct excitation of electrons across the bandgap. The reported switching speed (50 fs) of activated phonon-plasmon-polariton modes in SiO 2 /BP/SiO 2 heterostructures 25 opens an intriguing …”

“…For example, owing to its ultrafast nonlinear optical response, it has been proposed as a saturable absorber in the telecom band (1400 nm-1600 nm) for the realization of passively mode-locked lasers. 24 Recently, Huber et al 25 revealed the ultrafast (∼50 fs) switching dynamics of interface polaritons in SiO 2 /BP/SiO 2 heterostructures. The spectral purity and coherence of the activated phonon-plasmon-polariton modes can provide a versatile and robust technological platform for polariton-based mid-infrared optoelectronic devices and, remarkably, for ultrafast plasmonic applications.…”

Nonlocal plasmonic response of doped and optically pumped graphene, MoS2 , and black phosphorus

“…The ultrafast response of optically heated graphene has been probed through pump-probe spectroscopy and has been shown to sustain plasmons induced by an elevated electron temperature [9,16]. Likewise, optical heating of BP has been also demonstrated to enable plasmons in the material [17]. Optical pumping causes electrons in insulating materials to be excited across the band gap, and in graphene to be promoted from the lower to the upper Dirac cone.…”

“…Optical pumping causes electrons in insulating materials to be excited across the band gap, and in graphene to be promoted from the lower to the upper Dirac cone. These hot electrons (and holes) then thermalize via carrier-carrier interactions to reach a Fermi-Dirac distribution in the conduction and valence bands within ∼10's fs, reaching attainable electronic temperatures of thousands of degrees [9,[17][18][19][20], and eventually relaxing to the atomic lattice temperature, with a minor overall temperature increase due to the high heat capacity of the lattice compared with electrons. Timeand angle-resolved photoemission spectroscopy (TR-ARPES) has corroborated this picture by monitoring the formation of Fermi-Dirac distributions of electrons and holes after ∼10's fs following optical pumping [21][22][23][24][25].…”

Black Phosphorus/Platinum Heterostructure: A Highly Efficient Photocatalyst for Solar‐Driven Chemical Reactions

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natural resource depletion, pollution, and possible global warming. [10][11][12][13][14] The layer-dependent direct bandgap ranging between 0.3 and 2.0 eV makes BP a promising absorber of broad solar light extending into the infrared region. [4][5][6] To fully utilize solar energy in chemical production, there are three goals for photocatalysts: robust harvesting of solar light spanning a broad spectrum, high charge separation and migration to the catalyst surface, and effective coupling of the photogenerated carrier into chemical reactions.

Black phosphorus (BP), an emerging 2D semiconductor with a narrow bandgap and high charge carrier mobility, [7][8][9] has attracted a great deal of attention in electronics and optoelectronics.

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