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A facile chemical vapor deposition method to prepare single-crystalline VS2 nanosheets for the hydrogen evolution reaction is reported. The electrocatalytic hydrogen evolution reaction (HER) activities of VS2 show an extremely low overpotential of -68 mV at 10 mA cm(-2), small Tafel slopes of ≈34 mV decade(-1), as well as high stability, demonstrating its potential as a candidate non-noble-metal catalyst for the HER.

Plasmonic nanostructures have been proposed as useful materials for photon harvesting applications. However, the mechanisms by which energy transfer occurs across interfaces formed between plasmonic materials and their environment are under debate. A commonly invoked mechanism is indirect hot charge carrier transfer, where hot carriers are generated in the plasmonic material by nonradiatve plasmon decay, followed by transfer of these carriers to interfacial species in a sequential process. Alternatively, chemical interface damping has been reported to allow direct interaction between surface plasmons and interfacial species electronic states. Here we provide evidence from experiment and theory that for plasmon-mediated catalytic O 2 dissociation on Ag plasmonic nanoparticles, the direct interaction of O 2 molecules with surface plasmon near-fields was responsible for observed photocatalysis. These results offer important mechanistic insights for the design of plasmonic materials that maximize efficiency for promoting catalytic small molecule activation using photon fluxes.

Nonperturbative coupling of light with condensed matter in an optical cavity is expected to reveal a host of coherent many-body phenomena and states [1][2][3][4][5][6][7]. In addition, strong coherent light-matter interaction in a solid-state environment is of great interest to emerging quantum-based technologies [8,9]. However, creating a system that combines a long electronic coherence time, a large dipole moment, and a high cavity quality (Q) factor has been a challenging goal [10][11][12][13]. Here, we report collective ultrastrong light-matter coupling in an ultrahigh-mobility two-dimensional electron gas in a high-Q terahertz photonic-crystal cavity in a quantizing magnetic field, demonstrating a cooperativity of ∼360. The splitting of cyclotron resonance (CR) into the lower and upper polariton branches exhibited a √ ne-dependence on the electron density (ne), a hallmark of collective vacuum Rabi splitting. Furthermore, a small but definite blue shift was observed for the polariton frequencies due to the normally negligible A 2 term in the light-matter interaction Hamiltonian. Finally, the high-Q cavity suppressed the superradiant decay of coherent CR, which resulted in an unprecedentedly narrow intrinsic CR linewidth of 5.6 GHz at 2 K. These results open up a variety of new possibilities to combine the traditional disciplines of many-body condensed matter physics and cavity-based quantum optics.PACS numbers: 78.67. De, 76.40.+b, 78.47.jh Strong resonant light-matter coupling in a cavity setting is an essential ingredient in fundamental cavity quantum electrodynamics (QED) studies [14] as well as in cavity-QED-based quantum information processing [8,9]. In particular, a variety of solid-state cavity QED systems have recently been examined [15][16][17][18], not only for the purpose of developing scalable quantum technologies, but also for exploring novel many-body effects inherent to condensed matter. For example, collective √ N -fold enhancement of light-matter coupling in an N -body system [19], combined with colossal dipole moments available in solids, compared to traditional atomic systems, is promising for entering uncharted regimes of ultrastrong light-matter coupling. Nonintuitive quantum phenomena can occur in such regimes, including a "squeezed" vacuum state [1], the Dicke superradiant phase transition [2,3], the breakdown of the Purcell effect [4], and quantum vacuum radiation [5] induced by the dynamic Casimir effect [6,7].Specifically, in a cavity QED system, there are three rates that jointly characterize different light-matter coupling regimes: g, κ, and γ. The parameter g is the coupling constant, with 2g being the vacuum Rabi splitting between the two normal modes, the lower polariton (LP) and upper polariton (UP), of the coupled system. The parameter κ is the photon decay rate of the cavity; τ cav = κ −1 is the photon lifetime of the cavity, and the cavity Q = ω 0 τ cav at mode frequency ω 0 . The parameter γ is the nonresonant matter decay rate, which is usually the decoherence rate in ...

A two-level system resonantly interacting with an ac magnetic or electric field constitutes the physical basis of diverse phenomena and technologies. However, Schrödinger's equation for this seemingly simple system can be solved exactly only under the rotating wave approximation, which neglects the counter-rotating field component. When the ac field is sufficiently strong, this approximation fails, leading to a resonance-frequency shift known as the Bloch-Siegert (BS) shift. Here, we report the vacuum BS shift, which is induced by the ultrastrong coupling of matter with the counter-rotating component of the vacuum fluctuation field in a cavity. Specifically, an ultra-high-mobility 2D electron gas inside a high-Q terahertz cavity in a quantising magnetic field revealed ultra-narrow Landau polaritons, which exhibited a vacuum BS shift up to 40 GHz. This shift, clearly distinguishable from the photon-field selfinteraction effect, represents a unique manifestation of a strong-field phenomenon without a strong field. sions. We thank Yoichi Kawada, Hironori Takahashi, and Hamamatsu Photonics K.K. for fabricating the achromatic THz quarter wave plate. J.K.

Of the many plasmonic nanoparticle geometries that have been synthesized, nanocubes have been of particular interest for creating nanocavities, facilitating plasmon coupling, and enhancing phenomena dependent upon local electromagnetic fields. Here we report the straightforward colloidal synthesis of single-crystalline {100} terminated Al nanocubes by decomposing AlH3 with Tebbe’s reagent in tetrahydrofuran. The size and shape of the Al nanocubes is controlled by the reaction time and the ratio of AlH3 to Tebbe’s reagent, which, together with reaction temperature, establish kinetic control over Al nanocube growth. Al nanocubes possess strong localized field enhancements at their sharp corners and resonances highly amenable to coupling with metallic substrates. Their native oxide surface renders them extremely air stable. Chemically synthesized Al nanocubes provide an earth-abundant alternative to noble metal nanocubes for plasmonics and nanophotonics applications.

Catalysts based on platinum group metals have been a major focus of the chemical industry for decades. We show that plasmonic photocatalysis can transform a thermally unreactive, earth-abundant transition metal into a catalytically active site under illumination. Fe active sites in a Cu-Fe antenna-reactor complex achieve efficiencies very similar to Ru for the photocatalytic decomposition of ammonia under ultrafast pulsed illumination. When illuminated with light-emitting diodes rather than lasers, the photocatalytic efficiencies remain comparable, even when the scale of reaction increases by nearly three orders of magnitude. This result demonstrates the potential for highly efficient, electrically driven production of hydrogen from an ammonia carrier with earth-abundant transition metals.

Al nanocrystals can be synthesized by high-temperature decomposition of triisobutyl aluminum, creating a mixture of nanoparticle geometries with a significant fraction (∼15%) being single-crystalline Al nanorods. The Al nanorods are elongated along their ⟨110⟩ direction, and generally exhibit hexagonal cross sections consisting of two adjacent {111} facets separated by {100} facets on opposite sides. Dark-field scattering spectroscopy of individual Al nanorods reveals that rods of varying aspect ratios all possess transverse quadrupolar and octupolar modes in the visible (2-3 eV) and ultraviolet (3-5 eV) regimes. Theoretical modeling indicates that the longitudinal resonances of these nanorods span the near- and mid-infrared regions of the spectrum. This work introduces a new class of anisotropic metal nanocrystals composed of single-crystalline Al, opening the door to highly modifiable plasmonic nanorods from Earth-abundant metals.