Surface plasmons are collective oscillations of electrons in metals or semiconductors that enable confinement and control of electromagnetic energy at sub wavelength scales. Rapid progress in plasmonics has largely relied on advances in device nano-fabrication, whereas less attention has been paid to the tunable properties of plasmonic media. One such medium—graphene—is amenable to convenient tuning of its electronic and optical properties by varying the applied voltage. Here, using infrared nano-imaging, we show that common graphene/SiO2/Si back-gated structures support propagating surface plasmons. The wavelength of graphene plasmons is of the order of 200 nanometres at technologically relevant infrared frequencies, and they can propagate several times this distance. Link

We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac fermions in graphene. This is achieved by confining mid-IR radiation at the apex of a nanoscale tip: an approach yielding 2 orders of magnitude increase in the value of in-plane component of incident wavevector qcompared to free space propagation. At these high wavevectors, the Dirac plasmon is found to dramatically enhance the near-field interaction with mid-IR surface phonons of SiO2 substrate. Our data augmented by detailed modeling establish graphene as a new medium supporting plasmonic effects that can be controlled by gate voltage. Link

Our imaging technique, which we refer to as „scanning plasmon interferometery‟, is implemented in a setting of an antenna-based infrared (IR) nanoscope6-8 . A schematic diagram of the scanning plasmon interferometry technique is shown in Fig. 1a. Infrared light focused on a metalized tip of an atomic force microscope (AFM) generates a strong localized field around the sharp tip apex, analogous to a “lightning-rod” effect . This concentrated electric field launches circular SPs around the tip (pink circles in the figure on the left). The process is controlled by two experimental parameters: the wavelength of light IR and the curvature radius of the tip R. In order to efficiently launch SPs on our highly doped graphene films, we chose IR light with IR close to 10 m and AFM tips with R ≈ 25 nm (Methods). The experimental observable of the scanning plasmon interferometry is the scattering amplitude s that is collected simultaneously with AFM topography. Link

We analyze the results of scanning near-field infrared spectroscopy performed on thin films of a-SiO 2 on Si substrate. The measured near-field signal exhibits surface-phonon resonances whose strength has a prominent thickness dependence in the range from 2 to 300 nm. These observations are compared with calculations in which the tip of the near-field infrared spectrometer is modeled either as a point dipole or an elongated spheroid. The latter model accounts for the antenna effect of the tip and gives a better agreement with the experiment. Possible applications of the near-field technique for depth profiling of layered nanostructures are discussed. Link

Near-field infrared spectroscopy has recently been demonstrated with the ability to resolve optical properties of sub-wavelength sample areas across a broad range of infrared frequencies [1]. This method holds promise for the direct identification of sub-wavelength chemical composition in nanostructured and heterogeneous samples. We apply this technique to the study of phonon-resonant silicon carbide nanocrystals and silicate nanospheres tens of nanometers in size using a scattering mode scanning near-field optical microscope (s-SNOM) coupled to a pulsed broadband infrared laser source and FTIR spectrometer. Measurements of nanocrystal near-field spectra in the range of 700-1300 cm− 1 are obtained with this technique and evaluated in comparison with nearfield spectra of bulk silicate and silicon carbide. Material properties are calibrated with ellipsometry, X-ray … Link

We report on the first implementation of ultrafast near field measurements carried out with the transient pseudoheterodyne detection method (Tr-pHD). This method is well suited for efficient and artifact free pump-probe scattering-type near-field optical microscopy with nanometer scale resolution. The Tr-pHD technique is critically compared to other data acquisition methods and found to offer significant advantages. Experimental evidence for the advantages of Tr-pHD is provided in the near-IR frequency range. Crucial factors involved in achieving proper performance of the Tr-pHD method with pulsed laser sources are analyzed and detailed in this work. We applied this novel method to femtosecond time-resolved and nanometer spatially resolved studies of the photo-induced effects in the insulator-to-metal transition system vanadium dioxide. Link

All known superfluid and superconducting states of condensed matter are enabled by composite bosons (atoms, molecules and Cooper pairs) made of an even number of fermions. Temperatures where such macroscopic quantum phenomena occur are limited by the lesser of the binding energy and the degeneracy temperature of the bosons. High-critical temperature cuprate superconductors set the present record of~ 100 K. Here we propose a design for artificially structured materials to rival this record. The main elements of the structure are two monolayers of a transition metal dichalcogenide separated by an atomically thin spacer. Electrons and holes generated in the system would accumulate in the opposite monolayers and form bosonic bound states—the indirect excitons. The resultant degenerate Bose gas of indirect excitons would exhibit macroscopic occupation of a … Link

We report on the observation of the Pancharatnam-Berry phase in a condensate of indirect excitons realized in a GaAs coupled quantum well structure. Our measurements indicate long range coherent spin transport … The Pancharatnam-Berry phase is a geometric phase acquired over a cycle of parameters in the Hamiltonian gov- erning the evolution of the system. It was discovered by Pancharatnam in studies of polarized light and introduced by Berry as a topological phase for matter wave functions. Excitons are matter waves that directly transform to photons inheriting their coherence … Link

If bosonic particles are cooled down below the temperature of quantum degeneracy, they can spontaneously form a coherent state in which individual matter waves synchronize and combine. Spontaneous coherence of matter waves forms the basis of a number of fundamental phenomena in physics, including superconductivity, superfluidity and Bose– Einstein condensation 1, 2. Spontaneous coherence is the key characteristic of condensation in momentum space 3. Excitons—bound pairs of electrons and holes—form a model system to explore the quantum physics of cold bosons in solids 4, 5. Cold exciton gases can be realized in a system of indirect excitons, which can cool down below the temperature of quantum degeneracy owing to their long lifetimes 6. Here we report measurements of spontaneous coherence in a gas of indirect excitons. We found that … Link