We study the nonlinear propagation of femtosecond pulses in the anomalous dispersion region of microstructured fibers, where soliton fission mechanisms play an important role. The experiment shows that the output spectrum contains, besides the infrared supercontinuum, a narrow-band 430-nm peak, carrying about one fourth of the input energy. By combining simulation and experiments, we explore the generation mechanism of the visible peak and describe its properties. The simulation demonstrates that the blue peak is generated only when the input pulse is so strongly compressed that the short-wavelength tail of the spectrum includes the wavelength predicted for the dispersive wave. In agreement with simulation, intensity-autocorrelation measurements show that the duration of the blue pulse is in the picosecond time range, and that, by increasing the input intensity, satellite pulses of lower intensity are generated.

Recent progresses in the second generation REBa 2 Cu 3 O 7 − x (RE123) coated conductor (CC) have paved a way for the development of superconducting solenoids capable of generating fields well above 23.5 T, i.e. the limit of NbTi−Nb 3 Sn-based magnets. However, the RE123 magnet still poses several fundamental and engineering challenges. In this work we review the state-ofthe-art of conductor and magnet technologies. The goal is to illustrate a close synergetic relationship between evolution of high-field magnets and advancement in superconductor technology. The paper is organized in three parts: (1) the basics of RE123 CC fabrication technique, including latest developments to improve conductor performance and production throughput; (2) critical issues and innovative design concepts for the RE123-based magnet; and (3) an overview of noteworthy ongoing magnet projects.

We present a detailed optical study of single-crystal bismuth using infrared reflectivity and ellipsometry. Large changes in the plasmon frequency are observed as a function of temperature due to charge transfer between hole and electron Fermi pockets. In the optical conductivity, an anomalous temperature dependent midinfrared absorption feature is observed. An extended Drude model analysis reveals that it can be connected to a sharp upturn in the scattering rate, the frequency of which exactly tracks the temperature dependent plasmon frequency. We interpret this absorption and increased scattering as direct optical evidence for a charge carrier interaction with a collective mode of purely electronic origin, here electron-plasmon scattering. The observation of a plasmaron as such is made possible only by the unique coincidence of various energy scales and exceptional properties of semimetal bismuth. DOI: 10.1103/PhysRevLett.99.016406 PACS numbers: 71.45.ÿd, 78.20.ÿe, 78.30.ÿj, 78.40.Kc Elemental semimetals, such as graphite and bismuth, are materials of much long term interest due to their exceptional properties, including large magnetoresistive and pressure dependent effects [1][2][3]. In the case of bismuth, these properties derive from its low carrier number ( 10 ÿ5 electrons per atom), reduced effective masses ( 10 ÿ2 electron masses), small Fermi wave vector ( 40 nm), and long mean free path ( 0:1 mm).A number of recent results are causing an increased interest in these materials, both from the side of fundamental solid-state physics as well as applications potential. For instance, field dependent crossovers reminiscent of a metal-insulator transition have been observed in both graphite and bismuth [4,5]. Isolated single layers of graphene have been shown to have novel transport properties and an anomalous quantization of the quantum Hall effect resulting from their exceptional zero mass Dirac cone dispersion relation [6,7]. Moreover, there continues to be interest in bismuth for quantum confinement studies [8]. On the technical side, advances in film growth [9], anomalously long spin diffusion lengths, and very large magnetoresistive response make bismuth useful for possible incorporation in nanomagnetometers, magnetooptical devices, and spintronics applications [10,11].In principle, transport phenomena in bismuth should be well described by the conventional metals theory, but due to the exceptionally low Fermi energy, effective masses and charge densities there are substantial departures from standard metallic behavior. Moreover, the material's very low carrier density opens up the possibility for novel plasmonic effects and strong electron-electron interactions due to the relative scales between potential and kinetic energy at low charge densities [12].In this Letter, we present detailed temperature dependent optical measurements over the full optical range from farinfrared (FIR) to UVof single-crystal bismuth. We observe a narrow Drude peak and a plasmon energy consistent with the low carrier number...

The application of pressure to elemental bismuth reduces its conduction-valence band overlap, and results in a semimetal-semiconductor (SMSC) transition around 25 kbar. This transition is nominally of the topological ''Lifshitz'' Fermi surface variety, but there are open questions about the role of interactions at low charge densities. Using a novel pressure cell with optical access, we have performed an extensive study of bismuth's infrared conductivity under pressure. In contrast to the expected pure band behavior we find signatures of enhanced interaction effects, including strongly coupled charge-plasmon (plasmaron) features and a plasma frequency that remains finite up to the transition. These effect are inconsistent with a pure Lifshitz bandlike transition. We postulate that interactions play a central role in driving the transition.

The effect of dimensionality on materials properties has become strikingly evident with the recent discovery of graphene. Charge ordering phenomena can be induced in one dimension by periodic distortions of a material's crystal structure, termed Peierls ordering transition. Charge-density waves can also be induced in solids by strong coulomb repulsion between carriers, and at the extreme limit, Wigner predicted that crystallization itself can be induced in an electrons gas in free space close to the absolute zero of temperature. Similar phenomena are observed also in higher dimensions, but the microscopic description of the corresponding phase transition is often controversial, and remains an open field of research for fundamental physics. Here, we photoinduce the melting of the charge ordering in a complex three-dimensional solid and monitor the consequent charge redistribution by probing the optical response over a broad spectral range with ultrashort laser pulses. Although the photoinduced electronic temperature far exceeds the critical value, the charge-density wave is preserved until the lattice is sufficiently distorted to induce the phase transition. Combining this result with ab initio electronic structure calculations, we identified the Peierls origin of multiple charge-density waves in a three-dimensional system for the first time.ultrafast broadband spectroscopy | electron-lattice interactions | optical spectral weight C harge ordering phenomena occurring upon symmetry breaking are important in solids as they give rise to current and spin flow patterns in promising materials such as organic conductors (1), multilayered graphene (2) and transition metal oxides (3). The possibility to investigate the microscopic steps through which such ordering transition occurs also gives the opportunity to speculate on more general aspects of critical phenomena. Chargedensity waves (CDWs) (4, 5), sandpile automata (6), and Josephson arrays (7) have been investigated in relation to the scale invariance of self-organized critical phenomena (8), of which avalanches are dramatic manifestations (9). In one dimension, Peierls demonstrated that at low temperature an instability can be induced by the coupling between carriers and a periodic lattice distortion. Such an instability triggers a charge ordering phenomenon and a metal-insulator phase transition, called Peierls transition, occurs (10). Like for Bardeen-Cooper-Schrieffer (BCS) superconductors, such an electron-phonon interaction-driven transition is expected to be second order (10). Although this situation is fairly established in monodimensional organic materials (11), increased hybridization leading to higher dimensionality of a solid perturbs this scenario and makes the assessment of the microscopic origin of charge localization phenomena more difficult (12)(13)(14).Contrary to other low-dimensional CDW (15) systems studied so far by time-resolved spectroscopies (16-19), Lu 5 Ir 4 Si 10 presents a complex three-dimensional structure with several substructures suc...