Experimental evidence of rainbow trapping and Bloch oscillations of torsional waves in chirped metallic beams

[EN] The Bloch oscillations (BO) and the rainbow trapping (RT) are two apparently unrelated phenomena, the former arising in solid state physics and the latter in metamaterials. A Bloch oscillation, on the one hand, is a counter-intuitive effect in which electrons start to oscillate in a crystalline structure when a static electric field is applied. This effect has been observed not only in solid state physics but also in optical and acoustical structured systems since a static electric field can be mimicked by a chirped structure. The RT, on the other hand, is a phenomenon in which the speed of a wave packet is slowed down in a dielectric structure; different colors then arrive to different depths within the structure thus separating the colors also in time. Here we show experimentally the emergence of both phenomena studying the propagation of torsional waves in chirped metallic beams. Experiments are performed in three aluminum beams in which different structures were machined: one periodic and two chirped. For the smaller value of the chirping parameter the wave packets, with different central frequencies, are back-scattered at different positions inside the corrugated beam; the packets with higher central frequencies being the ones with larger penetration depths. This behavior represents the mechanical analogue of the rainbow trapping effect. This phenomenon is the precursor of the mechanical Bloch oscillations, which are here demonstrated for a larger value of the chirping parameter. It is observed that the oscillatory behavior observed at small values of the chirp parameter is rectified according to the penetration length of the wave packet.Work partially supported by DGAPA-UNAM under projects PAPIIT IN103115 and IN109318 and by CONACYT project 284096. A.A.L. acknowledges CONACYT for the support granted to pursue his Ph.D. studies. G. Baez received CONACYT's financial support. RAMS received support from DGAPA-UNAM under program PASPA. We thank M. Martinez, A. Martinez, V. Dominguez-Rocha, E. Flores and E. Sadurni for invaluable comments. F.C., A.C. and J.S-D. acknowledge the support by the Ministerio de Economa y Competitividad of the Spanish government, and the European Union FEDER through project TEC2014-53088-C3-1-R.Arreola-Lucas, A.; Baez, G.; Cervera Moreno, FS.; Climente Alarcón, A.; Mendez-Sanchez, R.; Sánchez-Dehesa Moreno-Cid, J. (2019). Experimental evidence of rainbow trapping and Bloch oscillations of torsional waves in chirped metallic beams. Scientific Reports. 9:1860-1872. https://doi.org/10.1038/s41598-018-37842-7S186018729Ascroft, N. W. & Mermin, N. D. Solid State Physics (Hold, Reinhart & Winston, 1972).Kadic, M., Buckmann, T., Schittny, R. & Wegener, M. Metamaterials beyond electromagnetism. Rep. Prog. Phys. 76, 126501 (2013).Cummer, S. A., Christensen, J. & Alù, A. 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ALaMn(2)O(6-y) (A=K, Rb): Novel ferromagnetic manganites exhibiting negative giant magnetoresistance

We report the synthesis of a new series of manganese oxides, ALaMn(2)O(6-y), for A = K, nb, and Cs, that adopt an ordered superstructure of the perovskite. The Ii and Rb phases are tetragonal (a(t) similar to 7.75, c(t) similar to 7.10 Angstrom) and the Cs phase is orthorhombic (a(0) = 5.511, b(0) = 5.468, c = 7.311 Angstrom) indicating 2a(p) x 2a(p) and root 2a(p) x root 2a(p) x 2a(p) (a(p) = perovskite subcell) superstructures, respectively. The K and Rb phases are ferromagnetic (T-c similar to 327 and 300 K) metals, exhibiting a giant magnetoresistance behavior similar to alkaline earth metal substituted lanthanide manganites. The results reveal that it is possible to induce Mn(III)I Mn(TV) mixed valency and the related electronic properties through action deficiency in ordered perovskites of the kind ALaMn(2)O(6)

Metal-insulator transition in colossal magnetoresistance materials

We report on resistivity measurements in La0.67Ca0.33MnO3 and Nd0.7Sr0.3MnO3 thin films in order to elucidate the underlying mechanism for the colossal magnetoresistance behavior. The experimental results are analyzed in terms of quantum phase-transition ideas to study the nature of the metal-insulator transition in manganese oxides. Resistivity curves as functions of magnetization for various temperatures show the absence of scaling behavior expected in a continuous quantum phase transition, which leads us to conclude that the observed metal-insulator transition is most likely a finite temperature crossover phenomenon. ©2000 The American Physical Society.link_to_subscribed_fulltex

Rainbow trapping in a chirped three-dimensional photonic crystal

Light localization and intensity enhancement in a woodpile layer-by-layer photonic crystal, whose interlayer distance along the light propagation direction is gradually varied, has been theoretically predicted and experimentally demonstrated. The phenomenon is shown to be related to the progressive slowing down and stopping of the incident wave, as a result of the gradual variation of the local dispersion. The light localization is chromatically resolved, since every frequency component is stopped and reflected back at different positions along the crystal. It has been further discussed that the peculiar relation between the stopping position and the wave vector distribution can substantially increase the enhancement factor to more than two orders of magnitude. Compared to previously reported one-and two-dimensional photonic crystal configurations, the proposed scheme has the advantage of reducing the propagation losses by providing a three-dimensional photonic bandgap confinement in all directions. The slowing down and localization of waves inside photonic media can be exploited in optics and generally in wave dynamics, in many applications that require enhanced interaction of light and matter.Authors acknowledge financial support of NATO SPS research grant No: 985048. K.S. acknowledges financial support of Spanish Ministerio de Ciencia e Innovacion and European Union FEDER through project FIS2015-65998- C2-1-P. H.K. also acknowledges partial support of the Turkish Academy of Science