355 research outputs found
Terahertz signatures of ultrafast Dirac fermion relaxation at the surface of topological insulators
Topologically protected surface states present rich physics and promising spintronic, optoelectronic, and photonic applications that require a proper understanding of their ultrafast carrier dynamics. Here, we investigate these dynamics in topological insulators (TIs) of the bismuth and antimony chalcogenide family, where we isolate the response of Dirac fermions at the surface from the response of bulk carriers by combining photoexcitation with below-bandgap terahertz (THz) photons and TI samples with varying Fermi level, including one sample with the Fermi level located within the bandgap. We identify distinctly faster relaxation of charge carriers in the topologically protected Dirac surface states (few hundred femtoseconds), compared to bulk carriers (few picoseconds). In agreement with such fast cooling dynamics, we observe THz harmonic generation without any saturation effects for increasing incident fields, unlike graphene which exhibits strong saturation. This opens up promising avenues for increased THz nonlinear conversion efficiencies, and high-bandwidth optoelectronic and spintronic information and communication applications.Parts of this research were carried out at ELBE at the Helmholtz-Zentrum Dresden-Rossendorf e.V., a member of the Helmholtz Association. The films are grown in IRE RAS within the framework of the state task. This work was supported by the RFBR grants Nos. 18-29-20101, 19-02-00598. N.A., S.K., and I.I. acknowledge support from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 737038 (TRANSPIRE). T.V.A.G.O. and L.M.E. acknowledge the support by the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter (ct.qmat). K.-J.T. acknowledges funding from the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 804349 (ERC StG CUHL) and financial support through the MAINZ Visiting Professorship. ICN2 was supported by the Severo Ochoa program from Spanish MINECO Grant No. SEV-2017-0706
Impulsive Fermi magnon-phonon resonance in antiferromagnetic
Understanding spin-lattice interactions in antiferromagnets is one of the
most fundamental issues at the core of the recently emerging and booming fields
of antiferromagnetic spintronics and magnonics. Recently, coherent nonlinear
spin-lattice coupling was discovered in an antiferromagnet which opened the
possibility to control the nonlinear coupling strength and thus showing a novel
pathway to coherently control magnon-phonon dynamics. Here, utilizing intense
narrow band terahertz (THz) pulses and tunable magnetic fields up to 7 T, we
experimentally realize the conditions of the Fermi magnon-phonon resonance in
antiferromagnetic . These conditions imply that both the spin and the
lattice anharmonicities harvest energy transfer between the subsystems, if the
magnon eigenfrequency is twice lower than the frequency of the phonon
. Performing THz pump-infrared probe spectroscopy in conjunction
with simulations, we explore the coupled magnon-phonon dynamics in the vicinity
of the Fermi-resonance and reveal the corresponding fingerprints of an
impulsive THz-induced response. This study focuses on the role of nonlinearity
in spin-lattice interactions, providing insights into the control of coherent
magnon-phonon energy exchange
Tunable room temperature nonlinear Hall effect from the surfaces of elementary bismuth thin films
The nonlinear Hall effect (NLHE) with time-reversal symmetry constitutes the
appearance of a transverse voltage quadratic in the applied electric field. It
is a second-order electronic transport phenomenon that induces frequency
doubling and occurs in non-centrosymmetric crystals with large Berry curvature
-- an emergent magnetic field encoding the geometric properties of electronic
wavefunctions. The design of (opto)electronic devices based on the NLHE is
however hindered by the fact that this nonlinear effect typically appears at
low temperatures and in complex compounds characterized by Dirac or Weyl
electrons. Here, we show a strong room temperature NLHE in the centrosymmetric
elemental material bismuth synthesized in the form of technologically relevant
polycrystalline thin films. The () surface electrons of this material
are equipped with a Berry curvature triple that activates side jumps and skew
scatterings generating nonlinear transverse currents. We also report a boost of
the zero field nonlinear transverse voltage in arc-shaped bismuth stripes due
to an extrinsic geometric classical counterpart of the NLHE. This electrical
frequency doubling in curved geometries is then extended to optical second
harmonic generation in the terahertz (THz) spectral range. The strong nonlinear
electrodynamical responses of the surface states are further demonstrated by a
concomitant highly efficient THz third harmonic generation which we achieve in
a broad range of frequencies in Bi and Bi-based heterostructures. Combined with
the possibility of growth on CMOS-compatible and mechanically flexible
substrates, these results highlight the potential of Bi thin films for THz
(opto)electronic applications.Comment: 44 pages, 21 figure
Nanoscale-confined Terahertz Polaritons in a van der Waals Crystal
Electromagnetic field confinement is crucial for nanophotonic technologies,
since it allows for enhancing light-matter interactions, thus enabling light
manipulation in deep sub-wavelength scales. In the terahertz (THz) spectral
range, radiation confinement is conventionally achieved with specially designed
metallic structures - such as antennas or nanoslits - with large footprints due
to the rather long wavelengths of THz radiation. In this context, phonon
polaritons - light coupled to lattice vibrations - in van der Waals (vdW)
crystals have emerged as a promising solution for controlling light beyond the
diffraction limit, as they feature extreme field confinements and low optical
losses. However, experimental demonstration of nanoscale-confined phonon
polaritons at THz frequencies has so far remained elusive. Here, we provide it
by employing scattering-type scanning near-field optical microscopy (s-SNOM)
combined with a free-electron laser (FEL) to reveal a range of low-loss
polaritonic excitations at frequencies from 8 to 12 THz in the vdW
semiconductor . We visualize THz polaritons with i) in-plane
hyperbolic dispersion, ii) extreme nanoscale field confinement (below
) and iii) long polariton lifetimes, with a lower limit of > 2
ps
Spin-orbit interaction driven terahertz nonlinear dynamics in transition metals
The interplay of electric charge, spin, and orbital polarizations, coherently
driven by picosecond long oscillations of light fields in spin-orbit coupled
systems, is the foundation of emerging terahertz spintronics and orbitronics.
The essential rules for how terahertz light interacts with these systems in a
nonlinear way are still not understood. In this work, we demonstrate a
universally applicable electronic nonlinearity originating from spin-orbit
interactions in conducting materials, wherein the interplay of light-induced
spin and orbital textures manifests. We utilized terahertz harmonic generation
spectroscopy to investigate the nonlinear dynamics over picosecond timescales
in various transition metal films. We found that the terahertz harmonic
generation efficiency scales with the spin Hall conductivity in the studied
films, while the phase takes two possible values (shifted by {\pi}), depending
on the d-shell filling. These findings elucidate the fundamental mechanisms
governing non-equilibrium spin and orbital polarization dynamics at terahertz
frequencies, which is relevant for potential applications of terahertz spin-
and orbital-based devices.Comment: 11 pages, 4 figure
Milliwatt terahertz harmonic generation from topological insulator metamaterials
Achieving efficient, high-power harmonic generation in the terahertz spectral
domain has technological applications, for example in sixth generation (6G)
communication networks. Massless Dirac fermions possess extremely large
terahertz nonlinear susceptibilities and harmonic conversion efficiencies.
However, the observed maximum generated harmonic power is limited, because of
saturation effects at increasing incident powers, as shown recently for
graphene. Here, we demonstrate room-temperature terahertz harmonic generation
in a BiSe topological insulator and topological-insulator-grating
metamaterial structures with surface-selective terahertz field enhancement. We
obtain a third-harmonic power approaching the milliwatt range for an incident
power of 75 mW - an improvement by two orders of magnitude compared to a
benchmarked graphene sample. We establish a framework in which this exceptional
performance is the result of thermodynamic harmonic generation by the massless
topological surface states, benefiting from ultrafast dissipation of electronic
heat via surface-bulk Coulomb interactions. These results are an important step
towards on-chip terahertz (opto)electronic applications
Distribuição de potássio em gotejamento com fertirrigação em diferentes pontos de injeção na linha principal
[EN] The purpose of this research was to evaluate the K2O distribution uniformity by surface drip irrigation at Universitat Politecnica de Valencia, Valencia, Spain (39º 29′ N, 0º 23′ W, 20 m). The irrigation was performed by drip lines with not-compensated emitters, spaced 0.3 m. The fertigation was realized using a fertilizer injector pump of electric action with injection of 0.25 h. The experimental design used completely randomized blocks with five treatments and four replications. The treatments consisted of injection in five distances, located at 10; 20; 30; 40; 50 m of the first drip line. Samples were collected in emitters located at the start, at 1/3, at 2/3 and at the end of the drip lines. The nutrient concentration was determined by flame spectrophotometry. The Christiansen's uniformity coefficients (CUC), of distribution (DUC), of statistical (SUC) and of emission (eUC) were estimated. The K2O concentration and distribution decreased linearly with the increase of the injection distance. In all treatments, the CUC, SUC and DUC were described as 'excellent'. The eUC was described as 'recommended' only at smaller injection distances.[PT] Objetivando fornecer subsídios para os produtores aperfeiçoarem o manejo da
fertirrigação em pequenas áreas, avaliou-se, na Universitat Politècnica de València, Valência,
Espanha (39° 29′ N, 0° 23′ W, 20 m), a uniformidade de distribuição do K2O via irrigação por
gotejamento superficial em função da distância do ponto de injeção na linha principal. A irrigação
foi efetuada por linhas laterais com emissores não compensantes, espaçados de 0,3 m. Na
fertirrigação, foi utilizada uma bomba injetora de fertilizante de acionamento elétrico, com o tempo
de injeção de 0,25 h. O delineamento experimental foi o de blocos casualizados, com cinco
tratamentos e quatro repetições. Os tratamentos consistiram em cinco pontos de injeção na linha
principal, situados a: 10; 20; 30; 40 e 50 m da primeira linha lateral. Foram coletadas amostras em
emissores localizados no início, a 1/3, a 2/3 e no final das linhas laterais. A concentração do
nutriente foi determinada por espectrofotometria de chama. Foram estimados os coeficientes de
uniformidade de Christiansen (CUC), de distribuição (CUD), estatístico (CUE) e de emissão (CUe).
A concentração e a distribuição de K2O diminuíram linearmente com o aumento da distância do
ponto de injeção. Em todos os tratamentos, o CUC, CUE e CUD foram classificados como
‘excelente’. O CUe foi classificado como ‘recomendado’ apenas na menor distância de injeção.To the Coordination of Improvement of Higher Education Personnel (CAPES) for grant the Doctoral Sandwich Abroad scholarship and the Universitat Politècnica de València (UPV), for providing the experimental area and all equipment and supplies needed for the research.Do Bomfim, GV.; Manzano Juarez, J.; De Azevedo, BM.; Vasconcelos, DV.; Viana, TVDA. (2014). Potassium distribution in drip irrigation with fertigation for different injection distances in the main line. Engenharia Agrícola. 34(6):1151-1161. doi:10.1590/S0100-69162014000600011S1151116134
Adubação potássica aplicada por fertirrigação e pelo método convencional na cultura do amendoim
Ultrafast Tunable Terahertz-to-Visible Light Conversion through Thermal Radiation from Graphene Metamaterials [Dataset]
6 pages. -- Supplementary Note 1, Sample Preparation. -- Supplementary Note 2, Experimental. -- Supplementary Note 3, Calculations of electron temperature. -- Supplementary Note 4, THz fluence and intensity. -- Supplementary Figures. -- Supplementary References.Several technologies, including photodetection, imaging, and data communication, could greatly benefit from the availability of fast and controllable conversion of terahertz (THz) light to visible light. Here, we demonstrate that the exceptional properties and dynamics of electronic heat in graphene allow for a THz-to-visible conversion, which is switchable at a sub-nanosecond time scale. We show a tunable on/off ratio of more than 30 for the emitted visible light, achieved through electrical gating using a gate voltage on the order of 1 V. We also demonstrate that a grating-graphene metamaterial leads to an increase in THz-induced emitted power in the visible range by 2 orders of magnitude. The experimental results are in agreement with a thermodynamic model that describes blackbody radiation from the electron system heated through intraband Drude absorption of THz light. These results provide a promising route toward novel functionalities of optoelectronic technologies in the THz regime.Peer reviewe
Gas exchange and leaf contents in bell pepper under energized water and biofertilizer doses
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