121 research outputs found
Lattice-Induced Double-Valley Degeneracy Lifting in Magnetic Field in Graphene
We show that the recently discovered double-valley splitting of the low-lying
Landau level(s) in the Quantum Hall Effect in graphene can be explained as
perturbative orbital interaction of intra- and inter-valley microscopic orbital
currents with a magnetic field. This effect is provided by the
translational-non-invariant terms corresponding to graphene's crystallographic
honeycomb symmetry but do not exist in the relativistic theory of massless
Dirac Fermions in Quantum Electrodynamics. We discuss recent data in view of
these results
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
Benzyne-mediated rearrangement of 3-(2-pyridyl)-1,2,4-triazines into 10-(1H-1,2,3-triazol-1-yl)pyrido[1,2-a]indoles
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
(Mechano)synthesis of azomethine- and terpyridine-linked diketopyrrolopyrrole-based polymers
Three efficient synthetic approaches towards new azomethine- and terpyridine-containing 2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (diketopyrrolopyrrole, DPP) based polymers, such as P1 and P2, are reported. The first approach involves the Pd-catalyzed synthesis via two- or three-component Suzuki or Stille cross-coupling reaction in solution. The second approach involves Pd-catalyzed Suzuki cross-coupling reaction under ball-milling conditions. And, finally, the third approach involves Pd-free condensation reaction under ball-milling conditions. The newly obtained polymers exhibited absorbance around 700 nm and emission around 900 nm, and, thus, these polymers are considered to be NIR-fluorophores
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
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