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Using intense, few-cycle THz pulses we investigate the strong-field interaction with polarons in La0.7Ca0.3MnO3. By probing the optical reflectivity, we observe a THz-induced detrapping of electrons from polarons, followed by thermalization of phonons with spins.
We perform experimental characterization of switchable THz metasurfaces using variable-angle broadband THz ellipsometry. We extract frequency dependent surface susceptibility tensors and model the applied DC bias as tuning the conductivity of the active layer.
We present an electrically modulated nonlinear metamaterial at terahertz frequencies. The device consists of a planar array of split-ring resonators (SRRs) fabricated on n-type GaAs. Increasing the incident THz field strength induces carriers in the GaAs substrate, shorting the SRR capacitive gap and modulating the MM resonance. The application of a 15V bias to the MM reduces the net field modulation...
Ultrafast optical spectroscopy reveals surface-bulk scattering in the Weyl semimetal NbAs within 50 femtoseconds. The direction of this scattering can be controlled by the pump and probe polarizations, suggesting potential ultrafast device applications.
We describe experimental measurements and simulations of a switchable THz metasurface device in a slab waveguide geometry. The device exhibits giant phase modulation of the TE1 mode at particular frequencies determined by the metamaterial geometry. Simulations predict that a 2π phase shift can be realized in an interaction length of only a few millimeters.
We demonstrate a powerful, table-top approach for directly visualizing crystal lattice dynamics using optical second harmonic generation after intense terahertz photoexcitation of a specific phonon mode in the topological insulator Bi2Se3.
We used optical-pump, terahertz-probe spectroscopy to track carrier dynamics in a two-dimensional electron gas under a magnetic field, revealing photoinduced changes to the cyclotron frequency and scattering time, along with an unexpected higher frequency mode.
We present an electrically modulated nonlinear metamaterial at terahertz frequencies. The device consists of a planar array of split-ring resonators (SRRs) fabricated on n-type GaAs. Increasing the incident THz field strength induces carriers in the GaAs substrate, shorting the SRR capacitive gap and modulating the MM resonance. The application of a 15V bias to the MM reduces the net field modulation...
We describe experimental characterization of switchable THz metasurfaces using variable-angle broadband THz ellipsometry. A theoretical framework is used to extract surface susceptibility tensors as a function of frequency and applied DC bias. This will allow us to make a priori predictions of the performance of these devices for applications as metasurface active components.
We have used ultrafast THz spectroscopy to both excite and probe low energy excitations in two-dimensional electron gases, topological insulators, and multiferroics.
We describe experimental characterization of switchable terahertz metasurfaces using broadband ellipsometry. A theoretical framework based on generalized sheet transition conditions is developed to extract surface susceptibility as a function of frequency and applied DC bias. This will allow us to make a priori predictions of the performance of these switchable devices in device applications, enabling...
Hexagonal LuFeO3 is a multiferroic showing ferroelectricity and antiferromagnetism at room temperature. Below TR=130 K, it becomes ferrimagnetic. Ultrafast optical pump-probe measurements reveal that the dynamics are correlated with the structural changes responsible for ferrimagnetism.
We directly resolve energy transfer pathways from electrons to magnons in multiferroic HoMnO3 using ultrafast optical/terahertz spectroscopy. This reveals that energy is initially transferred from electrons to phonons and subsequently to magnons through spin-lattice relaxation.
Terahertz magneto-optical spectroscopy on a two-dimensional hole gas reveal a nonlinear dependence on the applied magnetic field. This is due to its complex non-parabolic valence band structure, as verified by multiband Landau level theoretical calculations.
We experimentally and numerically investigate a switchable dielectric-slab-waveguide metasurface device. We use an active metasurface to manipulate the interaction with a propagating THz surface wave, giving us dynamic control of the wave at 0.3 THz.
Topological insulators represent a new state of matter where bulk insulators exhibit metallic surfaces that are protected by time reversal symmetry. However, in common transport measurements residual bulk conductivity hinders the properties of the topologically protected surfaces. Alternatively, terahertz spectroscopy has recently been shown to be capable of discerning the bulk and surface carrier...
We design and test a switchable diffraction grating based on active metamaterials for terahertz modulation. We observe off-axis diffraction which permits operation of the device as a high-contrast modulator, with better than 20 dB of dynamic range.
Ultrafast optical pump-probe spectroscopy is used to study a heterostructure consisting of superconducting and antiferromagnetic films. We observed a new slow relaxation process that reveals the interaction between superconducting and antiferromagnetic order at the interface.
We design and test a switchable diffraction grating based on active metamaterials for terahertz modulation. We observe off-axis diffraction which permits operation of the device as a narrowband high-contrast modulator.
Terahertz time-domain spectroscopy and temperature dependent femtosecond optical pump-probe spectroscopy are used to track quasiparticle dynamics at the interface between superconducting and ferromagnetic oxide layers.
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