15 research outputs found
Dynamics of light-induced anomalous Hall effect in the three-dimensional Dirac semimetal CdAs
We experimentally study the dynamical behavior of the light-induced anomalous
Hall effect in a three-dimensional Dirac semimetal, CdAs. An
ultrashort, circularly polarized, multi-terahertz pump pulse breaks the
time-reversal symmetry of a thin film sample. The resulting anomalous Hall
effect is clearly observed through the polarization rotation of a single-cycle
terahertz probe pulse. Comparing the experimental result with theory, we find
that the field-induced injection current dominates the anomalous Hall effect
during pump irradiation, while the Berry curvature of the Floquet-Weyl
semimetal state does not appreciably contribute. Remarkably, even after pump
irradiation, we observe an anomalous Hall effect that lasts for more than 10
ps. A model fit to the Hall conductivity spectrum reveals a relatively long
scattering time over 400 fs. This result shows that circularly polarized light
creates a polarization of the isospin degree of freedom in the Dirac semimetal,
which labels the crystallographic point group representation of the overlapping
Weyl semimetal bands. Our observation paves the way for conversion of a robust
isospin flow into an electric current at room temperature, being a new analogue
of the inverse spin Hall effect.Comment: 44 pages, 14 figure
Terahertz field-induced ionization and perturbed free induction decay of excitons in bulk GaAs
We investigated the interaction between an intense terahertz (THz) pulse and excitons in bulk GaAs by using THz pump near-infrared (NIR) optical probe spectroscopy. We observed a clear spectral oscillation in the NIR transient absorption spectra at low temperature, which is interpreted as the THz pump-induced perturbed free induction decay (PFID) of the excitonic interband polarization. We performed a numerical simulation based on a microscopic theory and identified that the observed PFID signal originates from the THz field-induced ionization of excitons. Using a real-space representation of the excitonic wave function, we visualized how the ionization of an exciton proceeds under the intense single-cycle THz electric field. We also calculated the nonlinear susceptibility with the lowest-order perturbation theory assuming a weak THz pump, which showed a similar spectral feature with that obtained by the full treatment to field-induced ionization process. This coincidence is attributed to the fact that 1s-excitonic interband polarization is modified predominantly through interactions with the p-wave component of the excitonic wave function. A simple phenomenological expression of the PFID signal is presented to discuss effects of the THz pump pulse duration on the spectral oscillation
Time-domain characterization of electric field vector in multi-terahertz pulses using polarization-modulated electro-optic sampling
We demonstrated characterizing the electric field waveform of multi-terahertz pulses (10-50 THz) as vector quantities in the time domain by applying the polarization modulated electro-optic sampling (POMEOS) method. The problem of an ultrabroadband gate pulse was solved by modifying the fitting function in POMEOS and its validity was confirmed through numerical simulations. High accuracy and precision of approximately 1 mrad with 3 s accumulation were demonstrated. Our method can be applied not only to multi-terahertz polarization measurements for linear response but also to the evaluation of the driving field of intense pulses for nonlinear response or material control
Theory of light-induced resonances with collective Higgs and Leggett modes in multiband superconductors
Observation of Terahertz Spin Hall Conductivity Spectrum in GaAs with Optical Spin Injection
We report the first observation of the spin Hall conductivity spectrum in
GaAs at room temperature. After the optical injection of spin-polarized
carriers, polarization rotation of a terahertz pulse is observed as a
manifestation of the inverse spin Hall effect. The spectrum for the spin Hall
conductivity of electrons exhibits an excellent agreement with microscopic
theories only using known parameters. The results clearly demonstrate that,
unlike in the DC regime, the intrinsic Berry-curvature mechanism is dominant in
terahertz frequency, enabling high-speed less-dissipative charge-spin current
conversion.Comment: 18 pages, 4 figure
Distinct Metabolites for Photoreactive L-Phenylalanine Derivatives in Klebsiella sp. CK6 Isolated from Rhizosphere of a Wild Dipterocarp Sapling
molecule