23 research outputs found
Low Loss and Magnetic Field-tuned Superconducting THz Metamaterial
Superconducting terahertz (THz) metamaterial (MM) made from superconducting
Nb film has been investigated using a continuous-wave THz spectroscopy with a
superconducting split-coil magnet. The obtained quality factors of the resonant
modes at 132 GHz and 450 GHz are about three times as large as those calculated
for a metal THz MM operating at 1 K, which indicates that superconducting THz
MM is a very nice candidate to achieve low loss performance. In addition, the
magnetic field-tuning on superconducting THz MM is also demonstrated, which
offer an alternative tuning method apart from the existed electric, optical and
thermal tuning on THz MM
A 400-GHz wideband high-gain quartz-based single-layered folded reflectarray antenna for terahertz applications
Antiferromagnetic magnonic charge current generation via ultrafast optical excitation
N\'eel spin-orbit torque allows a charge current pulse to efficiently
manipulate the N\'eel vector in antiferromagnets, which offers a unique
opportunity for ultrahigh density information storage with high speed. However,
the reciprocal process of N\'eel spin-orbit torque, the generation of ultrafast
charge current in antiferromagnets has not been demonstrated. Here, we report
the experimental observation of charge current generation in antiferromagnetic
metallic Mn2Au thin films using ultrafast optical excitation. The ultrafast
laser pulse excites antiferromagnetic magnons, resulting in instantaneous
non-equilibrium spin polarization at the antiferromagnetic spin sublattices
with broken spatial symmetry. Then the charge current is generated directly via
spin-orbit fields at the two sublattices, which is termed as the reciprocal
phenomenon of N\'eel spin-orbit torque, and the associated THz emission can be
detected at room temperature. Besides the fundamental significance on the
Onsager reciprocity, the observed magnonic charge current generation in
antiferromagnet would advance the development of antiferromagnetic THz emitter.Comment: 15 pages, 4 figures, this work was submitted to Nature Communications
on Jan. 4th, 2023, now is under the 3rd review proces
A liquid crystal-based multi-bit terahertz reconfigurable intelligent surface
Recently, the growing interest in reconfigurable intelligent surface (RIS) technology has spurred extensive research on its utilization in the terahertz (THz) regime. The reconfiguration of the THz field empowered by the RIS holds great significance for various practical RIS-aided implementations at THz frequencies. In this study, we present a multi-bit liquid crystal-based RIS that allows for the programmable control of THz waves. The proposed RIS is characterized by an achievable 3-bit working state as well as a near 270° maximum phase shift around 0.28 THz. This high degree of freedom in manipulating the phase of the reflected field provides flexibility in terahertz spatial beam reconfigurations. We show that the terahertz single-beam pattern can be steered continuously from 5° to 55° toward the desired angles while also allowing the adjustment of the beam number and beamwidth. Through this demonstration, we aim to contribute to the advancement of RIS technologies in the terahertz regime, paving the way for various RIS-aided applications such as THz wireless communications and beyond
A study of thermal effects in superconducting terahertz modulator by low temperature scanning laser microscope
We use low temperature scanning laser microscope (LTSLM) to study the Joule power distribution of superconducting (SC) terahertz (THz) modulator. The LTSLM scanning images record the SC state transformation process under different DC bias voltages. The change of THz transmission spectra can be well explained by the thermal effect in the devices observed by LTSLM. Hotspots are present in one THz modulator and the transmission spectra changes a lot after the hotspots show up. According to theoretical analysis, the appearance of hotspot may be helpful for improving the modulation speed. These results will be useful to understand the mechanism of SC THz modulator and design higher performance THz moduators
Magnetic flux instability in NbN films exposed to fast field sweep rates
Magneto-optical imaging of dendritic flux instability is reported for NbN films exposed to magnetic fields ramped at a fast rate (0.1–3.2 kT s−1 ). The results show that as the magnetic ramp rate increases, the temperature and field range of the instability extends significantly. In particular, the lower and upper threshold fields (Hth 1 and H , th 2 respectively) that bound the field range for dendritic instability are affected. The upper field is found to increase linearly with the applied field sweep rate, a behavior which is discussed in terms of a recent theoretical work (Vestgarden et al 2016 Phys. Rev. B 73 174511). The extended instability range should be taken into account in applications in which the superconducting films are exposed to rapid changes in the magnetic field
Polarization Effects on the Cellulose Dissolution in Ionic Liquids: Molecular Dynamics Simulations with Polarization Model and Integrated Tempering Enhanced Sampling Method
Conformation
of cellulose with various degree of polymerization
of <i>n</i> = 1–12 in ionic liquid 1,3-dimethylimidazolium
chloride ([C<sub>1</sub>mim]ÂCl) and the intermolecular interaction
between them was studied by means of molecular dynamics (MD) simulations
with fixed-charge and charge variable polarizable force fields, respectively.
The integrated tempering enhanced sampling method was also employed
in the simulations in order to improve the sampling efficiency. Cellulose
undergoes significant conformational changes from a gaseous right-hand
helical twist along the long axis to a flexible conformation in ionic
liquid. The intermolecular interactions between cellulose and ionic
liquid were studied by both infrared spectrum measurements and theoretical
simulations. Designated by their puckering parameters, the pyranose
rings of cellulose oligomers are mainly arranged in a chair conformation.
With the increase in the degree of polymerization of cellulose, the
boat and skew-boat conformations of cellulose appear in the MD simulations,
especially in the simulations with polarization model. The number
and population of hydrogen bonds between the cellulose and the chloride
anions show that chloride anion is prone to form HBs whenever it approaches
the hydroxyl groups of cellulose and, thus, each hydroxyl group is
fully hydrogen bonded to the chloride anion. MD simulations with polarization
model presented more abundant conformations than that with nonpolarization
model. The application of the enhanced sampling method further enlarged
the conformational spaces that could be visited by facilitating the
system escaping from the local minima. It was found that the electrostatics
interactions between the cellulose and ionic liquid contribute more
to the total interaction energies than the van der Waals interactions.
Although the interaction energy between the cellulose and anion is
about 2.9 times that between the cellulose and cation, the role of
cation is non-negligible. In contrast, the interaction energy between
the cellulose and water is too weak to dissolve cellulose in water