Photo sensing and energy harvesting based on exotic properties of quantum materials and new operation principles have great potentials to break the fundamental performance limit of conventional ...photodetectors and solar cells. As topological nontrivial materials, Weyl semimetals have demonstrated novel optoelectronic properties that promise potential applications in photo detection and energy harvesting arising from their gapless linear dispersion near Weyl nodes and Berry field enhanced nonlinear optical effect at the vicinity of Weyl nodes. In this work, we demonstrate robust photocurrent generation from charge separation of photoexctied electron-hole pairs at the edge of Td-WTe2, a type-II Weyl semimetal, due to crystalline-symmetry breaking along certain crystal fracture directions and possibly enhanced by robust fermi-arc type surface states. Using scanning photocurrent microscopy (SPCM) measurements, we further demonstrate that the edge current response is robust over a wide excitation photon energy. We find that this robust feature is highly generic, and shall arise universally in a wide class of quantum materials with similar crystal symmetries. In addition, possible connections between these edge photocurrents and topological properties of Weyl semimetals are explored. The robust and generic edge current response demonstrated in this work provides a new type of charge separation mechanism for photosensing and energy harvesting over broad wavelength range.
Article first introduces the VMCK (very minimum chirp keying) modulation. Based on this modulation, a QVMCK (quadrate VMCK) modulation utilized in UNB communication system is presented. In this ...scheme, input data is modulated onto both the initial phases of chirp signal and slope of instantaneous frequency. The power spectrum density of the VMCK and QVMCK modulated signals are analyzed. The BER performance of QVMCK schemes are simulated with only AWGN, which shows that the BER of QVMCK is less than 10 -5 when Eb/n0 is 13 dB.
The very minimum chirp keying (VMCK) is a novel ultra-narrow band communication scheme in which up-chirp or down-chirp waveform corresponding with data one or data zero. A new bit error rate (BER) ...formula in software radio (SFR) based demodulation system is put forward. Compared with the ordinary BER formula, the new formula is focused on the single period demodulation and taken filter effects into consideration.
We present simultaneous observations of three recurring jets in EUV and soft X-ray (SXR), which occurred in an active region on 2007 June 5. By comparing their morphological and kinematic ...characteristics in these two different wavelengths, we found that EUV and SXR jets had similar locations, directions, sizes and velocities. We also analyzed their spectral properties by using six spectral lines from the EUV Imaging Spectrometer (EIS) on board Hinode, and found that these jets had temperatures from 0.05 to 2.0 MK and maximum electron densities from 6.6\(\times10^{9}\) to 3.4\(\times10^{10}\) cm\(^{-3}\). For each jet, an elongated blue-shifted component and a red-shifted component at the jet base were simultaneously observed in Fe{\sc xii} \(\lambda\)195 and He{\sc ii} \(\lambda\)256 lines. The three jets had maximum Doppler velocities from 25 to 121 km s\(^{-1}\) in Fe{\sc xii} \(\lambda\)195 line and from 115 to 232 km s \(^{-1}\) in He{\sc ii} \(\lambda\)256 line. They had maximum non-thermal velocities from 98 to 181 km s\(^{-1}\) in Fe{\sc xii} \(\lambda\)195 line and from 196 to 399 km s\(^{-1}\) in He{\sc ii} \(\lambda\)256 line. We also examined the relationship between averaged Doppler velocities and maximum ionization temperatures of these three jets, and found that averaged Doppler velocities decreased with the increase of maximum ionization temperatures. In the photosphere, magnetic flux emergences and cancellations continuously took place at the jet base. These observational results were consistent with the magnetic reconnection jet model that magnetic reconnection between emerging magnetic flux and ambient magnetic field occurred in the lower atmosphere.
The very minimum chirp keying (VMCK) is proposed as a novel ultra-narrow band communication scheme employing one cycle up-chirp or down-chirp waveform in one bit. Based on the uniform method proposed ...in this paper, the non-DC offset VMCK waveforms have been worked out. Because of well-proportioned distribution of spectrum, this type of VMCK possesses less bandwidth and higher bandwidth efficiency. By comparing spectrum with sine-like wave very- minimum waveform difference keying (VWDK) and square wave very minimum shift keying (VMSK) in case of orthogonality, the VMCK UNB characteristics has been verified. The simulation result shows VMCK bandwidth efficiency can reach 10 bit/s/Hz with SNR of 2.7 × 103, which is practicable to implement for industrial use.
Division of focal plane (DoFP) polarimeters are composed of interlaced linear polarizers overlaid upon a focal plane array sensor. The interpolation is essential to reconstruct polarization ...information. However, current interpolation methods are based on the unrealistic assumption of noise-free images. Thus, it is advantageous to carry out denoising before interpolation. In this paper, we propose a principle component analysis (PCA) based denoising method, which works directly on DoFP images. Both simulated and real DoFP images are used to evaluate the denoising performance. Experimental results show that the proposed method can effectively suppress noise while preserving edges. (C) 2017 Optical Society of America
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