scholarly journals Optical signatures of multifold fermions in the chiral topological semimetal CoSi

2020 ◽  
Vol 117 (44) ◽  
pp. 27104-27110 ◽  
Author(s):  
Bing Xu ◽  
Zhenyao Fang ◽  
Miguel-Ángel Sánchez-Martínez ◽  
Jorn W. F. Venderbos ◽  
Zhuoliang Ni ◽  
...  
Keyword(s):  
Optical Conductivity ◽  
Chemical Potential ◽  
Tight Binding ◽  
Low Frequency ◽  
Optical Response ◽  
Flat Band ◽  
Fermi Velocity ◽  
Topological Semimetal ◽  
Different Types ◽  
Topological Semimetals

We report the optical conductivity in high-quality crystals of the chiral topological semimetal CoSi, which hosts exotic quasiparticles known as multifold fermions. We find that the optical response is separated into several distinct regions as a function of frequency, each dominated by different types of quasiparticles. The low-frequency intraband response is captured by a narrow Drude peak from a high-mobility electron pocket of double Weyl quasiparticles, and the temperature dependence of the spectral weight is consistent with its Fermi velocity. By subtracting the low-frequency sharp Drude and phonon peaks at low temperatures, we reveal two intermediate quasilinear interband contributions separated by a kink at 0.2 eV. Using Wannier tight-binding models based on first-principle calculations, we link the optical conductivity above and below 0.2 eV to interband transitions near the double Weyl fermion and a threefold fermion, respectively. We analyze and determine the chemical potential relative to the energy of the threefold fermion, revealing the importance of transitions between a linearly dispersing band and a flat band. More strikingly, below 0.1 eV our data are best explained if spin-orbit coupling is included, suggesting that at these energies, the optical response is governed by transitions between a previously unobserved fourfold spin-3/2 node and a Weyl node. Our comprehensive combined experimental and theoretical study provides a way to resolve different types of multifold fermions in CoSi at different energy. More broadly, our results provide the necessary basis to interpret the burgeoning set of optical and transport experiments in chiral topological semimetals.

Quasi-Barrierless Submolecular Motion in Mechanically Interlocked Carbon Nanotubes

2020 ◽  
Author(s):  
Julia Villalva ◽  
Belén Nieto-Ortega ◽  
Manuel Melle-Franco ◽  
Emilio Pérez
Keyword(s):  
Density Functional ◽  
Close Contact ◽  
Tight Binding ◽  
Energetic Cost ◽  
Molecular Fragments ◽  
Activation Barriers ◽  
Flat Surfaces ◽  
Different Types ◽  
Atomically Flat ◽  
Derivatives Of

The motion of molecular fragments in close contact with atomically flat surfaces is still not fully understood. Does a more favourable interaction imply a larger barrier towards motion even if there are no obvious minima? Here, we use mechanically interlocked rotaxane-type derivatives of SWNTs (MINTs) featuring four different types of macrocycles with significantly different affinities for the SWNT thread as models to study this problem. Using molecular dynamics, we find that there is no direct correlation between the interaction energy of the macrocycle with the SWNT and its ability to move along or around it. Density functional tight-binding calculations reveal small (<2.5 Kcal·mol-1) activation barriers, the height of which correlates with the commensurability of the aromatic moieties in the macrocycle with the SWNT. Our results show that macrocycles in MINTs rotate and translate freely around and along SWNTs at room temperature, with an energetic cost lower than the rotation around the C−C bond in ethane.<br>

scholarly journals Linear and nonlinear optical responses in the chiral multifold semimetal RhSi

2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Zhuoliang Ni ◽  
B. Xu ◽  
M.-Á. Sánchez-Martínez ◽  
Y. Zhang ◽  
K. Manna ◽  
...  
Keyword(s):  
Nonlinear Optical ◽  
Chemical Potential ◽  
Technological Development ◽  
Optical Responses ◽  
Chiral Magnetic Effect ◽  
Hole Band ◽  
Linear And Nonlinear ◽  
Characteristic Features ◽  
Topological Semimetals ◽  
Terahertz Emission Spectroscopy

AbstractChiral topological semimetals are materials that break both inversion and mirror symmetries. They host interesting phenomena such as the quantized circular photogalvanic effect (CPGE) and the chiral magnetic effect. In this work, we report a comprehensive theoretical and experimental analysis of the linear and nonlinear optical responses of the chiral topological semimetal RhSi, which is known to host multifold fermions. We show that the characteristic features of the optical conductivity, which display two distinct quasi-linear regimes above and below 0.4 eV, can be linked to excitations of different kinds of multifold fermions. The characteristic features of the CPGE, which displays a sign change at 0.4 eV and a large non-quantized response peak of around 160 μA/V2 at 0.7 eV, are explained by assuming that the chemical potential crosses a flat hole band at the Brillouin zone center. Our theory predicts that, in order to observe a quantized CPGE in RhSi, it is necessary to increase the chemical potential as well as the quasiparticle lifetime. More broadly, our methodology, especially the development of the broadband terahertz emission spectroscopy, could be widely applied to study photogalvanic effects in noncentrosymmetric materials and in topological insulators in a contact-less way and accelerate the technological development of efficient infrared detectors based on topological semimetals.

scholarly journals Smart optical cross dipole nanoantenna with multibeam pattern

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Seyyed Mohammad Mehdi Moshiri ◽  
Najmeh Nozhat
Keyword(s):  
Radiation Pattern ◽  
Chemical Potential ◽  
Monolayer Graphene ◽  
Absorption Characteristic ◽  
Radiation Beam ◽  
Directional Radiation ◽  
Chemical Potentials ◽  
Different Types ◽  
Absorption Power ◽  
Maximum Directivity

AbstractIn this paper, an optical smart multibeam cross dipole nano-antenna has been proposed by combining the absorption characteristic of graphene and applying different arrangements of directors. By introducing a cross dipole nano-antenna with two V-shaped coupled elements, the maximum directivity of 8.79 dBi has been obtained for unidirectional radiation pattern. Also, by applying various arrangements of circular sectors as director, different types of radiation pattern such as bi- and quad-directional have been attained with directivities of 8.63 and 8.42 dBi, respectively, at the wavelength of 1550 nm. The maximum absorption power of graphene can be tuned by choosing an appropriate chemical potential. Therefore, the radiation beam of the proposed multibeam cross dipole nano-antenna has been controlled dynamically by applying a monolayer graphene. By choosing a suitable chemical potential of graphene for each arm of the suggested cross dipole nano-antenna without the director, the unidirectional radiation pattern shifts ± 13° at the wavelength of 1550 nm. Also, for the multibeam nano-antenna with different arrangements of directors, the bi- and quad-directional radiation patterns have been smartly modified to uni- and bi-directional ones with the directivities of 10.1 and 9.54 dBi, respectively. It is because of the graphene performance as an absorptive or transparent element for different chemical potentials. This feature helps us to create a multipath wireless link with the capability to control the accessibility of each receiver.

Enhanced magneto-optical response due to the flat band in nanoribbons made from the α−T3 lattice

2019 ◽  
Vol 99 (4) ◽  
Author(s):  
Yan-Ru Chen ◽  
Yong Xu ◽  
Jun Wang ◽  
Jun-Feng Liu ◽  
Zhongshui Ma
Keyword(s):  
Optical Response ◽  
Flat Band

scholarly journals Theoretical treatment of tight-binding inhibition of an enzyme. Ribonuclease inhibitor as special case

1988 ◽  
Vol 253 (2) ◽  
pp. 517-522 ◽  
Author(s):  
J M Fominaya ◽  
J M García-Segura ◽  
M Ferreras ◽  
J G Gavilanes
Keyword(s):  
Tight Binding ◽  
Theoretical Treatment ◽  
Inhibitor Protein ◽  
Ribonuclease Inhibitor ◽  
Rat Testis ◽  
Binding Inhibition ◽  
Different Types ◽  
Functional Consequences ◽  
Inhibitor System ◽  
Special Case

A general treatment of very tight-binding inhibition is described. It was applied to purified endogenous RNAase inhibitor from rat testis. This treatment discriminates among the different types of inhibition and allows for calculation of the inhibition parameters. When very tight-binding inhibitions are studied at similar molar concentrations of both enzyme and inhibitor, a further approach is required. This is also described and applied to the RNAase inhibitor. A Ki value of 3.2 x 10(-12) M was found for this inhibitor protein. On the basis of this result, it was considered inappropriate to classify this type of inhibitor in terms of competitive or non-competitive, as has been done for such inhibitors so far. Functional consequences of this analysis are discussed for the RNAase-RNAase inhibitor system.

Ground Attenuation Factor Based on Measurements

2021 ◽  
Vol 263 (3) ◽  
pp. 3436-3447
Author(s):  
Dan Lin ◽  
Andrew Eng
Keyword(s):  
Near Field ◽  
Attenuation Factor ◽  
Measurement Data ◽  
Low Frequency ◽  
Sound Sources ◽  
Frequency Sound ◽  
Sound Levels ◽  
Different Types ◽  
Noise Measurements ◽  
Field Sound

Assumptions made on the ground types between sound sources and receivers can significantly impact the accuracy of environmental outdoor noise prediction. A guideline is provided in ISO 9613-2 and the value of ground factor ranges from 0 to 1, depending on the coverage of porous ground. For example, a ground absorption factor of 1 is suggested for grass ground covers. However, it is unclear if the suggested values are validated. The purpose of this study is to determine the sound absorption of different types of ground by measurements. Field noise measurements were made using an omnidirectional loudspeaker and two microphones on three different types of ground in a quiet neighborhood. One microphone was located 3ft from the loudspeaker to record near field sound levels in 1/3 and 1 octave bands every second. The other microphone was located a few hundred feet away to record far field sound in the same fashion as the near field microphone. The types of ground tested were concrete, grass, and grass with trees. Based on the measurement data, it was found that grass and trees absorb high frequency sound well and a ground factor of 1 may be used for 500Hz and up when using ISO 9613-2 methodology. However, at lower frequencies (125 Hz octave band and below), grassy ground reflects sound the same as concrete surfaces. Trees absorb more low frequency sound than grass, but less than ISO 9613-2 suggested.

Electronic Structure Transformation in a Magnetized Topological Semimetal

2021 ◽  
Vol 1 ◽  
Keyword(s):  
Electronic Structure ◽  
Domain Walls ◽  
Magnetic Domain ◽  
Localized States ◽  
Structure Transformation ◽  
Nodal Lines ◽  
Topological Semimetal ◽  
Magnetic Domain Walls ◽  
Magnetic Orders ◽  
Topological Semimetals

We theoretically show that the nodal structures in topological semimetals, including Weyl points and nodal lines, can be switched by magnetic orders, accompanied by localized states at magnetic domain walls.

Study of the significance of the ph of the substrate of the biogas installation during treating it with a low-frequency electromagnetic field

2021 ◽  
pp. 106-114
Author(s):  
M.M. Zablodsky ◽  
◽  
P.B. Klendiy ◽  
O. P. Dudar ◽  
◽  
...  
Keyword(s):  
Electromagnetic Field ◽  
Electromagnetic Induction ◽  
Ph Value ◽  
Low Frequency ◽  
Decisive Role ◽  
Methane Fermentation ◽  
Different Types ◽  
Substrate Ph ◽  
Fermentation Substrate ◽  
Industrial Frequency

The article considers the issue of studying the value of pH, substrate in the process of methane fermentation in the mesophilic regime and the influence of the electromagnetic field of industrial frequency. The aim is to investigate the influence of electromagnetic fields on the pH value of the substrate during fermentation. Different types of microorganisms are involved in the process of methanogenesis, and the decisive role in it is played by methane-forming archaea, which are most sensitive to pH and should be in the range of 6.5 - 8. Therefore, it is necessary to check the effect of low frequency electromagnetic field on substrate pH. The study was performed for 25 days on two substrates, one of which was exposed to a low-frequency electromagnetic field with an electromagnetic induction of 3.5 mT. The research results show that the pH value of the substrate exposed to the electromagnetic field during the methane fermentation process was within acceptable limits, and the second substrate decreased, that is, it was acidified. Key words: methane fermentation, substrate, pH value, electromagnetic field

scholarly journals Low Frequency Noise Remove from EEG Signal

2020 ◽  
Vol 9 (1) ◽  
pp. 1510-1513
Keyword(s):  
Human Brain ◽  
Random Noise ◽  
Low Frequency ◽  
Frequency Noise ◽  
Eeg Signal ◽  
Low Frequency Noise ◽  
Frequency Range ◽  
Average Value ◽  
Different Types ◽  
The Brain

The electrical activity of the brain recorded by EEG which used to detect different types of diseases and disorders of the human brain. There is contained a large amount of random noise present during EEG recording, such as artifacts and baseline changes. These noises affect the low -frequency range of the EEG signal. These artifacts hiding some valuable information during analyzing of the EEG signal. In this paper we used the FIR filter for removing low -frequency noise(<1Hz) from the EEG signal. The performance is measured by calculating the SNR and the RMSE. We obtained RMSE average value from the test is 0.08 and the SNR value at frequency(<1Hz) is 0.0190.

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