Band System Research Articles

Correlated flat bands and quantum spin liquid state in a cluster Mott insulator

Flat bands are rare in pristine solids and are unstable against electronic correlations or other types of long-range order. Unlike atomic-scale Hubbard systems or Moiré materials, where electronic correlations are either localized or long-ranged, pristine flat band systems with short-range interactions that do not break symmetry spontaneously are less known and intriguing. These systems could bridge the gap between atomic Mott insulators and Moiré correlated insulators, offering a unique platform to explore their mysterious relation. Using an analytical analysis, further verified by numerical calculations, we show that monolayer Nb3Cl8 is a unique flat band system with short-range interactions. We present clear evidence that it is a cluster Mott insulator, which nicely explains the electronic structure observed in angle-resolved photoemission spectroscopy. We further propose that monolayer Nb3Cl8 may constitute a rare example of molecular quantum spin liquid with flat bands.

Spatial Spectral Characteristics of Partial Discharge with Different Electrode Models

In this paper, the spatial spectral characteristics of partial discharge (PD) under different electrode models are mainly studied. In the initial corona discharge stage, the emission spectrum is mainly emitted by the N2(C3IIu→B3IIg) energy level transition of the N2 second positive band system. The spectrum is in the ultraviolet range of 294–436 nm, and its main peak is at 337 nm. The streamer discharge stage spectrum is mainly emitted by the energy level transition of the second positive band system of N2, N+, NO, and O+ and the first positive band system of N2(B3IIg→A3Σu+). In the gap of different polarity electrodes, the ultraviolet spectrum content near the positive polarity is more abundant. The UV spectra ranges are 202–225 nm and 229–292 nm, respectively. The discharge of the needle–sphere system is more intense in visible light and near-infrared light, with peaks at 500 nm and 777 nm, respectively. In addition, the PD process based on the finite element method is simulated by COMSOL Multiphysics software. The simulation results show that the distribution of high-energy electron density varies with the electrode spacing and discharge model. The influence of particle energy level transition on the spatial spectral characteristics of PD is verified. This work provides important insights and possibilities for future fluorescent fiberoptic sensing and positioning for spatial PD detection and positioning using spectral characteristic peaks as detection quantities or excitations.

8.0-pJ/bit BPSK Transmitter With LO Phase Steering and 52-Gbps Data Rate Operating at 246 GHz

This work investigates a broadband binary phase shift keying (BPSK) transmitter system with a measured data rate of 52 Gb/s and 8.0-pJ/bit transmitter efficiency. The transmitter features local oscillator (LO) multiplication, 360 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> LO phase steering for phased array applications, a power-efficient BPSK modulator, and a very compact power amplifier (PA) connected to a differential bond wire interface. By employing a low-order modulation scheme, the baseband (BB) chain can be implemented at a very low complexity, which benefits power consumption. Proving the concept, an integrated circuit (IC) is fabricated in a 130-nm silicon–germanium (SiGe) bipolar complementary metal–oxide–semiconductor (BiCMOS) technology with a ft/fmax of 350/450 GHz, covering 1.158 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . At 52 Gb/s, this circuit shows the highest reported data rate using BPSK modulation. The saturated output power of 3.5 dBm, while consuming 414 mW of direct-current (dc) power, results in a radio-frequency (RF) efficiency of 0.54%, which is a 28% improvement versus the state of the art. The high achieved data rate combined with circuit modules optimized for low power consumption results in a measured transmitter efficiency of 8.0 pJ/bit, improving the state of the art of complete transmitter systems in the same frequency band by 68% and 46% compared to BPSK and quadrature phase shift keying (QPSK) systems, respectively.

Theoretical study on low-lying states of silicon iodide:MRCI+Q calculation including spin-orbit coupling

High-level ab initio calculations are carried out to investigate the fine structure of electronic states correlating with the three lowest dissociation limits of the silicon iodide (SiI) molecule. The potential energy curves (PECs) of 23 Ʌ-S states and 45 Ω states are calculated by using multireference configuration interaction method with the Davidson correction (MRCI+Q). The spin-orbit coupling (SOC) effects are also accounted. Based on the calculated PECs, the spectroscopic constants of the bound states are evaluated, which are in a good agreement with previous experimental results. The predissociation mechanisms of the 22Δ state are studied, the perturbation on vibrational levels and predissociation channels are illuminated. Our investigation indicates that the higher vibrational levels (ν'≥ 7) of the doublet 12Σ+ are perturbed by the crossing quartet sate 14Σ−, which satisfactorily explains the perturbations of the (7,0) and (8,0) rovibronic band systems of the A-X transition detected in previous experiments. In addition, the transition dipole moments (TDMs), Franck-Condon factors (FCFs) and radiative lifetimes for spontaneous emission from the excited states to the ground state are evaluated.

Optical cable deployment versus fiber leasing: an operator’s perspective on CapEx savings for capacity upgrade in an elastic optical core network

Multiband (MB) and multifiber (MF) technologies get significant attention along with their individual pros and cons to solve the optical fiber capacity crunch problem. The MB system is more susceptible to nonlinear transmission impairments such as interchannel stimulated Raman scattering. On the contrary, MF solutions are costly due to the requirement of parallel fiber deployment. Therefore, it is necessary to find a hybrid solution using MB and MF technologies. This paper performs a techno-economic comparison between MF and MB technologies while taking a robust cost model. We propose, for the first time to our knowledge, a domain-knowledge-assisted, cost-effective network upgrade algorithm to enhance the overall network capacity while including minimum capital expenditure (CapEx). The proposed algorithm prioritizes the targeted deployment of cost-effective upgrade solutions in different links of the network to minimize the overall cost of the upgrade. The comparison between optical cable deployment and fiber leasing is captured to upgrade the overall network capacity with minimum cost-per-bit. Reported results show that a single fiber C+L band system can provide approximately 66.67% gain in terms of traffic admissibility compared to MF C band systems in smaller networks such as BT-UK, while considering fiber leasing. If operator owned dark fibers are not available in any of the links, numerical results show that the MF C+L band system in the BT-UK network can still provide CapEx savings of approximately up to 40.5% compared to the MF C band systems while minimizing the cost-per-bit of the network by approximately 21.9% to achieve the targeted network capacity of 150 Tbps. The effect of longer link length on the network upgrade cost is also studied in this paper. Reported result shows that, for larger geography such as the pan-Europe network, the channel launch power needs to be tuned to achieve the benefit of the MF C+L band compared to the MF C band system.

The discharge characteristics of capacitively coupled nitrogen plasma driven by 6∼50 MHz by optical emission spectra

The discharge characteristics of capacitively coupled nitrogen plasma driven by four different exciting radio frequencies (RF) of 6 MHz, 15 MHz, 35 MHz and 50 MHz are investigated by optical emission spectra (OES). The RF power change from 20 to 70 W and pressure change from 20 to 90 mTorr. The vibrational temperature Tv and rotational temperature Tr of N2 second positive system (C3Пu−B3Пg) and N2+ in the first negative band system (B2∑u+—X2∑g+state) are studied by comparing the experimental emission spectra with the calculated results. When the pressure is fixed at 40 mTorr, the spectral line intensity increases with the increase of RF power, and the vibrational temperature and rotational temperature of N2 and N2+ both increase. The vibrational temperature and rotational temperature of N2 and N2+ are the highest at 6 MHz and are the lowest at 15 MHz. When the RF power is fixed at 30 W, the vibrational temperature of N2 and N2+ both decrease and the rotational temperature of N2 and N2+ both increase with the increase of pressure. The vibration and rotational temperatures of N2 and N2+ are also the highest at 6 MHz. The influence of the driving frequency on the N2+ is greater than the influence on the N2, which may also be caused by the different response of the nitrogen ions to the driving frequency.

Optimization of LPI-FDA-MIMO Radar and MIMO Communication for Spectrum Coexistence

This paper studies the spectral efficiency of a multiple-input multiple-output (MIMO) radar with frequency diverse array (FDA) and a MIMO communication system in the same frequency band. To suppress mutual interference for both systems, and enhance low probability of intercept (LPI) capability of radar system, we propose a joint design of the transmit waveform and receive filter of radar, and the code-book employed by the communication system to form its space-time code matrix. Our problem formulationis to maximize the signal-to-interference-plus-noise ratio (SINR) and simultaneously minimize the probability of target detection of the radar signal under the peak-to-average ratio and communication rate constraints. Since the design problem is non-convex, we first transform it into three sub-optimization problems. An iterative algorithm is then developed to solve these subproblems to obtain the solution of the original problem. Simulation results show that the devised approach can effectively reduce the mutual interference as well as increase the SINR and LPI for radar system.

Statistical Device Activity Detection for OFDM-Based Massive Grant-Free Access

Existing works on grant-free access, proposed to support massive machine-type communication (mMTC) for the Internet of things (IoT), mainly concentrate on narrow band systems under flat fading. In contrast, this paper investigates massive grant-free access in a wideband system under frequency-selective fading. First, we present an orthogonal frequency division multiplexing (OFDM)-based massive grant-free access scheme. Then, we propose two different but equivalent models for the received pilot signal. Specifically, one directly models the received signal for actual devices, whereas the other can be interpreted as a signal model for virtual devices. The two signal models are insightful and essential for designing various device activity detection and channel estimation methods for OFDM-based massive grant-free access. Next, we systematically investigate statistical device activity detection under frequency-selective Rayleigh fading based on the two signal models. In particular, in the case without prior knowledge of device activities, we model device activities as deterministic but unknown binary constants and propose three maximum likelihood (ML) estimation-based device activity detection methods with different detection accuracies and computation times. In the case with prior knowledge of device activities, we model device activities as realizations of Bernoulli random variables with a known joint distribution, which appropriately incorporates the prior knowledge, and propose three maximum a posterior probability (MAP) estimation-based device activity methods, which further enhance the accuracies of the corresponding ML estimation-based methods at the cost of increased computational complexities. The proposed methods can meet diverse practical needs for OFDM-based massive grant-free access.

Low-cost, open-hardware shadow band system for diffuse irradiance measurements

In this work, we present the design, implementation, and test of a low-cost, open-hardware shadow band system that enables a pyranometer to measure global and diffuse irradiance. This system was implemented in Lima, Peru, and experimentally tested by contrasting it with a commercial reference system consisting of two pyranometers, one blocked by a shadow ring. The developed shadow band system automatically opens and closes to measure the global and diffuse irradiance consecutively, respectively, without requiring regular, manual adjustments of the shadow ring position as in the reference system. Thus, it potentially saves costs on equipment to characterize de irradiance components. Initial measurements in Lima indicate 100% and at least 23% of diffuse irradiance under cloudy and clear sky conditions, respectively.

Chiral spin liquid state of strongly interacting bosons with a moat dispersion: A Monte Carlo simulation

We consider a system of strongly interacting bosons in two dimensions with moat band dispersion which supports an infinitely degenerate energy minimum along a closed contour in the Brillouin zone. The system has been theoretically predicted to stabilize a chiral spin liquid (CSL) ground state. In the thermodynamic limit and vanishing densities, n→0, chemical potential, μ, of the uniform CSL state was shown to scale with n as μ∼n2log2n. Here we perform a Monte Carlo simulation to find the parametric window for particle density, n≲k0282π, where k0 is the linear size of the moat (the radius for a circular moat), for which the scaling ∼n2log2n in the equation of state of the homogeneous CSL is preserved. We variationally show that the uniform CSL state is favorable in an interval beyond the obtained scale and present a schematic phase diagram for the system. Our results offer some density estimates for observing the low-density behavior of CSL in time-of-flight experiments with a recently Floquet-engineered moat band system of ultracold atoms in Bracamontes et al. (2022), and for the recent experiments on emergent excitonic topological order in imbalanced electron–hole bilayers.

Bloch oscillations in moiré flat band systems

Bloch oscillations of wave packets in moiré flat band systems are investigated. We find that the real space trajectories and group velocity of wave packet undergo Bloch oscillations in the moiré flat band. It is shown that the Bloch dynamics is affected significantly by the magnitude and orientation of an applied in-plane electric field. In the presence of both external perpendicular magnetic field and in-plane electric field, confinement and de-confinement of cyclotron orbits occur which strongly depend on the relative strength of the applied fields.

Performance Analysis and Power Tilt Mitigation of Ultra-Wideband WDM Transmission Systems

Ultra-wideband (UWB) wavelength division multiplexing (WDM) transmission, which utilizes low-loss spectral windows of single-mode fiber for data transmission, is a highly promising method for increasing the capacity of optical communication. In this paper, we investigate the performance of a UWB WDM transmission system that covers the widely used C+L band as well as the additional O-, E-, and S-bands. We establish the transmission system for UWB and discuss the effects of the channel, including Kerr nonlinearity and inter-channel interference from inter-channel stimulated Raman scattering (ISRS) between O-, E-, S-, C-, and L-bands. Moreover, we demonstrate an optimization scheme for compensating the spectral power tilt caused by SRS in the S+C+L band system, which utilizes the Raman amplifier and the partition particle swarm optimization (PPSO) algorithm. The results show that the power tilt value of the algorithm is reduced from 18 to 2.93 dB, and the iteration speed is improved by 10% compared with the normal particle swarm algorithm. The scheme provides an efficient way to improve the generalized mutual information (GMI) performance of UWB WDM systems.

The 2ν3/ν2/ν5/ν3 + ν6 band system of CH3Br revisited: Anharmonic and Coriolis interactions in a four-level system near 1400 cm−1

The infrared spectrum of gaseous methyl bromide (CH3Br) in natural abundance has been analyzed with high resolution, between 1150 and 1700 cm−1. In this spectral region, two fundamental bands, ν2 (A1) and ν5 (E), an overtone 2ν3 (A1) and a combination band ν3 + ν6 (E) occur. The novelty of the present study consists in considering, besides the strong Coriolis and α-interactions coupling the v2 = 1 and v5 = 1 levels, a large variety of anharmonic and rovibrational interactions involving also the v3 = 2 and v3 = v6 = 1 levels. For this latter level, the data set belonging to the ν3 + ν6 combination band has been extended with respect to previous work of Ouahman et al. [Spectrochim. Acta45A (1989) 175–179], to about thousand assigned transitions with -6≤K·ΔK≤+16. Thanks to the completeness of the theoretical model, the global standard deviation of the reproduction of the experimental wavenumbers in the ν2/ν5 system was greatly improved with respect to the previous high-resolution study of Kwabia Tchana et al. [J. Mol. Spectrosc.228 (2004) 441–452]. For this Coriolis-interacting band system, two different reduction schemes, according to the theory of Stříteská et al. [J. Mol. Spectrosc.256 (2009) 135–140], were applied and were proved to be equally successful.

Circular Probability Error Based Inertial Navigation System Assists Ultra-Wide Band and Satellite Navigation System Intersection Area Fusion Positioning Algorithm

Circular Probability Error Based Inertial Navigation System Assists Ultra-Wide Band and Satellite Navigation System Intersection Area Fusion Positioning Algorithm

Observation of the electronic band system 23Σg--a3Πu of C2 in the vacuum ultraviolet region.

A systematic spectroscopic study of the dicarbon molecule C2 has important applications in various research fields, such as astrochemistry and combustion. In the short vacuum ultraviolet (VUV) wavelength region, recent theoretical calculations have predicted many absorption band systems of C2, but only few of them have been verified experimentally yet. In this work, we employed a tunable VUV laser radiation source based on the two-photon resonance-enhanced four-wave mixing method and a time-of-flight mass spectrometer to investigate the absorption bands of C2 in the VUV range of 64 000-66 000cm-1. The electronic transition 23Σg-(v')-a3Πu(v″) of C2 has been observed and identified experimentally for the first time. The term value Te for the 23Σg- state is determined to be 66 389.9 ± 0.5cm-1 above the ground state X1Σg+, and the vibrational and rotational constants are also determined. The experimentally measured spectroscopic parameters in this study are in excellent agreement with the theoretical results based on high-level abinitio calculations.

Line positions and intensities of the ν1 band of 12CH3I using mid-infrared optical frequency comb Fourier transform spectroscopy

We present a new spectral analysis of the ν1 and ν3+ν1−ν3 bands of 12CH3I around 2971 cm−1 based on a high-resolution spectrum spanning from 2800 cm–1 to 3160 cm–1, measured using an optical frequency comb Fourier transform spectrometer. From this spectrum, we previously assigned the ν4 and ν3+ν4−ν3 bands around 3060 cm–1 using PGOPHER, and the line list was incorporated in the HITRAN database. Here, we treat the two fundamental bands, ν1 and ν4, together with the perturbing states, 2ν2+ν3 and ν2+2ν6±2, as a four-level system connected via Coriolis and Fermi interactions. A similar four-level system is assumed to connect the two ν3+ν1−ν3 and ν3+ν4−ν3 hot bands, which appear due to the population of the low-lying ν3 state at room temperature, with the 2ν2+2ν3 and ν2+ν3+2ν6±2 perturbing states. This spectroscopic treatment provides a good global agreement of the simulated spectra with experiment, and hence accurate line lists and band parameters of the four connected vibrational states in each system. It also allows revisiting the analysis of the ν4 and ν3+ν4−ν3 bands, which were previously treated as separate bands, not connected to their ν1 and ν3+ν1−ν3 counterparts. Overall, we assign 4665 transitions in the fundamental band system, with an average error of 0.00071 cm–1, a factor of two better than earlier work on the ν1 band using conventional Fourier transform infrared spectroscopy. The ν1 band shows hyperfine splitting, resolvable for transitions with J ≤ 2 × K. Finally, the spectral intensities of 65 lines of the ν1 band and 7 lines of the ν3+ν1−ν3 band are reported for the first time using the Voigt line shape as a model in multispectral fitting. The reported line lists and intensities will serve as a reference for high-resolution molecular spectroscopic databases, and as a basis for line selection in future monitoring applications of CH3I.

Reconfigurable broadband metasurface with switchable functionalities in the visible range

In this article, we propose a broadband reconfigurable multifunctional meta-structure for the first time in the visible range. This device can be reconfigured between an achromatic metalens and a broadband absorber by switching the state of the phase change material (VO2). Our designed VO2 based novel multistage meta-atoms helped us overcome the inherent limitation of small optical contrast between PCM states in the visible regime, which hinders the realization of reconfigurable multifunctional devices in this band. We have used the finite-difference time-domain (FDTD) technique to characterize the designed multifunctional device. The structure showed a maximum switching ratio of 21.1dB between the on and off states in the operating band of 678nm to 795nm, the highest among previously reported broadband metalens-absorber systems in any design band. A small focal length shift within ±5% in the on state within this spectral band verifies the achromatic focusing characteristics of our reconfigurable meta-device. Our device proves the feasibility of reconfigurable metasurfaces with switchable functionalities in the visible band and has the prospects to bring about a revolution in next-generation integrated photonic platforms.

Jet-Cooled Phosphorescence Excitation Spectrum of the T1(n,π*)←S0 Transition of 4H-Pyran-4-one.

The 4H-pyran-4-one (4PN) molecule is a cyclic conjugated enone with spectroscopically accessible singlet and triplet (n,π*)excited states. Vibronic spectra of 4PN provide a stringent test of electronic-structure calculations, through comparison of predicted vs measured vibrational frequencies in the excited state. We report here the T1(n,π*) ← S0 phosphorescence excitation spectrum of 4PN, recorded under the cooling conditions of a supersonic free-jet expansion. The jet cooling has eliminated congestion appearing in previous room-temperature measurements of the T1 ← S0 band system and has enabled us to determine precise fundamental frequencies for seven vibrational modes of the molecule in its T1(n,π*) state. We have also analyzed the rotational contour of the 000 band, obtaining experimental values for spin-spin and spin-rotation constants of the T1(n,π*) state. We used the experimental results to test predictions from two commonly used computational methods, equation-of-motion excitation energies with dynamical correlation incorporated at the level of coupled cluster singles doubles (EOM-EE-CCSD) and time-dependent density functional theory (TDDFT). We find that each method predicts harmonic frequencies within a few percent of observed fundamentals, for in-plane vibrational modes. However, for out-of-plane modes, each method has specific liabilities that result in frequency errors on the order of 20-30%. The calculations have helped to identify a perturbation from the T2(π,π*) state that leads to unexpected features observed in the T1(n,π*) ← S0 origin band rotational contour.

Comparison Between Two Types Of Matrix Systems For Contact Tightness In Class-Ii Composite Restorations.

The reconstruction of proximal defects with tight contacts has always been a challenge for dental clinicians, especially with composite material. Recent literature shows that the most frequently used matrix systems for the restoration of proximal cavities are circumferential or sectional matrix band systems. The objective of this study was to compare the contact tightness that is achieved with these two matrix band systems when using composite material. A total of 30 patients, i.e., 60 cavities were selected in this quasi-experimental study. Patients with two cavities in the posterior teeth were selected. Both the cavities were restored with the circumferential system, i.e., Tofflemire and sectional matrix band system, i.e., Palodent plus on the same appointment. Hence both systems were used in every patient and then contact tightness assess was ed based on an evaluation criterion, i.e., Fédération Dentaire Internationale clinical criteria for evaluation of contact in direct and indirect restorations. To make a comparison between the two systems Chi square test was used and p<0.05. The mean age of the patients in the study was 31 years (SD, 7.59 years) with a range from 18 to 45 years. Most of the contact tightness in the Palodent matrix system was score 1 (n=33, 55%) and score 2 (n=17, 28.3%) while in Tofflemire was score 4 (n=28, 46.7%) and score 5 (n=19, 31.7%). Statistical analysis showed significance (p=.037) between Palodent matrix system contact tightness and Tofflemire. The sectional matrix band system was statistically superior to the circumferential matrix band system in achieving a tighter contact for class II composite restorations.

English

In previous works, we studied and analized the Darboux factorization for semi-infinite Hessenberg banded matrices. In this note, we prove that this kind of factorization can be used also for finite matrices. In addition, a new method for solving banded linear systems is provided. Finally, some numerical experiments are reported to show the effectiveness of the proposed method.