Wave Symmetry Research Articles

Hubbard Subbands and Superconductivity in the Infinite-Layer Nickelate

An effective two-dimensional two-band model for infinite-layer nickelates consists of bands obtained from $d_{x^2-y^2}$ and $s$--like orbitals. We investigate whether it could be mapped onto a single-band Hubbard model and the filling of Hubbard bands. We find that both one-band physics and a Kondo-lattice regime emerge from the same two-orbital model, depending on the strength of electronic correlations and the filling of the itinerant $s$-band. Next we investigate one-particle excitations by changing the screening. First, for weak screening the strong correlations push electrons out of the $s$-band so that the undoped nickelate is similar to a cuprate. Second, for strong screening the $s$ and $d_{x^2-y^2}$ bands are both partly filled and weakly couple. Particularly in this latter regime mapping to a one-band model gives significant spectral weight transfer between the Hubbard subbands. Finally we point out that the superconducting phases may have either $d$-wave or $s$-wave symmetry.

Nonlinear ultrasonic characterization of joint structures using backscatter guided waves

Abstract Joint structures made from plates or shells are frequently used in large constructions, such as oil storage tanks in petrochemical industries. The corrosion-induced metal loss often appears on the back side of the bottom plate supported by ground or sand. The welding residual stress and weight of shell walls accelerate the corrosion. Determining the severity of metal loss under the joint is challenging. This work uses the mode pair technique for nondestructive inspection of inaccessible regions in joint structures. A finite element analysis model simulates the transient responses of the incident and mode-converted fundamental and second harmonic plate waves. The second harmonic s0 plate wave satisfying the phase velocity matching condition accompanies the transmitted fundamental SH0 plate wave. A directional filter identifies every mode-converted plate wave by comparing the frequency spectra with the dispersion curves. Linear ultrasonic guided waves can detect inaccessible regions using mode-converted reflections. The symmetry of the linear mode-converted fundamental plate waves depends on the defect position and geometry, not the size. The mode-converted second harmonic guided wave can achieve better spatial resolution for defect sizing. The nonlinear parameter shows a proportional trend with an increasing thickness reduction. Experimental and numerical evidence reveals nonlinear ultrasonic guided wave technique has the potential for defect detection in joint structures.

New PWM inverter control based on optimal pulse pattern computation without phases symmetry constraints

The control of inverters has degrees of freedom that open the way to improve the output harmonic spectrum. Numerous works dealing with this objective have been proposed in the literature, particularly within the definition of switching angles. Among them, the well-known PWM techniques such as Quarter Wave Symmetry (QWS), Half Wave Symmetry (HWS), and Full Wave Symmetry (FWS) are based on Optimal Pulse Patterns (OPP) computation using symmetries angles constraints. In this paper to improve the harmonic quality, the symmetry angles constraints are not considered leading to a new OPP method: Phases Symmetry Relaxation (PSR). To highlight the interest in the proposed PSR method, an evaluation in terms of Weighted Total Harmonic Distortion (WTHD) is performed. Simulation and experimental tests are conducted in comparison with the well known FWS, highlighting the interest in the proposed PSR strategy.

Antiferromagnetic fluctuations and dominant dxy -wave pairing symmetry in nickelate-based superconductors

Motivated by recent experimental studies on superconductivity found in nickelate-based materials, we study the temperature dependence of the spin correlation and the superconducting pairing interaction within an effective two-band Hubbard model by the quantum Monte Carlo method. Based on parameters extracted from first-principles calculations, our intensive numerical results reveal that the pairing with a $d_{xy}$-wave symmetry firmly dominates over other pairings at low temperature, which is mainly determined by the Ni 3$d$ orbital. It is also found that the effective pairing interaction is enhanced as the on-site interaction increases, demonstrating that the superconductivity is driven by strong electron-electron correlation. Even though the $(\pi,\pi)$ antiferromagnetic correlation could be enhanced by electronic interaction, there is no evidence for long-range antiferromagnetic order exhibited in nickelate-based superconductors. Moreover, our results offer possible evidence that the pure electron correlation may not account for the charge density wave state observed in nickelates.

Symmetric waves are traveling waves of some shallow water scalar equations

Following a straightforward proof for symmetric solutions to be traveling waves by Pei (Exponential decay and symmetry of solitary waves to Degasperis‐Procesi equation. Journal of Differential Equations. 2020;269(10):7730‐7749), we prove that classical symmetric solutions of the highly nonlinear shallow water equation recently derived by Quirchmayr (A new highly nonlinear shallow water wave equation. Journal of Evolution Equations. 2016;16(3):539‐556) are indeed traveling waves, with further information on their steady structures. We also provide a simple proof that symmetric waves are traveling waves to the free surface evolution equation of moderate amplitude waves in shallow water.

Screening in a two-band model for superconducting infinite-layer nickelate

Starting from an effective two-dimensional two-band model for infinite layered nickelates, consisting of bands obtained from $d$ and $s$--like orbitals, we investigate to which extend it can be mapped onto a single-band Hubbard model. We identify screening of the more itinerant $s$-like band as an important driver. In absence of screening one strongly-correlated band gives an antiferromagnetic ground state. For weak screening, the strong correlations push electrons out of the $s$-band so that the undoped nickelate remains a Mott insulator with half filled $d$ orbitals. This regime markedly differs from the observations in high-$T_c$ cuprates and pairing with $s$-wave symmetry would rather be expected in the superconducting state. In contrast, for strong screening, the $s$ and $d_{x^2-y^2}$ bands are both partly filled and couple only weakly, so that one approximately finds a self-doped $d$ band as well as tendencies towards $d$-wave pairing. Particularly in the regime of strong screening mapping to a one-band model gives interesting spectral weight transfers when a second $s$ band is also partly filled. We thus find that both one-band physics and a Kondo-lattice--like regime emerge from the same two-orbital model, depending on the strength of electronic correlations and the size of the $s$-band pocket.

Optimal PWM in Three-Level Inverter for THD Minimization with Quarter Wave Symmetry Relaxed

Background: Previous works on total harmonic distortion (THD) minimization for multilevel inverters (MLI’s) has made a symmetrical approach that imposes Quarter Wave Symmetry (QWS) and Half Wave Symmetry (HWS) with the aim to restrict the computational difficulties to solve the finalized non-linear expressions. Objective: However, QWS constraint can be abolished, which leads to more generalized formulations and multiple solutions corresponding to minimum THD for complete modulation index-range. Methods: A systematic search approach using MATLAB in-build function is adopted to investigate ideal angles of switching related to three-level, three-phase inverter restricted to only HWS as a constraint for two and three (i.e., N= 2 and 3) switching transitions per quarter cycle. Results: On account of the effective minimization of the dominant low-order odd line voltage harmonics, the proposed pulse-width-modulation (PWM) scheme proved its superiority based on minimum THD% performance compared to the previously reported PWM techniques with both HWS and QWS being retained. Conclusion: The simulation, as well as experimental results to confirm the efficacy of the proposed non-symmetrical PWM scheme over the traditional PWM method restricted to QWS and HWS symmetries over the entire modulation-index range with added advantage of general formulation and multiple solutions.

Reversed spin of a ratchet motor on a vibrating water bed

A ratchet gear on a vibrating water bed exhibits a one-way spin. However, the spinning direction is opposite to that of the gear placed on the granular bed. The one-way spin is caused by the surface waves of water. Surface deformation causes transportation of the water element to rotate the gear. The spatial symmetry of the surface wave and gear geometry regulates the rotational torque. In this study, the same ratchet shows reversed motion between the granular and water beds, and the direction is not determined only by the ratchet geometry. The self-organization of the fluid medium caused by small agitation induces a nontrivial inversion of the spinning direction.

Doping-driven antiferromagnetic insulator-superconductor transition: A quantum Monte Carlo study

How superconductivity emerges in the vicinity of an antiferromagnetic insulating state is a long-standing issue of strong correlation physics. We study the transition from an antiferromagnetic insulator to a superconductor by hole-doping based on a bilayer generalization of a Hubbard-like model. The projector quantum Monte-Carlo simulations are employed, which are sign-problem-free both at and away from half-filling. An anisotropic Ising antiferromagnetic Mott insulating phase occurs at half-filling, which is weakened by hole-doping. Below a critical doping value, antiferromagnetism coexists with the singlet superconductivity, which is a pairing across each rung with an extended $s$-wave symmetry. As further increasing doping, the antiferromagnetic order vanishes, leaving only a superconducting phase. These results provide important information on how superconductivity appears upon doping the parent Mott-insulating state.

Observable effect of quantized cylindrical gravitational waves

We investigate the response of a model gravitational wave detector consisting of two particles to the quantized cylindrical gravitational waves and obtain a relation between the standard deviation of the distance between two particles and the distance from the source to the detector. It is found that the quantum effect carried by the cylindrical gravitational wave can be observed above Planck scale even though the source is as far as the cosmological horizon. The equation of motion for the change of the distance between two particles is obtained when the cylindrical gravitational waves pass. It is surprising that the dissipative term does not exist up to the first order approximation due to cylindrical symmetry of the gravitational wave.

Search for the Birefringence of Gravitational Waves with the Third Observing Run of Advanced LIGO-Virgo

Gravitational waves would attain birefringence during their propagation from distant sources to the Earth, when the charge, parity, and time reversal (CPT) symmetry is broken. If it was sizeable enough, such birefringence could be measured by the Advanced LIGO, Virgo, and KAGRA detector network. In this work, we place constraints on the birefringence of gravitational waves with the third observing run of this network, i.e., two catalogs GWTC-2 and GWTC-3. For the dispersion relation ω 2 = k 2 ± 2ζ k 3, our analysis shows the up-to-date strictest limit on the CPT-violating parameter, i.e., , at 68% confidence level. This limit is stricter by ∼5 times when compared to the existing one (∼2× 10−16 m) and stands for the first ∼10 GeV-scale test of the CPT symmetry in gravitational waves. The results of the Bayes factor strongly disfavor the birefringence scenario of gravitational waves.

Microscopic evidence for anisotropic multigap superconductivity in the CsV3Sb5 kagome superconductor

The recently discovered kagome superconductor CsV3Sb5 (Tc ≃ 2.5 K) has been found to host charge order as well as a non-trivial band topology, encompassing multiple Dirac points and probable surface states. Such a complex and phenomenologically rich system is, therefore, an ideal playground for observing unusual electronic phases. Here, we report anisotropic superconducting properties of CsV3Sb5 by means of transverse-field muon spin rotation (μSR) experiments. The fits of temperature dependences of in-plane and out-of-plane components of the magnetic penetration depth suggest that the superconducting order parameter may have a two-gap (s + s)-wave symmetry. The multiband nature of superconductivity could be further supported by the different temperature dependences of the anisotropic magnetic penetration depth γλ(T) and upper critical field {gamma }_{{{{{rm{B}}}}}_{{{{rm{c}}}}2}}(T). The relaxation rates obtained from zero field μSR experiments do not show noticeable change across the superconducting transition, indicating that superconductivity does not break time reversal symmetry.

Modification of monolayer 1T-VSe2 by selective deposition of vanadium and tellurium

Hetero-structures of transition metal dichalcogenide (TMD) layers offer vast possibilities of new materials properties. The growth behaviors of such TMD hetero-structures can be complex. In this study, we report the structure modification of a VSe2 monolayer by the molecular beam deposition of Te, V, or both. With a typical growth temperature of 300 °C and a nominal flux rate, we found that Te deposition leaves the VSe2 intact. Vanadium deposition, in contrast, leads to small clusters ordered in stripes along well-defined directions. The charge density wave symmetry of monolayer VSe2 surprisingly changes in small regions enclosed by such vanadium stripes. With V and Te co-deposition, a dramatic change of the monolayer surface structure to a (2 × 1) ordered phase is observed. This study illustrates the unexpected complexities involved in preparing even a simple bilayer TMD hetero-structure, such as VTe2/VSe2.

Tailoring bound states in the continuum in symmetric photonic crystal slabs by coupling strengths.

In this work, we investigate polarization-insensitive dual bound states in the continuum (BICs) at Γ point in symmetric photonic crystal (PhC) slabs. Especially, BICs are tailored by tuning intra- and intercellular optical coupling strengths of PhC slabs. Based on four different approaches, we realize the transition from BIC to quasi-BIC resonances with various dispersion behaviors while maintaining the symmetry of slabs. Also, we show the two resonances are lowest-order even and odd eigenmodes that can match the symmetry of the incident plane wave, and their quality (Q) factors follow the inverse quadratic law except for cases with larger perturbations. Furthermore, multipolar decomposition reveals that even quasi-BICs are dominated by the toroidal dipole and magnetic quadrupole, while odd quasi-BICs are governed by the magnetic dipole and electric quadrupole. Interestingly, an anomalous increase of the Q factor is observed in one case, which is attributed to the mode transformation. Finally, anisotropic coupling adjustment is discussed, which enriches the degrees of freedom to manipulate BICs. This work introduces a novel perspective to tailor BICs at Γ point in PhC slabs and has potential planar photonic applications for nonlinear enhancement and sensing.

Stripes versus superconductivity in the doped Hubbard model on the honeycomb lattice

We study the ground state of the doped Hubbard model on the honeycomb lattice in the small doping and strongly interacting region. The nature of the ground state by doping holes into the anti-ferromagnetic Mott insulating states on the honeycomb lattice remains a long-standing unsolved issue, even though tremendous efforts have been spent to investigate this challenging problem. An accurate determination of the ground state in this system is crucial to understand the interplay between the topology of Fermi surface and strong correlation effect. In this work, we employ two complementary, state-of-the-art, many-body computational methods -- constrained path (CP) auxiliary-field quantum Monte Carlo (AFQMC) with self-consistent constraint and density matrix renormalization group (DMRG) methods. Systematic and detailed cross-validations are performed between these two methods for narrow systems where DMRG can produce reliable results. AFQMC are then utilized to study wider systems to investigate the thermodynamic limit properties. The ground state is found to be a half-filled stripe state in the small doping and strongly interacting region. The pairing correlation shows $d$-wave symmetry locally, but decays exponentially with the distance between two pairs.

Distorted superconducting nodal line on a single Fermi surface in the anisotropic organic superconductor λ−(BETS)2GaCl4

The superconducting (SC) gap structure appearing in systems with single Fermi surface (FS) is generally described by the single gap function with $s$- or $d$-wave symmetry. The organic superconductor $\ensuremath{\lambda}$-(BETS)${}_{2}{\mathrm{GaCl}}_{4}$ [BETS = (${\mathrm{CH}}_{2}{)}_{2}{\mathrm{S}}_{2}{\mathrm{Se}}_{2}{\mathrm{C}}_{6}{\mathrm{Se}}_{2}{\mathrm{S}}_{2}$(${\mathrm{CH}}_{2}{)}_{2}$] endeavors to examine a novel SC gap structure on the distorted single cylindrical FS. Here, we show an example of the formation of the distorted SC nodal line by using the positive muon spin rotation (${\ensuremath{\mu}}^{+}\mathrm{SR}$) spectroscopy on $\ensuremath{\lambda}$-(BETS)${}_{2}{\mathrm{GaCl}}_{4}$. Our analysis method of the ${\ensuremath{\mu}}^{+}\mathrm{SR}$ data reveals that the nodal line has a narrower width than that of the traditional $d$-wave by the steepness factor of 4.6(2.1), and a flat part with the maximum gap exists. We found that the amplitude of the SC gap is $2\mathrm{\ensuremath{\Delta}}/{k}_{\text{B}}{T}_{c}$ = 3.9(2) and the in-plane penetration depth is ${\ensuremath{\lambda}}_{\text{ac}}$(0) = 560(5) nm. Our present study gives insight into the relation of the FS distortion and the unusual Cooper pair formation mediated by the anisotropic spin fluctuations.

Unconventional Superconductivity in Systems with Annular Fermi Surfaces: Application to Rhombohedral Trilayer Graphene

We show that in a two-dimensional electron gas with an annular Fermi surface, long-range Coulomb interactions can lead to unconventional superconductivity by the Kohn-Luttinger mechanism. Superconductivity is strongly enhanced when the inner and outer Fermi surfaces are close to each other. The most prevalent state has chiral p-wave symmetry, but d-wave and extended s-wave pairing are also possible. We discuss these results in the context of rhombohedral trilayer graphene, where superconductivity was recently discovered in regimes where the normal state has an annular Fermi surface. Using realistic parameters, our mechanism can account for the order of magnitude of T_{c}, as well as its trends as a function of electron density and perpendicular displacement field. Moreover, it naturally explains some of the outstanding puzzles in this material, that include the weak temperature dependence of the resistivity above T_{c}, and the proximity of spin singlet superconductivity to the ferromagnetic phase.

Unconventional charge density wave and photoinduced lattice symmetry change in the kagome metal CsV3Sb5 probed by time-resolved spectroscopy

The spin-orbit entangled quantum states in 4d/5d compounds, e.g., the Jeff=1/2 and Jeff=3/2 states, have attracted great interests for their unique physical roles in unconventional superconductivity and topological states. Here, the key role of tetragonal distortion is clarified, which determines the ground states of 4d1/5d1 systems to be the Jeff=3/2 one (e.g. K2NbCl6) or S=1/2 one (e.g. Rb2NbCl6). By tuning the tetragonal distortion via epitaxial strain, the occupation weights of dxy/dyz/dxz orbitals can be subtly modulated, competing with the spin-orbit coupling. Consequently, quantum phase transitions between S=1/2 state and Jeff=3/2 state, as well as between different Jeff=3/2 states, can be achieved, resulting in significant changes of local magnetic moments. Our prediction points out a reliable route to engineer new functionality of Jeff states in these quantum materials.

Аналіз морфології зубця Т у фазовому просторі на одноканальній електрокардіограмі у дітей із цукровим діабетом 1-го типу

Актуальність. Кардіоваскулярні порушення, що виникають у дітей із цукровим діабетом 1-го типу (ЦД-1), стають основною причиною смертності дорослих пацієнтів і відіграють головну роль у розвитку раптової серцевої смерті. Мета. Вивчення додаткових маркерів дисфункції міокарда у дітей із ЦД-1 шляхом аналізу одноканальної електрокардіографії (ЕКГ) у фазовому просторі. Матеріали та методи. Основну групу становили 83 пацієнти віком 4–16 років із ЦД-1, контрольну групу — 95 школярів віком 12–16 років. За допомогою комплексу «Фазаграф®»(Україна) досліджувалися й автоматично обчислювались параметри ЕКГ першого стандартного відведення. Запис ЕКГ здійснювали у положенні сидячи в стані відносного спокою. Аналіз ЕКГ проводився у часовій і фазовій областях. Результати. У дітей із ЦД-1 на відміну від їх здорових однолітків формується типовий патерн традиційної ЕКГ з високим і широким зубцем Р, подовженим інтервалом QTc, сплощеним та вузьким зубцем Т. Збільшення показника середньоквадратичного відхилення симетрії зубця Т (СКВ βТ) виявлялось у 68,7 % відсотків дітей, хворих на ЦД-1, та лише у 30,5 % практично здорових школярів. Показник СКВ βТ вірогідно зростає зі збільшенням тривалості захворювання на ЦД-1 у дітей. Групу високого ризику з розвитку серцево-судинних ускладнень становлять діти з тривалістю ЦД 3–5 років. Субоптимальний контроль глікемії та контроль високого ризику значно посилюють нестабільність функціонування міокарда від кардіоциклу до кардіоциклу. Висновки. Збільшення показника СКВ βТ може використовуватися як маркер ураження серця у дітей із ЦД-1. Раннє та систематичне обстеження з подальшим аналізом ЕКГ у фазовому просторі та оптимальний контроль глікемії можуть знизити рівень хронічних ускладнень з боку серця у дітей, хворих на ЦД-1.

BCS d -wave behavior in the terahertz electrodynamic response of electron-doped cuprate superconductors

Although cuprate superconductors have been intensively studied for the past decades, there is no consensus regarding the microscopic origin of their superconductivity. In this work, we measure the low-energy electrodynamic response of slightly underdoped and overdoped La$_{2-x}$Ce$_x$CuO$_4$ thin films using time-domain terahertz (THz) spectroscopy to determine the temperature and field dependence of the superfluid spectral weight. We show that the temperature dependence obeys the relation \textit{n$_s$} $\propto$ $1-(T/T_c)^2$, typical for dirty limit BCS-like $d$-wave superconductors. Furthermore, the magnetic field dependence was found to follow a sublinear $\sqrt{B}$ form, which supports predictions based on a $d$-wave symmetry for the superconducting gap. These observations imply that the superconducting order in these electron-doped cuprates can be well described in terms of a disordered BCS $d$-wave formalism.