Double-peak Structure Research Articles

Strongly scattered phonon heat transport of the candidate Kitaev material Na2Co2TeO6

We studied the field dependent thermal conductivity ($\kappa$) of Na$_2$Co$_2$TeO$_6$, a compound considered as the manifestation of the Kitaev model based on the high-spin $d^7$ Co$^{2+}$ ions. We found that in-plane magnetic fields beyond a critical value $B_c \approx$~10 T are able to drastically enhance $\kappa$ at low temperatures, resulting in a double-peak structure of $\kappa(T)$ that closely resembles the behavior of $\alpha$-RuCl$_3$. This result suggests that heat transport in Na$_2$Co$_2$TeO$_6$ is primarily phononic, and it is strongly affected by scattering from magnetic excitations that are highly tunable by external fields. Interestingly, for magnetic fields $B // a$ (i.e., along the zigzag direction of the Co-Co bonds), there is an extended field range which separates the long-range magnetic order for $B\leq B_c\approx10$ T and the partially spin-polarized gapped high-field phase for $B\gtrsim 12$ T. The low-energy phonon scattering is particularly strong in this field range, consistent with the notion that the system becomes a quantum spin liquid with prominent spin fluctuations down to energies of no more than 2 meV.

Triply Differential Positron and Electron Impact Ionization of Argon: Systematic Features and Scaling

Triply differential data are presented for the 200 eV positron and electron impact ionization of argon. Six electron emission energies between 2.6 and 19 eV, and for scattering angles of 2, 3, and 4 degrees cover a momentum transfer range of 0.16 to 0.31 a.u. The binary and recoil intensities are fitted using a double peak structure in both regions, which, for the present kinematic conditions, are unresolved. The fitted peak intensities and angular positions are shown to have systematic dependences as a function of the momentum transfer and kinematic emission angle, respectively, and illustrate projectile charge effects. A comparison with available theories is made where it is seen that the most notable differences include the fact that for the binary lobe, the observed intensity for emission angles around 100° is absent in the theories, and the theoretical predications overestimate the importance of recoil interactions.

Feshbach resonances in D + HD(v=1, j=0) reaction at low collision energies.

Feshbach resonances in D + HD(v=1, j=0) reaction are studied by using the time-independent quantum method. The integral cross section (ICS) results present three Feshbach resonance peaks, which are different from H + HD(v=1, j=0) reaction dominated by only one peak. These resonances are attributed to coupling with adiabatic effective potentials of D + HD(v=1, j=1) reaction, and the most obvious peak is contributed by J= 1 at 83.16 cm-1 collision energy. For J=0 and 2, the resonances are related with the same L partial wave and present a double-peak structure in total ICS. The characteristics of product angular distribution show that the resonance of J=1 is long-lived, while the lifetimes are relatively shorter for the resonance of J= 0 and 2.

The self-focusing condition of a charged particle beam in a resistive plasma

The self-focusing condition of a charged particle beam in a resistive plasma has been studied. When plasma heating is weak, the beam focusing is intensified by increasing the beam density or velocity. However, when plasma heating is strong, the beam focusing is only determined by the beam velocity. Especially, in weak heating conditions, the beam trends to be focused into the centre as a whole, and in strong heating conditions, a double-peak structure with a hollow centre is predicted to appear. Furthermore, it is found that the beam radius has a significant effect on focusing distance: a larger the beam radius will result in a longer focusing distance. Simulation results also show that when the beam radius is large enough, filamentation of the beam appears. Our results will serve as a reference for relevant beam–plasma experiments and theoretical analyses, such as heavy ion fusion and ion-beam-driven high energy density physics.

Orientation dependence of high-order harmonic generation in graphene

We investigate the orientation dependence of high-order harmonic generation (HHG) in graphene by solving the semiconductor Bloch equations. The tight-binding approximation including up to the third-nearest-neighbor atoms is used to model the graphene. Our simulations show that the orientation dependence of HHG shows different patterns for different harmonics. With increasing the laser intensity, these patterns become similar except for a double-peak structure shown in lower-order harmonics. The double-peak structure appears at high laser intensity due to the contribution of the harmonic perpendicular to the laser polarization direction. The harmonic yield is decomposed as the contributions of the nearest-neighbor interaction, the second-nearest-neighbor interaction, and the third-nearest-neighbor interaction. Our results show that the harmonic yields are mainly contributed by the nearest-neighbor interaction, but the third-nearest-neighbor interaction also plays an important role and modifies the orientation dependence.

Clock model interpolation and symmetry breaking in O(2) models

Motivated by recent attempts to quantum simulate lattice models with continuous Abelian symmetries using discrete approximations, we define an extended-O(2) model by adding a $\gamma \cos(q\varphi)$ term to the ordinary O(2) model with angular values restricted to a $2\pi$ interval. In the $\gamma \rightarrow \infty$ limit, the model becomes an extended $q$-state clock model that reduces to the ordinary $q$-state clock model when $q$ is an integer and otherwise is a continuation of the clock model for noninteger $q$. By shifting the $2\pi$ integration interval, the number of angles selected can change discontinuously and two cases need to be considered. What we call case $1$ has one more angle than what we call case $2$. We investigate this class of clock models in two space-time dimensions using Monte Carlo and tensor renormalization group methods. Both the specific heat and the magnetic susceptibility show a double-peak structure for fractional $q$. In case $1$, the small-$\beta$ peak is associated with a crossover, and the large-$\beta$ peak is associated with an Ising critical point, while both peaks are crossovers in case $2$. When $q$ is close to an integer by an amount $\Delta q$ and the system is close to the small-$\beta$ Berezinskii-Kosterlitz-Thouless transition, the system has a magnetic susceptibility that scales as $\sim 1 / (\Delta q)^{1 - 1/\delta'}$ with $\delta'$ estimates consistent with the magnetic critical exponent $\delta = 15$. The crossover peak and the Ising critical point move to Berezinskii-Kosterlitz-Thouless transition points with the same power-law scaling. A phase diagram for this model in the $(\beta, q)$ plane is sketched. These results are possibly relevant for configurable Rydberg-atom arrays where the interpolations among phases with discrete symmetries can be achieved by varying continuously the distances among atoms and the detuning frequency.

Quasi-two-day wave modulation of carbon dioxide in the mesosphere and lower thermosphere

In this paper, we report the quasi-two-day wave (QTDW) in daytime only SABER CO2 in January 2003. The QTDW in CO2 of ∼7 ppmv or 3–4% shows double peak structures at mid and low latitudes of both hemispheres. We compare the SABER measured QTDW disturbance in CO2 and temperature to those in the eCMAM (the extended Canadian Middle Atmosphere Model). Good agreement of QTDW CO2 spatial and temporal variations is seen, especially at southern mid-latitudes. eCMAM outputs are further analyzed to show that the QTDW in CO2 mixing ratio is mainly driven by both vertical transport and meridional advection. Because waves in vertical transport can be derived by temperature disturbance via a so-called adiabatic displacement approach, we can estimate the QTDW in CO2 mixing ratio from the SABER QTDW in temperature assuming meridional advection is weak at low and mid-latitudes.

Photospheric Radius Expansion and a Double-peaked Type-I X-Ray Burst from GRS 1741.9–2853

Abstract We present an analysis of two type-I X-ray bursts observed by NuSTAR originating from the very faint transient neutron star (NS) low-mass X-ray binary GRS 1741.9–2853 during a period of outburst in 2020 May. We show that the persistent emission can be modeled as an absorbed, Comptonized blackbody in addition to Fe Kα emission, which can be attributed to relativistic disk reflection. We measure a persistent bolometric, unabsorbed luminosity of L bol = 7.03 − 0.05 + 0.04 × 10 36 erg s − 1 , assuming a distance of 7 kpc, corresponding to an Eddington ratio of 4.5%. This persistent luminosity combined with light-curve analysis leads us to infer that the bursts were the result of pure He burning rather than mixed H/He burning. Time-resolved spectroscopy reveals that the bolometric flux of the first burst exhibits a double-peaked structure, placing the source within a small population of accreting NSs that exhibit multiple-peaked type-I X-ray bursts. We find that the second, brighter burst shows evidence for photospheric radius expansion (PRE) and that at its peak, this PRE event had an unabsorbed bolometric flux of F peak = 2.94 − 0.26 + 0.28 × 10 − 8 erg cm − 2 s − 1 . This yields a new distance estimate of d = 9.0 ± 0.5 kpc, assuming that this corresponds to the Eddington limit for pure He burning on the surface of a canonical NS. Additionally, we performed a detailed timing analysis that failed to find evidence for quasi-periodic oscillations or burst oscillations, and we place an upper limit of 16% on the rms variability around 589 Hz, the frequency at which oscillations have previously been reported.

Inhomogeneous solutions to thermal Hartree–Fock equations in first-order phase transitions

It is shown that the damping algorithm for the density matrix in self-consistent-field iterations, originally proposed for quantum chemistry of molecules in the ground state, can yield convergent solutions to thermal Hartree–Fock equations representing inhomogeneous domain structures in first-order phase transitions. A lattice gas of spinless Fermions with nearest-neighbour attractive interaction is analysed as an illustration. In the metastable or unstable region of the phase diagram, numerical solutions converge to phase-separated states consisting of gas and liquid domains, characterised by a double-peak structure in the single-particle energy spectrum. Broadening of the energy spectrum due to quantum-mechanical tunnelling effect is also demonstrated. The present method would facilitate direct numerical access to phase-transition regions of various quantum/classical systems without causing breakdown.

Influence of water storage on deflagration characteristics of methane in confined space

Comparative experiments were conducted under different water level heights and methane concentration conditions using a self-designed explosion experiment pipeline. The results showed that, in comparison with the scenario without water storage, when the water level was 2 cm and methane concentration was 6.5–12.5%, there was a dual effect including a pressure decrease caused by the endothermic cooling of liquid water and a pressure increase caused by the expansion of water vapour. These effects caused the pressure time history curve to exhibit a double-peak or multi-peak structure, and the average decrease in the peak deflagration pressure was 23.76%. The heat of vaporisation absorbed by the stored water and barrier effect of water vapour on the transfer of the heat slowed down the increase in the deflagration temperature. The average decrease in the peak deflagration temperature of methane was 13.82%, and the time to reach the peak deflagration temperature was extended as a whole, with an average delay of 0.22 s. Water storage also changed the shape of the deflagration flame front, which exhibited ‘knife’, ‘V’, and ‘crescent’ structures. Moreover, the flame propagation speed was significantly reduced, with the peak and average flame propagation speeds decreased by 83.3% and 83.6%, respectively. The research results can provide a certain reference for preventing gas explosions in typical confined spaces, and also help to explore new anti-explosion methods, which can be applied to marine equipment such as ships.

Unusual excitations and double-peak specific heat in a bond-alternating spin-1 K−Γ chain

One-dimensional gapped phases that avoid any symmetry breaking have drawn enduring attention. In this paper, we study such phases in a bond-alternating spin-1 $K$-$\Gamma$ chain built of a Kitaev ($K$) interaction and an off-diagonal $\Gamma$ term. In the case of isotropic bond strength, a Haldane phase, which resembles the ground state of a spin-$1$ Heisenberg chain, is identified in a wide region. A gapped Kitaev phase situated at dominant ferromagnetic and antiferromagnetic Kitaev limits is also found. The Kitaev phase has extremely short-range spin correlations and is characterized by finite $\mathbb{Z}_2$-valued quantities on bonds. Its lowest entanglement spectrum is unique, in contrast to the Haldane phase whose entanglement spectrum is doubly degenerate. In addition, the Kitaev phase shows a double-peak structure in the specific heat at two different temperatures. In the pure Kitaev limit, the two peaks are representative of the development of short-range spin correlation at $T_h \simeq 0.5680$ and the freezing of $\mathbb{Z}_2$ quantities at $T_l \simeq 0.0562$, respectively. By considering bond anisotropy, regions of Haldane phase and Kitaev phase are enlarged, accompanied by the emergence of dimerized phases and three distinct magnetically ordered states.

The Climatology and the Midwinter Suppression of the Cold Season North Pacific Storm Track in CMIP6 Models

AbstractThe reproducibility of climatology and the midwinter suppression of cold season North Pacific storm track (NPST) in historical runs of 18 CMIP6 models is evaluated against the NCEP reanalysis data. The results show that the position of the climatological peak area of 850 hPa meridional eddy heat flux (v′t′850) is well captured by these models. The spatial patterns of climatological v′t′850 are basically consistent with the NCEP reanalysis. Generally, NorESM2-LM and CESM2-WACCM present a relatively strong capability to reproduce the climatological amplitude of v′t′850 with lower RMSE than the other models. Compared with CMIP5 models, the inter-model spread of v′t′850 climatology among the CMIP6 models is smaller, and their multi-model ensemble is closer to the NCEP reanalysis. The geographical distribution in more than half of the selected models is further south and east. For the subseasonal variability of v′t′850, nearly half of the models exhibit a double-peak structure. In contrast, the apparent midwinter suppression in the NPST represented by the 250 hPa filtered meridional wind variance (v′v′250) is reproduced by all the selected models.In addition, the present study investigates the possible reasons for simulation biases regarding climatological NPST amplitude. It is found that a higher model horizontal resolution significantly intensifies the climatological v′v′250. There is a significant in-phase relationship between climatological v′t′250 and the intensity of the East Asian winter monsoon (EAWM). However, the climatological v′t′850 is not sensitive to the model grid spacing. Additionally, the climatological low-tropospheric atmospheric baroclinicity is uncorrelated with climatological v′v′250. The stronger climatological baroclinic energy conversion is associated with the stronger climatological v′t′850.

Evolution of magnetic dipole strength in Sn100−140 isotope chain and the quenching of nucleon g factors

The evolution of electromagnetic transitions along isotope chains is of particular importance for the nuclear structure and dynamics, as well as for the r-process nucleosynthesis. Recent measurement of inelastic proton scattering on even-even $^{112-124}$Sn isotopes provides a novel insight into the isotopic dependence of E1 and M1 strength distributions. We investigate M1 transitions in even-even $^{100-140}$Sn isotopes from a theoretical perspective, based on relativistic nuclear energy density functional. The M1 transition strength distribution is characterized by an interplay between single and double-peak structures, that can be understood from the evolution of single-particle states, their occupations governed by the pairing correlations, and two-quasiparticle transitions involved. It is shown that discrepancy between model calculations and experiment on B(M1) transition strength is considerably reduced than previously known, and the quenching of the g-factors for the free nucleons needed to reproduce the experimental data on M1 transition strength amounts $g_{eff}/g_{free}$=0.80-0.93. Since some of the B(M1) strength above the neutron threshold may be missing in the inelastic proton scattering measurement, further experimental studies are required to confirm if only small modifications of the bare g-factors are actually needed when applied in finite nuclei.

An entropic simulational study of the spin-1 Baxter–Wu model in a crystal field

We investigate the critical behavior of the two-dimensional spin-1 Baxter–Wu model in a crystal field using entropic sampling simulations, based on the Wang–Landau method, with the joint density of states. We obtain the temperature–crystal field phase diagram, which includes a tetracritical line ending at a pentacritical point. A finite-size scaling analysis of the maximum of the specific heat, while changing the crystal field anisotropy, is used to obtain a precise location of the pentacritical point. Our results give the critical temperature and crystal field as Tpc=0.98030(10) and Dpc=1.68288(62). We also detect that at the first-order region of the phase diagram, the specific heat exhibits a double peak structure as in the Schottky-like anomaly, which is associated with an order–disorder transition.

Effects of divertor electrical drifts on particle distribution and detachment near the divertor target plate in DIII-D

Strong impacts of drifts on the divertor plasma in–out asymmetry and detachment are demonstrated in DIII-D with an open divertor configuration. For forward toroidal field, BT, i.e., with the ion B × ∇B drift toward the divertor, the particle flux to the inner divertor, as represented by the Langmuir probe measured ion saturation current (Jsat), exhibits a double peak structure, with electron temperature, lower at the inner target. Reversing the BT direction reverses both the radial and poloidal E × B flows, leading to a broad particle flux profile in the outboard scrape-off layer (SOL) with a similar double-peak structure to that observed at the inner target with forward BT. The correlation of a double peak structure with divertor temperature profiles confirms physical coupling between the drift flow and sheath boundary condition and their strong impact on divertor profiles. In addition, under reversed BT conditions, increasing the density flattens the target temperature profile. However, Jsat remains high away from the strike point, rendering it difficult to achieve an “effective” detached plasma, i.e., with effective reduction in both peak heat flux and peak temperature (in the far SOL). In contrast, divertor detachment with a cold and flat temperature profile can be achieved at both target plates with the forward BT.

Novel electric field effects on magneto-optical conductivity in eight-Pmmn borophene

We theoretically study the Landau levels and the magneto-optical conductivity of eight-Pmmn borophene in the presence of a perpendicular magnetic field and an inplane electric field. We find that in the absence of the inplane electric field, the magneto-optical conductivity of eight-Pmmn borophene presents a series of striking single resonance peaks as functions of the frequency ω, and the longitudinal conductivities are found to be anisotropic due to its anisotropic tilted Dirac cones. In the presence of the inplane electric field, some novel effects are predicted on the Landau levels and the magneto-optical conductivity. The Landau level spacings in the two tilted Dirac cones are different, which lifts the degeneracy of the twofold valley, and the magneto-optical conductivity appears a double peak structure. We also discuss the influence of the chemical potential between different Landau levels on the double peak of the magneto-optical response. The valley related magneto-optical properties in the anisotropic structure may make eight-Pmmn borophene a candidate for the new optical devices.

Statistical properties of group height and group length in combined sea states

The statistical properties of ocean wave groups are extremely important for the analysis of resonant effects on ships and marine structures. The patterns in combined sea states have attracted increasing attention recently. This study focuses on the probability distributions of the group height and group length as defined by an envelope approach in sea states with bimodal spectra. Wave data from laboratory experiments and numerical simulations are used. The envelope spectra in combined sea states might exhibit a double-peaked structure. Although the bimodal envelope spectrum has slight effect on the group height distribution, the group length might have a multimodal and broader distribution. As a result, the joint distribution might be characterised by a multimodal shape. Further, a mixed Weibull distribution of the marginal distributions of the group parameters and a mixed copula model of their bivariate distributions are constructed. For comparison, a conventional Weibull distribution and a single copula model are also applied to fit the distributions. The results suggest that the single models can be used only to fit the group height distribution. By contrast, the mixed models can provide satisfactory descriptions of both the marginal distributions and joint distributions.

Revealing thermally driven distortion of magnon dispersion by spin Seebeck effect in Gd3Fe5O12

We report a systematic study of the temperature and field dependences of the spin Seebeck effect (SSE) in a bilayer of $\mathrm{Pt}/{\mathrm{Gd}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$. An anomalous structure is observed in the magnetic field dependent measurements at temperatures between \ensuremath{\sim}60 and \ensuremath{\sim}210 K. Unlike the ordinary SSE signal originating from the bare magnons, which changes sign at \ensuremath{\sim}95 and \ensuremath{\sim}266 K, the sign of the anomalies remains unchanged with increasing temperature. Moreover, the anomalies are found to show a temperature-sensitive double-peak structure between \ensuremath{\sim}116 and \ensuremath{\sim}143 K. We attribute these anomalies to the contribution from the quasiparticles hybridized between the Gd moment dominated spin wave (\ensuremath{\alpha} mode) and the transversal acoustic phonon, known as the magnon polarons. Given that the magnon polaron induced anomalies occur at the field where the linear phonon dispersion is tangential to the magnon dispersion curve, we explain these rich phenomena by an increase of the group velocity of the \ensuremath{\alpha}-mode magnon with increasing temperature and the nonparabolic magnon dispersion of ${\mathrm{Gd}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$. Our results demonstrate that the magnon polaron induced SSE is helpful for the investigation of the magnon dispersion evolution with a simple transport approach.

An X-Ray Study of the White Dwarf Binary AR Scorpii

Abstract We report a study of X-ray emission from the white dwarf/M-type star binary system AR Scorpii using archival data taken in 2016–2020. It has been known that the X-ray emission is dominated by optically thin thermal plasma emission and its flux level varies significantly over the orbital phase. The X-ray emission also contains a component that modulates with the beat frequency between the white dwarf’s spin frequency and orbital frequency. In this new analysis, the 2020 data taken by NICER shows that the X-ray emission modulates with the spin frequency as well as with the beat frequency, indicating that part of the X-ray emission comes from the white dwarf’s magnetosphere. It is found that the signal of the spin frequency appears only at a specific orbital phase, while the beat signal appears over the orbital phase. We interpret the X-ray emission modulating with the spin frequency and the beat frequency as a result of synchrotron emission from electrons with smaller and larger pitch angles, respectively. In the long-term evolution, the beat pulse profile averaged over the orbital phase changes from a single-peak structure in 2016/2018 to a double-peak structure in 2020. The observed X-ray flux levels measured in 2016/2017 are higher than those measured in 2018/2020. The plasma temperature and the amplitude of the orbital waveform might vary with time too. These results indicate that the X-ray emission from AR Scorpii evolves on a timescale of years. This long-term evolution would be explained by a superorbital modulation related to, for example, a precession of the white dwarf or a fluctuation of the system related to the activity of the companion star.

Measurements of dihadron correlations relative to the event plane in Au+Au collisions at GeV * *Supported in part by the Offices of NP and HEP within the U.S. DOE Office of Science, the U.S. NSF, the Sloan Foundation, the DFG cluster of excellence ‘Origin and Structure of the Universe’ of Germany, CNRS/IN2P3, STFC and EPSRC of the United Kingdom, FAPESP

Dihadron azimuthal correlations containing a high transverse momentum ( ) trigger particle are sensitive to the properties of the nuclear medium created at RHIC through the strong interactions occurring between the traversing parton and the medium, i.e. jet-quenching. Previous measurements revealed a strong modification to dihadron azimuthal correlations in Au+Au collisions with respect to p+p and d+Au collisions. The modification increases with the collision centrality, suggesting a path-length or energy density dependence to the jet-quenching effect. This paper reports STAR measurements of dihadron azimuthal correlations in mid-central (20%-60%) Au+Au collisions at GeV as a function of the trigger particle's azimuthal angle relative to the event plane, . The azimuthal correlation is studied as a function of both the trigger and associated particle . The subtractions of the combinatorial background and anisotropic flow, assuming Zero Yield At Minimum (ZYAM), are described. The correlation results are first discussed with subtraction of the even harmonic (elliptic and quadrangular) flow backgrounds. The away-side correlation is strongly modified, and the modification varies with , with a double-peak structure for out-of-plane trigger particles. The near-side ridge (long range pseudo-rapidity correlation) appears to drop with increasing while the jet-like component remains approximately constant. The correlation functions are further studied with the subtraction of odd harmonic triangular flow background arising from fluctuations. It is found that the triangular flow, while responsible for the majority of the amplitudes, is not sufficient to explain the -dependence of the ridge or the away-side double-peak structure. The dropping ridge with could be attributed to a -dependent elliptic anisotropy; however, the physics mechanism of the ridge remains an open question. Even with a -dependent elliptic flow, the away-side correlation structure is robust. These results, with extensive systematic studies of the dihadron correlations as a function of , trigger and associated particle , and the pseudo-rapidity range , should provide stringent inputs to help understand the underlying physics mechanisms of jet-medium interactions in high energy nuclear collisions.