arXiv subjects

C. Wang

Publications and source records attributed to C. Wang.

At least 55 records · Page 3Linked to original sources

arXiv2025

Anomalies in the rotational spectra of $^{86}$Sr ULRRM dimers

Anomalies in the rotational structure of $^{86}$Sr $^3S_1$ dimer ultralong-range Rydberg molecules (ULRRMs) created in a cold strontium gas by two-photon excitation via the intermediate $5s5p~^3P_1$ state are reported. Measurements reveal that the distribution of product rotational states is sensitive to intermediate state detuning. Comparative studies using $^{84}$Sr $^1S_0$ and $^3S_1$, and $^{86}$Sr $^1S_0$ dimers display no similar behavior, indicating that the observed behavior is peculiar to $^{86}$Sr triplet dimers. While we have no definitive hypothesis as to the physical mechanism responsible for this behavior, possible explanations might involve the very different scattering lengths for $^{84}$Sr and $^{86}$Sr, or the interchange of spin and rotational angular momentum.

physics.atom-ph↗

arXiv2024

Pseudo-easy-axis anisotropy in antiferromagnetic $S=1$ diamond-lattice systems Ni$X_{2}$(pym)$_{2}$

We investigate the magnetic properties of $S=1$ antiferromagnetic diamond lattice, Ni$X_{2}$(pyrimidine)$_{2}$ ($X$ = Cl, Br), hosting a single-ion anisotropy (SIA) orientation which alternates between neighbouring sites. Through neutron diffraction measurements of the $X$ = Cl compound, the ordered state spins are found to align collinearly along a pseudo-easy-axis, a unique direction created by the intersection of two easy planes. Similarities in the magnetization, exhibiting spin-flop transitions, and the magnetic susceptibility in the two compounds imply that the same magnetic structure and a pseudo-easy-axis is also present for $X$ = Br. We estimate the Hamiltonian parameters by combining analytical calculations and Monte-Carlo (MC) simulations of the spin-flop and saturation field. The MC simulations also reveal that the spin-flop transition occurs when the applied field is parallel to the pseudo-easy-axis. Contrary to conventional easy-axis systems, there exist field directions perpendicular to the pseudo-easy-axis for which the magnetic saturation is approached asymptotically and no symmetry-breaking phase transition is observed at finite fields.

cond-mat.str-el↗

arXiv2024

Developing fractional quantum Hall states at $ν$ = $\dfrac{1}{7}$ and $\dfrac{2}{11}$ in the presence of significant Landau level mixing

Termination of the fractional quantum Hall states (FQHSs) and the emergence of Wigner crystal phases at very small Landau level filling factors ($ν$) have been of continued interest for decades. Recently, in ultra-high-quality, dilute GaAs 2D electron systems (2DESs), strong evidence was reported for FQHSs at $ν=1/7, 2/13$ and 2/11 which fall in the $ν= p/(6p\pm1)$ Jain series of FQHSs, interpreted as integer ($p = 1$, 2) QHSs of 6-flux composite fermions ($^6$CFs). These states are surrounded by strongly-insulating phases which are generally believed to be Wigner crystals. Here, we study an ultra-high-quality 2DES confined to an AlAs quantum well where the 2D electrons have a much larger effective mass ($m^*\simeq 0.45 m_e$) and a smaller dielectric constant ($ε\simeq10ε_0$) compared to GaAs 2D electrons ($m^*\simeq 0.067 m_e$ and $ε\simeq13ε_0$). This combination of $m^*$ and $ε$ renders the Landau level mixing parameter $κ$, defined as the ratio of the Coulomb and cyclotron energies, $\simeq 9$ times larger in AlAs 2DESs ($κ\propto m^*/ε$). Qualitatively similar to the GaAs 2DESs, we observe an insulating behavior reentrant around a strong $ν=1/5$ FQHS, and extending to $ν<1/5$. Additionally, we observe a clear minimum in magnetoresistance at $ν=2/11$, and an inflection point at $ν=1/7$ which is very reminiscent of the first report of an emerging FQHS at $ν=1/7$ in GaAs 2DESs. The data provide evidence for developing QHSs of $^6$CFs at very small fillings. This is very surprising because $κ$ near $ν\simeq 1/6$ in our sample is very large ($\simeq4$), and larger $κ$ has the tendency to favor Wigner crystal states over FQHSs at small fillings. Our data should inspire calculations that accurately incorporate $κ$ in competing many-body phases of $^6$CFs at extremely small fillings near $ν=1/6$.

cond-mat.str-el↗

arXiv2024

Elucidating the roles of collision energy and photon momentum transfer in the formation of ultralong-range Rydberg molecules

Spectroscopic measurements of the rotational distribution of $^{84}$Sr and $^{86}$Sr 5sns $^1S_0$ ultralong-range Rydberg molecular dimers created via photoassociation in a cold gas are reported. The dimers are produced by two-photon excitation via the 5s5p $^1P_1$ intermediate state. The use of singlet states permits detailed study of the roles that the initial atom-atom interaction, photon momentum transfer during Rydberg excitation, and sample temperature play in determining the spectral lineshape and final dimer rotational distribution. The results are in good agreement with the predictions of a model that includes these effects. The present work further highlights the sensitivity of ultralong-range Rydberg molecule formation to the state of the initial cold gas.

physics.atom-ph↗

arXiv2024

Unified one-parameter scaling function for Anderson localization transitions in non-reciprocal non-Hermitian systems

By using dimensionless conductances as scaling variables, the conventional one-parameter scaling theory of localization fails for non-reciprocal non-Hermitian systems such as the Hanato-Nelson model. Here, we propose a one-parameter scaling function using the participation ratio as the scaling variable. Employing a highly accurate numerical procedure based on exact diagonalization, we demonstrate that this one-parameter scaling function can describe Anderson localization transitions of non-reciprocal non-Hermitian systems in one and two dimensions of symmetry classes AI and A. The critical exponents of correlation lengths depend on symmetries and dimensionality only, a typical feature of universality. Moreover, we derive a complex-gap equation based on the self-consistent Born approximation that can determine the disorder at which the point gap closes. The obtained disorders match perfectly the critical disorders of Anderson localization transitions from the one-parameter scaling function. Finally, we show that the one-parameter scaling function is also valid for Anderson localization transitions in reciprocal non-Hermitian systems such as two-dimensional class AII$^\dagger$ and can, thus, serve as a unified scaling function for disordered non-Hermitian systems.

cond-mat.dis-nn↗

arXiv2024

An absence of binary companions to Wolf-Rayet stars in the Small Magellanic Cloud: implications for mass loss and black hole masses at low metallicity

In order to predict the black hole mass distributions at high redshift, we need to understand whether very massive single stars ($M>40$ M$_\odot$) at low metallicity $Z$ lose their hydrogen-rich envelopes, like their metal-rich counterparts, or whether a binary companion is required to achieve this. To test this, we undertake a deep spectroscopic search for binary companions of the seven apparently single Wolf-Rayet (WR) stars in the Small Magellanic Cloud (SMC; $Z \simeq 1/5 Z_\odot$). For each of them, we acquired six high-quality VLT-UVES spectra spread over 1.5 years. By using the narrow N V lines in these spectra, we monitor radial velocity (RV) variations to search for binary motion. We find low RV variations between 6 and 23 km/s for the seven WR stars, with a median standard deviation of $5$ km/s. Our Monte Carlo simulations imply probabilities below ~5% for any of our target WR stars to have a binary companion more massive than ~5 M$_\odot$ at orbital periods of less than a year. We estimate that the probability that all our target WR stars have companions with orbital periods shorter than 10 yr is below ~10$^{-5}$, and argue that the observed modest RV variations may originate from intrinsic atmosphere or wind variability. Our findings imply that metal-poor massive stars born with $M \gtrsim 40$ M$_\odot$ can lose most of their hydrogen-rich envelopes via stellar winds or eruptive mass loss, which strongly constrains their initial mass - black hole mass relation. We also identify two of our seven target stars (SMC AB1 and SMC AB11) as runaway stars with a peculiar radial velocity of ~80 km/s. Moreover, with all five previously detected WR binaries in the SMC exhibiting orbital periods of below 20 d, a puzzling absence of intermediate-to-long-period WR binaries has emerged, with strong implications for the outcome of massive binary interaction at low metallicity.

astro-ph.SR↗

arXiv2024

Research on the Evaluation Index System of Enterprise Production Efficiency

This paper focuses on studying the evaluation index system for the production efficiency of tobacco enterprises. Considering the limitations of existing evaluation methods in accurately assessing the production quality of cigarette enterprises, a mathematical model based on the Analytic Hierarchy Process (AHP) is established. This model constructs an evaluation framework for the production efficiency of cigarette enterprises and subsequently analyzes the significance of each index within this framework. To comprehensively analyze the multi-index and feasibility aspects of the selected projects, the AHP method is employed to establish a comprehensive feasibility research and evaluation structure model. The result of this feasibility study provides the conclusion that the construction of an evaluation index system for the production efficiency of cigarette enterprises can indeed promote the enhancement of their production efficiency.

math.OC↗

arXiv2024

The FAST Galactic Plane Pulsar Snapshot Survey -- V. PSR J1901+0658 in a double neutron star system

Double neutron star (DNS) systems offer excellent opportunities to test gravity theories. We report the timing results of PSR J1901+0658, the first pulsar discovered in the FAST Galactic Plane Pulsar Snapshot (GPPS) Survey. Based on timing observations by FAST over 5 yr, we obtain the phase-coherent timing solutions and derive the precise measurements of its position, spin parameters, orbital parameters, and dispersion measure. It has a period of 75.7 ms, a period derivative of 2.169(6)$\times 10^{-19}$ s s$^{-1}$, and a characteristic age of 5.5 Gyr. This pulsar is in an orbit with a period of 14.45 d and an eccentricity of 0.366. One post-Keplerian parameter, periastron advance, has been well-measured as being 0.00531(9) deg yr$^{-1}$, from which the total mass of this system is derived to be 2.79(7) M$_{\odot}$. The pulsar has the mass upper limit of 1.68 M$_{\odot}$, so the lower limit for the companion mass is 1.11 M$_{\odot}$. Because PSR J1901+0658 is a partially recycled pulsar in an eccentric binary orbit with such a large companion mass, it should be in a DNS system according to the evolution history of the binary system.

astro-ph.HE↗

arXiv2024

Dwarf pulses of 10 pulsars detected by FAST

How pulsars radiate is a long-standing problem. Detailed polarization measurements of individual pulses shed light on currently unknown emission processes. Recently, based on supersensitive observations, dwarf pulses have been recognized as weak narrow pulses often appearing during the nulling state. In this study, we report the detection of dwarf pulses from ten pulsars, PSRs B0525+21, B1237+25, J1538+2345, J1824$-$0127, J1851$-$0053, B1901+10, J1939+10, B1944+17, B2000+40 and J2112+4058, based on observations conducted with the Five-hundred-meter Aperture Spherical radio Telescope. Dwarf pulses of five pulsars are clearly discernible in the two-dimensional distribution of pulse intensity and pulse width. For the other five pulsars, PSRs J1538+2345, J1824$-$0127, J1939+10, B2000+40, and J2112+4058, only a few dwarf pulses are detected from pulse stacks. The dwarf pulses can emerge in both cone and core emission components for PSR B1237+25, and the polarization angles of these dwarf pulses are mostly in the orthogonal polarization mode of normal pulses for PSR B1944+17. In general, pulsars with detected dwarf pulses tend to be located within the "death valley" region of the distribution of pulsar periods and period derivatives.

astro-ph.HE↗

arXiv2024

Signatures of correlated defects in an ultra-clean Wigner crystal in the extreme quantum limit

Low-disorder two-dimensional electron systems in the presence of a strong, perpendicular magnetic field terminate at very small Landau level filling factors in a Wigner crystal (WC), where the electrons form an ordered array to minimize the Coulomb repulsion. The nature of this exotic, many-body, quantum phase is yet to be fully understood and experimentally revealed. Here we probe one of WC's most fundamental parameters, namely the energy gap that determines its low-temperature conductivity, in record-mobility, ultra-high-purity, two-dimensional electrons confined to GaAs quantum wells. The WC domains in these samples contain $\simeq$ 1000 electrons. The measured gaps are a factor of three larger than previously reported for lower quality samples, and agree remarkably well with values predicted for the lowest-energy, intrinsic, hyper-corelated bubble defects in a WC made of flux-electron composite fermions, rather than bare electrons. The agreement is particularly noteworthy, given that the calculations are done for disorder-free composite fermion WCs, and there are no adjustable parameters. The results reflect the exceptionally high quality of the samples, and suggest that composite fermion WCs are indeed more stable compared to their electron counterparts.

cond-mat.mes-hall↗

arXiv2024

Experimental determination of the spin Hamiltonian of the cubic chiral magnet MnSi

A thorough description of the physics of a magnetic compound requires the validation of its microscopic spin Hamiltonian. Here, from the analysis of muon-spin rotation spectra recorded in the magnetically ordered state at low temperature in zero and finite magnetic fields, we determine the minimal Hamiltonian for the chiral binary intermetallic magnet MnSi, consistent with its high-temperature nonsymmorphic cubic space group P$2_1$3. The model provides constraints for the orientation of the Moriya vector characterizing the microscopic Dzyaloshinskii-Moriya interaction, with respect to the Mn nearest-neighbor bonds. Small twist and canting of the magnetic structure are revealed. Our result indicates that, within experimental uncertainties, the magnetoelastic coupling is not strong enough to lower the paramagnetic crystal symmetry in the magnetically ordered state. Additional implications from our work are discussed and complementary studies are suggested.

cond-mat.str-el↗

arXiv2024

Individual subpulses of PSR B1916+14 and their polarization properties

Individual subpulses of pulsars are regarded as the basic emission components, providing invaluable information to understand the radio emission process in the pulsar magnetosphere. Nevertheless, subpulses are overlapped with each other along the rotation phase for most pulsars, making it difficult to study the statistical properties of subpulses. Among the pulsars observed by the Five-hundred-meter Aperture Spherical radio Telescope, PSR B1916+14 has a large number of isolated well-resolved subpulses in the high time resolution observations, having a typical width of 0.15 ms and a high linear polarization. We find that the number distribution of subpulses contributes dominantly to the mean profile. According to the emission geometry, these emission units come from a region roughly 155 km above the polar cap in the pulsar magnetosphere, and the length scale of basic emission units is approximately 120 m. The deviations of polarization position angles for these single subpulses from the standard S-shaped curve are closely related to their fractional linear and circular polarization, and the large deviations tend to come from drifting subpulses.

astro-ph.HE↗

arXiv2023

Unusual magnetism of the axion-insulator candidate Eu$_5$In$_2$Sb$_6$

Eu$_5$In$_2$Sb$_6$ is a member of a family of orthorhombic nonsymmorphic rare-earth intermetallics that combines large localized magnetic moments and itinerant exchange with a low carrier density and perpendicular glide planes. This may result in special topological crystalline (wallpaper fermion) or axion insulating phases. Recent studies of Eu$_5$In$_2$Sb$_6$ single crystals have revealed colossal negative magnetoresistance and multiple magnetic phase transitions. Here, we clarify this ordering process using neutron scattering, resonant elastic X-ray scattering, muon spin-rotation, and magnetometry. The nonsymmorphic and multisite character of Eu$_5$In$_2$Sb$_6$ results in coplanar noncollinear magnetic structure with an Ising-like net magnetization along the $a$ axis. A reordering transition, attributable to competing ferro- and antiferromagnetic couplings, manifests as the onset of a second commensurate Fourier component. In the absence of spatially resolved probes, the experimental evidence for this low-temperature state can be interpreted either as an unusual double-$q$ structure or in a phase separation scenario. The net magnetization produces variable anisotropic hysteretic effects which also couple to charge transport. The implied potential for functional domain physics and topological transport suggests that this structural family may be a promising platform to implement concepts of topological antiferromagnetic spintronics.

cond-mat.str-el↗

arXiv2023

Ultraclean two-dimensional hole systems with mobilities exceeding 10$^7$ cm$^2$/Vs

Owing to their large effective mass, strong and tunable spin-orbit coupling, and complex band-structure, two-dimensional hole systems (2DHSs) in GaAs quantum wells provide rich platforms to probe exotic many-body physics, while also offering potential applications in ballistic and spintronics devices, and fault-tolerant topological quantum computing. We present here a systematic study of molecular-beam-epitaxy grown, modulation-doped, GaAs (001) 2DHSs where we explore the limits of low-temperature 2DHS mobility by optimizing two parameters, the GaAs quantum well width and the alloy fraction ($x$) of the flanking Al$_x$Ga$_{1-x}$As barriers. We obtain a breakthrough in 2DHS mobility, with a peak value $\simeq 18 \times 10^6$ cm$^2$/Vs at a density of 3.8 $\times$ 10$^{10}$ /cm$^{2}$, implying a mean-free-path of $\simeq 57 μ$m. Using transport calculations tailored to our structures, we analyze the operating scattering mechanisms to explain the non-monotonic evolution of mobility with density. We find it imperative to include the dependence of effective mass on 2DHS density, well width, and $x$. We observe concomitant improvement in quality as evinced by the appearance of delicate fractional quantum Hall states at very low density.

cond-mat.mes-hall↗

arXiv2023

Hyperfine structure of the $\mathbf{A^{1}Π}$ state of AlCl and its relevance to laser cooling and trapping

The majority of molecules proposed for laser cooling and trapping experiments have $Σ$-type ground states. Specifically, $^2Σ$ states have cycling transitions analogous to D1-lines in alkali-metal atoms while $^1Σ$ states offer both strong and weak cycling transitions analogous to those in alkaline-earth atoms. Despite this proposed variety, to date, only molecules with $^2Σ$-type ground states have successfully been confined and cooled in magneto-optical traps. While none of the proposed $^1Σ$-type molecules have been successfully laser cooled and trapped, they are expected to have various advantages in terms of exhibiting a lower chemical reactivity and an internal structure that benefits the cooling schemes. Here, we present the prospects and strategies for optical cycling in AlCl -- a $^1Σ$ molecule -- and report on the characterization of the $A^{1}Π$ state hyperfine structure. Based on these results, we carry out detailed simulations on the expected capture velocity of a magneto-optical trap for AlCl. Finally, using {\it ab initio} calculations, we identify the photodissociation via a $3^1Π$ state and photoionization process via the $3^1Σ^+$ state as possible loss mechanisms for a magneto-optical trap of AlCl.

physics.atom-ph↗

arXiv2023

Development of wide range photon detection system for muonic X-ray spectroscopy

We have developed a photon detection system for muonic X-ray spectroscopy. The detector system consists of high-purity germanium detectors with BGO Compton suppressors. The signals from the detectors are readout with a digital acquisition system. The absolute energy accuracy, energy and timing resolutions, photo-peak efficiency, the performance of the Compton suppressor, and high count rate durability are studied with standard $γ$-ray sources and in-beam experiment using $^{27}\mathrm{Al}(p, γ){}^{28}\mathrm{Si}$ resonance reaction. The detection system was demonstrated at Paul Scherrer Institute. A calibration method for a photon detector at a muon facility using muonic X-rays of $^{197}$Au and $^{209}$Bi is proposed.

physics.ins-det↗

arXiv2023

Anomalous hot electron generation from two-plasmon decay instability driven by broadband laser pulses with intensity modulations

We investigate the hot electrons generated from two-plasmon decay (TPD) instability driven by laser pulses with intensity modulated by a frequency $Δω_m$. Our primary focus lies on scenarios where $Δω_m$ is on the same order of the TPD growth rate $ γ_0$ ( $Δω_m \sim γ_0$), corresponding to moderate laser frequency bandwidths for TPD mitigation. With $Δω_m$ conveniently modeled by a basic two-color scheme of the laser wave fields in fully-kinetic particle-in-cell simulations, we demonstrate that the energies of TPD modes and hot electrons exhibit intermittent evolution at the frequency $Δω_m$, particularly when $Δω_m \sim γ_0$. With the dynamic TPD behavior, the overall ratio of hot electron energy to the incident laser energy, $f_{hot}$, changes significantly with $Δω_m$. While $f_{hot}$ drops notably with increasing $Δω_m$ at large $Δω_m$ limit as expected, it goes anomalously beyond the hot electron energy ratio for a single-frequency incident laser pulse with the same average intensity when $Δω_m$ falls below a specific threshold frequency $Δω_c$. We find this threshold frequency primarily depends on $γ_0$ and the collisional damping rate of plasma waves, with relatively lower sensitivity to the density scale length. We develop a scaling model characterizing the relation of $Δω_c$ and laser plasma conditions, enabling the potential extention of our findings to more complex and realistic scenarios.

physics.plasm-ph↗

arXiv2023

Wave packet dynamics and long-range tunneling within the SSH model using Rydberg-atom synthetic dimensions

Rydberg-atom synthetic dimensions in the form of a lattice of n$^3S_1$ levels, $58\leq n \leq 63$, coupled through two-photon microwave excitation are used to examine dynamics within the single-particle Su-Schrieffer-Heeger (SSH) Hamiltonian. This paradigmatic model of topological matter describes a particle hopping on a one-dimensional lattice with staggered hopping rates. Tunneling rates between lattice sites and on-site potentials are set by the microwave amplitudes and detuning, respectively. An atom is first excited to a Rydberg state that lies within the lattice and then subject to the microwave dressing fields. After some time, the dressing fields are turned off and the evolution of the population distribution in the different final lattice sites monitored using field ionization. The measurements show the existence of long-lived symmetry-protected edge states and reveal the existence of direct long-distance tunneling between the edge states. The results are in good agreement with model calculations and further demonstrate the potential of Rydberg-atom synthetic dimensions to simulate and faithfully reproduce complex Hamiltonians.

quant-ph↗