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B. Liu

Publications and source records attributed to B. Liu.

At least 37 records · Page 2Linked to original sources

Phase-Imaging Ion-Cyclotron-Resonance Mass Spectrometry with the Canadian Penning Trap at CARIBU

The Canadian Penning Trap mass spectrometer (CPT) has conducted precision mass measurements of neutron-rich nuclides from the CAlifornium Rare Isotope Breeder Upgrade (CARIBU) of the Argonne Tandem Linac Accelerator System (ATLAS) facility at Argonne National Laboratory using the Phase-Imaging Ion-Cyclotron-Resonance (PIICR) technique for over half a decade. Here we discuss the CPT system, and methods to improve accuracy and precision in mass measurement using PI-ICR including some optimization techniques and recently studied systematic effects.

physics.ins-det↗

Unusually Strong Four-Phonon Scattering Effects on Low-Temperature Thermal Conductivity in Two-Dimensional Materials

First principles-based predictions of lattice thermal conductivity (TC) from perturbation theory have achieved significant success. Usually, it only included three-phonon (3ph) scattering processes, only recently four-phonon (4ph) scattering processes were found to have a comparable impact as 3ph scattering at medium and high temperatures in various materials. While the influence of 4ph scattering on TC at low temperatures was generally believed to be insignificant. By combining the first-principles calculations, machine learning techniques, and Boltzmann transport equation (BTE), we find that there are unusually strong 4ph processes even in the low-frequency range of two-dimensional (2D) materials such as h-XN (X = B, Al, Ga), which have a remarkable influence on the low-temperature TC. Such strong 4ph processes originated from the out-of-plane acoustic (ZA) phonon mode of 2D materials. Furthermore, we find that the intensity of 4ph scattering and thus TC can be effectively manipulated by changing the dispersion of ZA phonon mode, which can be easily achieved through strain engineering. The present study provides new insights into low-temperature phonon transport and its manipulation in 2D materials.

cond-mat.mtrl-sci↗

Precise Mass Measurement of the Longest Odd-Odd Chain of \boldmath $1^+$ Ground States

Precise mass measurements of the ground and isomeric states of the odd-odd $^{108, 110, 112, 114, 116}$Rh were performed using the Canadian Penning Trap at Argonne National Laboratory, showing good agreement with recent JYFLTRAP measurements. A new possible isomeric state of $^{114}$Rh was also observed. These isotopes are part of the longest odd-odd chain of identical ground-state spin-parity assignment of 1$^+$, spanning $^{104-118}$Rh, despite being in a region of deformation. Realistic phenomenological mean-field calculations using ``universal'' Wood-Saxon Hamiltonian were performed, which explained this phenomenon for the first time. In addition, multi-quasiparticle blocking calculations were performed to study the configuration of low-lying states in the odd-odd Rh nuclei, elucidating anomalous isomeric yield ratio observed for $^{114}$Rh.

nucl-ex↗

High-Performance Nonvolatile Spin FETs from 2D Metallic Ferromagnetic and Ferroelectric Multiferroic Heterostructure

All-electric-controlled nonvolatile spin field-effect transistors (SFETs) based on two-dimensional (2D) multiferroic van der Waals (vdW) heterostructures hold great promise for advanced spintronics applications. However, their performance is hindered by the limited availability of 2D magnetic materials that can switch effectively between metallic and semiconducting states with sizable bandgaps controlled by ferroelectric polarization. Most studies have focused on materials that are naturally semiconducting, achieving a metallic state by modifying the ferroelectric polarization. In this work, we introduce an innovative approach that uses interface effects to convert inherently metallic 2D magnetic materials into half-metals and induce half-semiconducting behavior through changes in ferroelectric polarization. Density functional theory (DFT) calculations on the CrPS3/Sc2CO2 heterostructure demonstrate that the ferroelectric polarization of Sc2CO2 monolayers can adjust the electronic structure of CrPS3, enabling a switch from half-metallic to half-semiconducting states. Building on these insights, we designed a nonvolatile SFET and analyzed its transport properties using the nonequilibrium Green's function (NEGF) method combined with DFT. Our results show that reversing the ferroelectric polarization achieves an on/off current ratio exceeding 5000000%, and the heterostructure generates nearly 100% spin-polarized current with a current density of up to 6500 μA/μm at bias voltage below 0.2 V. These findings highlight a promising pathway for developing high-performance SFETs that surpass existing 2D heterojunction materials.

cond-mat.mtrl-sci↗

Upper Limit on the Photoproduction Cross Section of the Spin-Exotic $π_1(1600)$

The spin-exotic hybrid meson $π_{1}(1600)$ is predicted to have a large decay rate to the $ωππ$ final state. Using 76.6~pb$^{-1}$ of data collected with the GlueX detector, we measure the cross sections for the reactions $γp \to ωπ^+ π^- p$, $γp \to ωπ^0 π^0 p$, and $γp\toωπ^-π^0Δ^{++}$ in the range $E_γ=$ 8-10 GeV. Using isospin conservation, we set the first upper limits on the photoproduction cross sections of the $π^{0}_{1}(1600)$ and $π^{-}_{1}(1600)$. We combine these limits with lattice calculations of decay widths and find that photoproduction of $η'π$ is the most sensitive two-body system to search for the $π_1(1600)$.

nucl-ex↗

First Measurement of $a^0_2(1320)$ Polarized Photoproduction Cross Section

We measure for the first time the differential photoproduction cross section $dσ/dt$ of the $a_2(1320)$ meson at an average photon beam energy of 8.5~GeV, using data with an integrated luminosity of 104~pb$^{-1}$ collected by the GlueX experiment. We fully reconstruct the $γp \to ηπ^0 p$ reaction and perform a partial-wave analysis in the $a_2(1320)$ mass region with amplitudes that incorporate the linear polarization of the beam. This allows us to separate for the first time the contributions of natural- and unnatural-parity exchanges. These measurements provide novel information about the photoproduction mechanism, which is critical for the search for spin-exotic states.

nucl-ex↗

Test-time Controllable Image Generation by Explicit Spatial Constraint Enforcement

Recent text-to-image generation favors various forms of spatial conditions, e.g., masks, bounding boxes, and key points. However, the majority of the prior art requires form-specific annotations to fine-tune the original model, leading to poor test-time generalizability. Meanwhile, existing training-free methods work well only with simplified prompts and spatial conditions. In this work, we propose a novel yet generic test-time controllable generation method that aims at natural text prompts and complex conditions. Specifically, we decouple spatial conditions into semantic and geometric conditions and then enforce their consistency during the image-generation process individually. As for the former, we target bridging the gap between the semantic condition and text prompts, as well as the gap between such condition and the attention map from diffusion models. To achieve this, we propose to first complete the prompt w.r.t. semantic condition, and then remove the negative impact of distracting prompt words by measuring their statistics in attention maps as well as distances in word space w.r.t. this condition. To further cope with the complex geometric conditions, we introduce a geometric transform module, in which Region-of-Interests will be identified in attention maps and further used to translate category-wise latents w.r.t. geometric condition. More importantly, we propose a diffusion-based latents-refill method to explicitly remove the impact of latents at the RoI, reducing the artifacts on generated images. Experiments on Coco-stuff dataset showcase 30$\%$ relative boost compared to SOTA training-free methods on layout consistency evaluation metrics.

cs.CV↗

Front-end Replication Dynamic Window (FRDW) for Online Motor Imagery Classification

Motor imagery (MI) is a classical paradigm in electroencephalogram (EEG) based brain-computer interfaces (BCIs). Online accurate and fast decoding is very important to its successful applications. This paper proposes a simple yet effective front-end replication dynamic window (FRDW) algorithm for this purpose. Dynamic windows enable the classification based on a test EEG trial shorter than those used in training, improving the decision speed; front-end replication fills a short test EEG trial to the length used in training, improving the classification accuracy. Within-subject and cross-subject online MI classification experiments on three public datasets, with three different classifiers and three different data augmentation approaches, demonstrated that FRDW can significantly increase the information transfer rate in MI decoding. Additionally, FR can also be used in training data augmentation. FRDW helped win national champion of the China BCI Competition in 2022.

cs.HC↗

Efficient Electric Field Control of Magnetic Phase in Bilayer Magnets via interlayer hopping modulation

Two-dimensional (2D) van der Waals (vdW) magnets present a promising platform for spintronic applications due to their unique structural and electronic properties. The ability to electrostatically control their interlayer magnetic coupling between ferromagnetic and antiferromagnetic phases is particularly advantageous for the development of energy-efficient spintronic components. While effective in bilayer CrI3, achieving this control in other 2D magnets remains a challenge. In this work, we demonstrate that bilayer Cr2Ge2Te6 can achieve efficient electrostatic control through interlayer hopping modulation. We show that an external electric field can effectively manipulate the FM-AFM phase transition when interlayer hopping is enhanced by pressure or sliding. We further develop a four-site interlayer hopping model, revealing that the phase transition is driven by a combined effect of on-site energy splitting and interlayer electronic hopping. These findings pave the way for designing novel, electrically tunable spintronic devices, offering substantial potential for energy-efficient information processing and storage.

cond-mat.mes-hall↗

Mass measurements of neutron-rich nuclides using the Canadian Penning Trap to inform predictions in the $r$-process rare-earth peak region

Studies aiming to determine the astrophysical origins of nuclei produced by the rapid neutron capture process ($r$ process) rely on nuclear properties as inputs for simulations. The solar abundances can be used as a benchmark for such calculations, with the $r$-process rare-earth peak (REP) around mass number ($A$) 164 being of special interest due to its presently unknown origin. With the advancement of rare isotope beam production over the last decade and improvement in experimental sensitivities, many of these REP nuclides have become accessible for measurement. Masses are one of the most critical inputs as they impact multiple nuclear properties, namely the neutron-separation energies, neutron capture rates, $β$-decay rates, and $β$-delayed neutron emission probabilities. In this work, we report masses of 20 neutron-rich nuclides (along the Ba, La, Ce, Pr, Nd, Pm, Gd, Dy and Ho isotopic chains) produced at the CAlifornium Rare Isotope Breeder Upgrade (CARIBU) facility at Argonne National Laboratory. The masses were measured with the Canadian Penning trap (CPT) mass spectrometer using the Phase-Imaging Ion-Cyclotron-Resonance (PI-ICR) technique. We then use these new masses along with previously published CPT masses to inform predictions for a Markov Chain Monte Carlo (MCMC) procedure aiming to identify the astrophysical conditions consistent with both solar data and mass measurements. We show that the MCMC responds to this updated mass information, producing refined results for both mass predictions and REP abundances.

nucl-ex↗

Investigating the effects of precise mass measurements of Ru and Pd isotopes on machine learning mass modeling

Atomic masses are a foundational quantity in our understanding of nuclear structure, astrophysics and fundamental symmetries. The long-standing goal of creating a predictive global model for the binding energy of a nucleus remains a significant challenge, however, and prompts the need for precise measurements of atomic masses to serve as anchor points for model developments. We present precise mass measurements of neutron-rich Ru and Pd isotopes performed at the Californium Rare Isotope Breeder Upgrade facility at Argonne National Laboratory using the Canadian Penning Trap mass spectrometer. The masses of $^{108}$Ru, $^{110}$Ru and $^{116}$Pd were measured to a relative mass precision $δm/m \approx 10^{-8}$ via the phase-imaging ion-cyclotron-resonance technique, and represent an improvement of approximately an order of magnitude over previous measurements. These mass data were used in conjunction with the physically interpretable machine learning (PIML) model, which uses a mixture density neural network to model mass excesses via a mixture of Gaussian distributions. The effects of our new mass data on a Bayesian-updating of a PIML model are presented.

nucl-ex↗

Precise Mass Measurements of $A=133$ Isobars with the Canadian Penning Trap: Resolving the $Q_{β^-}$ anomaly at $^{133}$Te

We report precision mass measurements of $^{133}$Sb, $^{133g,m}$Te, and $^{133g,m}$I, produced at CARIBU at Argonne National Laboratory's ATLAS facility and measured using the Canadian Penning Trap mass spectrometer. These masses clarify an anomaly in the $^{133}$Te $β$-decay. The masses reported in the 2020 Atomic Mass Evaluation (M. Wang et al., 2021) produce $Q_{β^-}(^{133}$Te)=2920(6) keV; however, the highest-lying $^{133}$I level populated in this decay is observed at $E_i=2935.83(15)$ keV, resulting in an anomalous $Q_{β^{-}}^{i}=-16(6)$~keV. Our new measurements give $Q_{β^-}(^{133}\text{Te})=2934.8(11)$ keV, a factor of five more precise, yielding $Q{_β^i}=-1.0(12)$~keV, a 3$σ$ shift from the previous results. This resolves this anomaly, but indicates further anomalies in our understanding of the structure of this isotope.

nucl-ex↗

Measurement of Spin-Density Matrix Elements in $Δ^{++}(1232)$ photoproduction

We measure the spin-density matrix elements (SDMEs) of the $Δ^{++}(1232)$ in the photoproduction reaction $γp \to π^-Δ^{++}(1232)$ with the GlueX experiment in Hall D at Jefferson Lab. The measurement uses a linearly--polarized photon beam with energies from $8.2$ to $8.8$~GeV and the statistical precision of the SDMEs exceeds the previous measurement by three orders of magnitude for the momentum transfer squared region below $1.4$ GeV$^2$. The data are sensitive to the previously undetermined relative sign between couplings in existing Regge-exchange models. Linear combinations of the extracted SDMEs allow for a decomposition into natural and unnatural--exchange amplitudes. We find that the unnatural exchange plays an important role in the low momentum transfer region.

nucl-ex↗

Nontrivial impact of interlayer coupling on thermal conductivity: opposing trends in in-plane and out-of-plane phonons

The study of heat transport in two-dimensional (2D) materials reveals novel behaviors due to quantum confinement effects, where in-plane and out-of-plane phonons play crucial roles. In 2D materials like graphene, it is widely recognized that the out-of-plane vibrational mode is the primary contributor to thermal conductivity owing to the mirror symmetry. Based on this perspective, the introduction of interlayer coupling, which breaks this symmetry, is expected to induce a significant reduction in thermal conductivity within 2D materials. Nevertheless, recent studies have presented unexpected findings, indicating that interlayer coupling can actually increase thermal conductivity of 2D materials. This controversial result suggests a nontrivial underlying mechanism governing the effects of interlayer coupling on thermal conductivity in 2D materials, necessitating further exploration. In our work, we investigate the modulation of thermal conductivity through interlayer coupling in a sandwich structure composed of hexagonal boron nitride (h-BN) and bilayer graphene (BG), specifically a h- BN/BG/h-BN system. Through molecular dynamics simulations, we find that the thermal conductivity from out-of-plane phonons can be significantly reduced, while that from in-plane phonons can be significantly increased, as the interlayer coupling strength increases. This results in a nontrivial, coupling-strength-dependent overall thermal conductivity. The phonon spectrum analysis conducted using our modified package reveals that the upshift and flattening of the out-of-plane (ZA and ZO) phonon modes are mainly responsible for these variations, and the extent of the upshift and flattening is proportional to the strength of interlayer coupling. This work offers new insights into manipulating the thermal conductivity of 2D materials.

cond-mat.mes-hall↗

Quantum Clock Synchronization Network with Silicon-chip Dual-Pumped Entangled Photon Source

In this paper, we propose a quantum clock synchronization (QCS) network scheme with silicon-chip dual-pumped entangled photon source. This scheme couples two pump beams into the silicon-based waveguide, where degenerate and non-degenerate spontaneous four-wave mixing (SFWM) occurs, generating entanglement between one signal channel and three idler channels. The entangled photons are distributed to remote users through the wavelength division multiplexing strategy to construct an entanglement distribution network, and the round-trip QCS is adopted to realize a QCS network that can serve multiple users. A proof-of-principle QCS network experiment is implemented among the server and multiple users (Alice, Bob, and Charlie) for 11.1 hours, where Alice and Charlie are 10 km away from the server and Bob is 25 km away from the server. The lowest time deviations (TDEV) between the server and each user (Alice, Bob, and Charlie) are 1.57 ps, 0.82 ps and 2.57 ps at the average time of 8000 s, 8000 s and 800 s respectively. The results show that the QCS network scheme with dual-pumped SFWM photon source proposed by us achieves high accuracy, and the channel resources used by n users are reduced by about 30% compared with other round-trip QCS schemes.

quant-ph↗

Measurement of the J/$ψ$ photoproduction cross section over the full near-threshold kinematic region

We report the total and differential cross sections for $J/ψ$ photoproduction with the large acceptance GlueX spectrometer for photon beam energies from the threshold at 8.2~GeV up to 11.44~GeV and over the full kinematic range of momentum transfer squared, $t$. Such coverage facilitates the extrapolation of the differential cross sections to the forward ($t = 0$) point beyond the physical region. The forward cross section is used by many theoretical models and plays an important role in understanding $J/ψ$ photoproduction and its relation to the $J/ψ-$proton interaction. These measurements of $J/ψ$ photoproduction near threshold are also crucial inputs to theoretical models that are used to study important aspects of the gluon structure of the proton, such as the gluon Generalized Parton Distribution (GPD) of the proton, the mass radius of the proton, and the trace anomaly contribution to the proton mass. We observe possible structures in the total cross section energy dependence and find evidence for contributions beyond gluon exchange in the differential cross section close to threshold, both of which are consistent with contributions from open-charm intermediate states.

nucl-ex↗

Measurement of Spin-Density Matrix Elements in $ρ(770)$ Production with a Linearly Polarized Photon Beam at $E_γ= 8.2\,-\,8.8\,\text{GeV}$

The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized $8.5\,\text{GeV}$ photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson $ρ$(770). The statistical precision achieved exceeds that of previous experiments for polarized photoproduction in this energy range by orders of magnitude. We confirm a high degree of $s$-channel helicity conservation at small squared four-momentum transfer $t$ and are able to extract the $t$-dependence of natural and unnatural-parity exchange contributions to the production process in detail. We confirm the dominance of natural-parity exchange over the full $t$ range. We also find that helicity amplitudes in which the helicity of the incident photon and the photoproduced $ρ(770)$ differ by two units are negligible for $-t<0.5\,\text{GeV}^{2}/c^{2}$.

nucl-ex↗

Assessing Proton-Boron Fusion Feasibility under non-Thermal Equilibrium Conditions: Rider's Inhibition Revisited

Compared to the D-T reaction, the neutron-free proton-boron (p-$^{11}$B) fusion has garnered increasing attention in recent years. However, significant Bremsstrahlung losses pose a formidable challenge in p-$^{11}$B plasmas in achieving $Q>1$ in thermal equilibrium. The primary aim of this study is to corroborate Todd H. Rider's seminal work in the 1997 Physics of Plasmas, who investigated the feasibility of sustaining p-$^{11}$B fusion under non-thermal equilibrium conditions. Employing a series of simulations with new fusion cross-section, we assessed the minimum recirculating power that must be recycled to maintain the system's non-thermal equilibrium and found that it is substantially greater than the fusion power output, aligning with Rider's conclusions, whether under the conditions of non-Maxwellian electron distribution or Maxwellian electron distribution, reactors reliant on non-equilibrium plasmas for p-$^{11}$B fusion are unlikely to achieve net power production without the aid of highly efficient external heat engines. However, maintaining the ion temperature at 300 keV and the Coulomb logarithm at 15, while increasing the electron temperature beyond 23.33 keV set by Rider, leads to diminished electron-ion energy transfer and heightened Bremsstrahlung radiation. When the electron temperature approaches approximately 140 keV, this progression ultimately leads to a scenario where the power of Bremsstrahlung loss equals the power of electron-ion interactions, yet remains inferior to the fusion power. Consequently, this results in a net gain in energy production.

physics.plasm-ph↗