arXiv subjects

Q. He

Publications and source records attributed to Q. He.

At least 19 recordsLinked to original sources

arXiv2023

Epitaxial growth and scanning tunneling microscopy of LiV$_2$O$_4$ thin films on SrTiO$_3$(111)

LiV$_2$O$_4$ is a mixed-valent spinel oxide and one of a few transition-metal compounds to host a heavy fermion phase at low temperatures. While numerous experimental studies have attempted to elucidate how its 3$d$ electrons undergo giant mass renormalization, spectroscopic probes that may provide crucial hints, such as scanning tunneling microscopy (STM), remain to be applied. A prerequisite is atomically flat and pristine surfaces, which, in the case of LiV$_2$O$_4$, are difficult to obtain by cleavage of small, three-dimensional crystals. We report the epitaxial growth of LiV$_2$O$_4$ thin films with bulklike properties on SrTiO$_3$(111) via pulsed laser deposition and stable STM imaging of the LiV$_2$O$_4$(111) surface. The as-grown films were transferred $ex$ $situ$ to a room-temperature STM, where subsequent annealing with optional sputtering in ultrahigh vacuum enabled compact islands with smooth surfaces and a hexagonal 1$\times$1 atomic lattice to be resolved. Our STM measurements provide insights into growth mechanisms of LiV$_2$O$_4$ on SrTiO$_3$(111), as well as demonstrate the feasibility of performing surface-sensitive measurements of this heavy fermion compound.

cond-mat.mtrl-sci↗

arXiv2022

Coherent photoproduction of the neutral pion and eta meson on the deuteron at incident energies below 1.15 GeV

Coherent photoproduction of the neutral pion and eta meson on the deuteron, $\gamma{d}${$\to$}$\pi^0\eta{d}$, has been experimentally studied at incident photon energies ranging from the reaction threshold to 1.15 GeV. The total cross section demonstrates a rapid rise below 1 GeV. The data are underestimated by the existing theoretical calculations based on quasi-free $\pi^0 \eta$ photoproduction on the nucleon followed by deuteron coalescence. At the same time, the data are rather well reproduced by the calculations taking into account the final-state interaction. We have also measured for the first time the differential cross sections: the $\pi^0 \eta$ invariant-mass distribution $d\sigma/dM_{\pi \eta}$, the $\pi^0 d$ invariant-mass distribution $d\sigma/dM_{\pi d}$, the $\eta d$ invariant-mass distribution $d\sigma/dM_{\eta d}$, and the distribution over the deuteron emission angle $d\sigma/d\Omega_d$ in the overall center-of-mass frame. The measured cross section $d\sigma/d\Omega_d$ does not exhibit strongly backward-peaking behavior predicted by the calculations. At all incident energies, an increase in $d\sigma/dM_{\eta d}$ near the $\eta d$ threshold is observed, which indicates a bound or virtual $\eta d$ state resulting from a strong attraction between $\eta$ and a deuteron. The possibilities of using coherent $\pi^0\eta$ photoproduction on a nucleus to study the $\eta$-nuclear interaction are also discussed.

nucl-ex↗

arXiv2021

In Vivo Assessment of Hypertensive Nephrosclerosis Using Ultrasound Localization Microscopy

Purpose: As a typical chronic kidney disease (CKD), hypertensive nephrosclerosis (HN) is a common syndrome of hypertension, characterized by chronic kidney microvascular damage. Early diagnosis of microvascular damage using conventional ultrasound imaging encounters challenges in sensitivity and specificity owing to the inherent diffraction limit. Ultrasound localization microscopy (ULM) has been developed to obtain microvasculature and microvascular hemodynamics within the kidney, and would be a promising tool for early diagnosis of CKD. Methods: In this study, the advantage of ULM over conventional clinical inspection (serum and urine tests) and ultrasound imaging (Doppler and contrast-enhanced ultrasound imaging) for early diagnosis of HN was investigated. Examinations were carried out on 6 spontaneously hypertensive rats (SHR) and 5 normal Wistar-Kyoto (WKY) rats at the age of 10 weeks. Results: The experimental results showed that the indicators derived from conventional clinical inspection and ultrasound imaging (PSV, EDV, RI, RT, IMAX, mTT and AUC) did not show significant difference between hypertensive and healthy rats (p > 0.05), while the TTP derived from CEUS (p < 0.05) and the mean blood flow speed in artery of SHR derived from ULM is significantly higher than that of WKY rats (p < 0.01). Conclusion: The quantitative results showed that ULM has higher sensitivity than conventional clinical inspection and ultrasound imaging. ULM may promise a reliable solution for early diagnosis of HN.

physics.med-ph↗

arXiv2021

Study of quasi-particle dynamics using the optical pulse response of asuperconducting resonator

We study the optical pulse response of a superconducting half-wavelength coplanar waveguide (CPW) resonator. We apply a short optical pulse to the center strip of the CPW resonator, where the current distribution shows antinodes or nodes for different resonance modes, and measure the frequency response. We develop a time-dependent variable inductance circuit model with which we can simulate the optical pulse response of the resonator. By fitting this model to experimental data, we extract the temporal kinetic inductance variations, which directly reflect the quasi-particle recombination with time and diffusion in space. We also retrieve the spatial size of the quasi-particle distribution and the quasi-particle diffusion constant. Our study is very useful for the design of photon-counting kinetic inductance detectors, and the method developed in this work provides a useful way to study the quasi-particle dynamics in the superconductor.

cond-mat.supr-con↗

arXiv2021

Resonance-like structure near the $\eta d$ threshold in the $\gamma{d}${$\to$}$\pi^0\eta{d}$ reaction

To investigate the interaction between the nucleon $N$ and nucleon resonance $N(1535)1/2^-$, the $\eta d$ threshold structure connected to the isoscalar $S$-wave $N$-$N(1535)1/2^-$ system has been experimentally studied in the $\gamma{d}${$\to$}$\pi^0\eta{d}$ reaction at incident photon energies ranging from the reaction threshold to 1.15 GeV. A strong enhancement is observed near the $\eta d$ threshold over the three-body phase-space contribution in the $\eta d$ invariant-mass distribution. An analysis incorporating the known isovector resonance $\mathcal{D}_{12}$ with a spin-parity of $2^+$ in the $\pi^0d$ channel reveals the existence of a narrow isoscalar resonance-like structure with $1^-$ in the $\eta d$ system. Using a Flatt\'e parametrization, the mass is found to be $2.427_{-0.006}^{+0.013}$ GeV, close to the $\eta d$ threshold, and the width is $\left(0.029_{-0.029}^{+0.006}{\rm\ GeV}\right)+\left(0.00_{-0.00}^{+0.41}\right) p_\eta c$, where $p_\eta$ denotes the $\eta$ momentum in the rest frame of the $\eta d$ system. The observed structure would be attributed to a predicted isoscalar $1^-$ $\eta NN$ bound state from $\eta NN$ and $\pi NN$ coupled-channel calculation, or an $\eta d$ virtual state owing to strong $\eta d$ attraction.

nucl-ex↗

arXiv2020

Tunneling-tip-induced collapse of the charge gap in the excitonic insulator Ta$_2$NiSe$_5$

Tuning many-body electronic phases by an external handle is of both fundamental and practical importance in condensed matter science. The tunability mirrors the underlying interactions, and gigantic electric, optical and magnetic responses to minute external stimuli can be anticipated in the critical region of phase change. The excitonic insulator is one of the exotic phases of interacting electrons, produced by the Coulomb attraction between a small and equal number of electrons and holes, leading to the spontaneous formation of exciton pairs in narrow-gap semiconductors/semimetals. The layered chalcogenide Ta$_2$NiSe$_5$ has been recently discussed as such an excitonic insulator with an excitation gap of ~250 meV below $T_c$ = 328 K. Here, we demonstrate a drastic collapse of the excitation gap in Ta$_2$NiSe$_5$ and the realization of a zero-gap state by moving the tip of a cryogenic scanning tunneling microscope towards the sample surface by a few angstroms. The collapse strongly suggests the many-body nature of the gap in the insulating state of Ta$_2$NiSe$_5$, consistent with the formation of an excitonic state. We argue that the collapse of the gap is driven predominantly by the electrostatic charge accumulation at the surface induced by the proximity of the tip and the resultant carrier doping of the excitonic insulator. Our results establish a novel phase-change function based on excitonic insulators.

cond-mat.str-el↗

arXiv2020

Measuring intensity interference in a low multiplicity system $\pi \pi x$ with a new observing method

Prior proposed observing approaches using event mixing technique for Bose-Einstein correlations (BEC) measurements in exclusive reactions with very low multiplicities are still unsatisfactory due to the problems of sample reduction and introducing extra and unnecessary fitting parameters. We here propose an event mixing method with a new mixing cut, named energy sum range (ESR) cut, to investigate two-pion Bose-Einstein correlations (BEC) in reactions with only two identical pions among three final state particles. This mixing method employs two-pion energy sum characteristic to control the mixing procedures, with no requirement on eliminating any original events. Numerical simulations are performed to show the viability of this new BEC observing method.

nucl-th↗

arXiv2019

$\omega N$ scattering length from $\omega$ photoproduction on the proton near the threshold

Photoproduction of the $\omega$ meson on the proton has been experimentally studied near the threshold. The total cross sections are determined at incident energies ranging from 1.09 to 1.15 GeV. The 1/2 and 3/2 spin-averaged scattering length $a_{\omega p}$ and effective range $r_{\omega p}$ between the $\omega$ meson and proton are estimated from the shape of the total cross section as a function of the incident photon energy: $a_{\omega p} = \left(-0.97^{+0.16_{\rm stat}}_{-0.16_{\rm stat}}{}^{+0.03_{\rm syst}}_{-0.00_{\rm syst}}\right)+i \left(0.07^{+0.15_{\rm stat}}_{-0.14_{\rm stat}}{}^{+0.17_{\rm syst}}_{-0.09_{\rm syst}}\right)$ fm and $r_{\omega p}=\left(+2.78^{+0.68_{\rm stat}}_{-0.54_{\rm stat}}{}^{+0.11_{\rm syst}}_{-0.13_{\rm syst}}\right)+i\left(-0.01^{+0.46_{\rm stat}}_{-0.50_{\rm stat}}{}^{+0.07_{\rm syst}}_{-0.00_{\rm syst}}\right)$ fm, resulting in a repulsive force. The real and imaginary parts for $a_{\omega p}$ and $r_{\omega p}$ are determined separately for the first time. A small $P$-wave contribution does not affect the obtained values.

nucl-ex↗

arXiv2018

An event mixing method with invariant-mass/energy hierarchy correspondence cut for Bose-Einstein correlations in $\pi \pi X$ system

A new event mixing constraint, namely invariant-mass/energy hierarchy correspondence (IMEHC) cut, is introduced for the low-multiplicity event mixing technique for the purpose of measuring Bose-Einstein correlations (BEC) in exclusive reactions with $\pi \pi X$ final state particles.The mixing cut is relevant to the hierarchy of the invariant mass of $\pi X$ system and two bosons energy hierarchy. Numerical tests are performed to check the validity of the new mixing method. As long as the measurements of BEC parameters $r_0$ and $\lambda_2$ are considered, this new mixing method is effective to observe BEC effects and the systematic bias of $r_0$ and $\lambda_2$ are smaller than the previously proposed mixing cut.

nucl-ex↗

arXiv2018

Non-strange Dibaryon Resonances Observed in the $\gamma d\to \pi^0\pi^0 d$ Reaction

Coherent double neutral-pion photoproduction on the deuteron, $\gamma{d}${$\to$}$\pi^0\pi^0{d}$, has been experimentally studied at incident photon energies ranging from 0.75 to 1.15 GeV. The total cross section as a function of the $\gamma{d}$ center-of-mass energy shows resonance-like behavior, which peaks at approximately 2.47 and 2.63 GeV. The measured angular distribution of deuteron emission is rather flat, which cannot be reproduced by the kinematics of quasi-free $\pi^0\pi^0$ production with deuteron coalescence. In $\pi^0d $ invariant-mass distributions, a clear peak is observed at $2.14{\pm}0.01$ GeV$/c^2$ with a width of $0.09{\pm}0.01$ GeV$/c^2$. The spin-parity of this state is restricted to $1^+$, $2^+$ or $3^-$ from the angular distributions of the two $\pi^0$s. The present work shows strong evidence for the existence of an isovector dibaryon resonance with a mass of 2.14 GeV$/c^2$. The $2^+$ assignment is consistent with the theoretically predicted ${\cal{D}}_{12}$ state, and also with the energy dependence of the $\pi{d}$ partial-wave amplitude $^3\!P_2$ for the $\pi^{\pm}d${$\to$}$\pi^{\pm}d$ and $\pi^+d${$\to$}${pp}$ reactions.

nucl-ex↗

arXiv2017

A study of event mixing for two-pion Bose-Einstein correlations in the {\gamma}p -> {\pi}^0 {\pi}^0 p reaction

We develop an event mixing technique with a missing mass consistency (MMC) cut and a pion energy (PE) cut for the measurement of two-pion Bose-Einstein correlations (BEC) in reactions with only two identical pions produced in the final state. A multi mixing mode that allows one event to be mixed with multiple other events is proposed for the purpose of improving the statistics of mixed samples, and compared with the single mixing mode which requires one original event can be mixed only once. Numerical tests using the {\gamma}p -> {\pi}^0 {\pi}^0 p events are used to testify its ability to measure two-pion correlations. To improve the mixing speed, the optimal MMC cut window is also explored via simulations.

nucl-ex↗

arXiv2016

First measurement of coherent double neutral-pion photoproduction on the deuteron at incident energies below 0.9 GeV

The total cross sections were measured for coherent double neutral-pion photoproduction on the deuteron at incident energies below 0.9 GeV for the first time. No clear resonance-like behavior is observed in the excitation function for $W_{\gamma d}=2.38$--2.61 GeV, where the $d^*(2380)$ dibaryon resonance observed at COSY is expected to appear. The measured excitation function is consistent with the existing theoretical calculation for this reaction. The upper limit of the total cross section is found to be $0.034$~$\mu$b for the dibaryon resonance at $W_{\gamma d}=2.37$~GeV (90\% confidence level) in the $\gamma d \to \pi^0\pi^0 d$ reaction.

nucl-ex↗

arXiv2015

The Detector System of The Daya Bay Reactor Neutrino Experiment

The Daya Bay experiment was the first to report simultaneous measurements of reactor antineutrinos at multiple baselines leading to the discovery of $\bar{\nu}_e$ oscillations over km-baselines. Subsequent data has provided the world's most precise measurement of $\rm{sin}^22\theta_{13}$ and the effective mass splitting $\Delta m_{ee}^2$. The experiment is located in Daya Bay, China where the cluster of six nuclear reactors is among the world's most prolific sources of electron antineutrinos. Multiple antineutrino detectors are deployed in three underground water pools at different distances from the reactor cores to search for deviations in the antineutrino rate and energy spectrum due to neutrino mixing. Instrumented with photomultiplier tubes (PMTs), the water pools serve as shielding against natural radioactivity from the surrounding rock and provide efficient muon tagging. Arrays of resistive plate chambers over the top of each pool provide additional muon detection. The antineutrino detectors were specifically designed for measurements of the antineutrino flux with minimal systematic uncertainty. Relative detector efficiencies between the near and far detectors are known to better than 0.2%. With the unblinding of the final two detectors' baselines and target masses, a complete description and comparison of the eight antineutrino detectors can now be presented. This paper describes the Daya Bay detector systems, consisting of eight antineutrino detectors in three instrumented water pools in three underground halls, and their operation through the first year of eight detector data-taking.

physics.ins-det↗

arXiv2015

Fast and Rigorous DC Solution in Finite Element Method for Integrated Circuit Analysis

Large scale circuit simulation, such as power delivery network analysis, has become increasingly challenge in the VLSI design verification flow. Power delivery network can be simulated by both SPICE-type circuit-based model and eletromagnetics-based model when full-wave accuracy is desired. In the early time of the time domain finite element simulation for integrated circuit, the modes having the highest eigenvalues supported by the numerical system will be excited. Because of the band limited source, after the early time, the modes having a resonance frequency well beyond the input frequency band will die down, and all physically important high-order modes and DC mode will show up and become dominant. Among these modes, the DC mode is the last one to show up. Although the convergence criterion is not applied on the DC mode, the existence of DC mode in the field solution will deteriorate the convergence rate of the first several high order modes. Therefore, this paper first analyzed the mathematic characteristics of the DC mode and proposed a rigorous and fast solution to extract the DC mode from the numerical system in order to speed up the convergence rate. Experimental results demonstrated the robustness and superior performance of this method.

cs.CE↗

arXiv2015

Room-temperature antiferromagnetic memory resistor

The bistability of ordered spin states in ferromagnets (FMs) provides the magnetic memory functionality. Traditionally, the macroscopic moment of ordered spins in FMs is utilized to write information on magnetic media by a weak external magnetic field, and the FM stray field is used for reading. However, the latest generation of magnetic random access memories demonstrates a new efficient approach in which magnetic fields are replaced by electrical means for reading and writing. This concept may eventually leave the sensitivity of FMs to magnetic fields as a mere weakness for retention and the FM stray fields as a mere obstacle for high-density memory integration. In this paper we report a room-temperature bistable antiferromagnetic (AFM) memory which produces negligible stray fields and is inert in strong magnetic fields. We use a resistor made of an FeRh AFM whose transition to a FM order 100 degrees above room-temperature, allows us to magnetically set different collective directions of Fe moments. Upon cooling to room-temperature, the AFM order sets in with the direction the AFM moments pre-determined by the field and moment direction in the high temperature FM state. For electrical reading, we use an antiferromagnetic analogue of the anisotropic magnetoresistance (AMR). We report microscopic theory modeling which confirms that this archetypical spintronic effect discovered more than 150 years ago in FMs, can be equally present in AFMs. Our work demonstrates the feasibility to realize room-temperature spintronic memories with AFMs which greatly expands the magnetic materials base for these devices and offers properties which are unparalleled in FMs.

cond-mat.mtrl-sci↗

arXiv2012

Improved Measurement of Electron Antineutrino Disappearance at Daya Bay

We report an improved measurement of the neutrino mixing angle $θ_{13}$ from the Daya Bay Reactor Neutrino Experiment. We exclude a zero value for $\sin^22θ_{13}$ with a significance of 7.7 standard deviations. Electron antineutrinos from six reactors of 2.9 GW$_{\rm th}$ were detected in six antineutrino detectors deployed in two near (flux-weighted baselines of 470 m and 576 m) and one far (1648 m) underground experimental halls. Using 139 days of data, 28909 (205308) electron antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to the expected number of antineutrinos assuming no oscillations at the far hall is $0.944\pm 0.007({\rm stat.}) \pm 0.003({\rm syst.})$. An analysis of the relative rates in six detectors finds $\sin^22θ_{13}=0.089\pm 0.010({\rm stat.})\pm0.005({\rm syst.})$ in a three-neutrino framework.

hep-ex↗

arXiv2012

Updated Measurement of the Strong Phase in D0 --> K+pi- Decay Using Quantum Correlations in e+e- --> D0 D0bar at CLEO

We analyze a sample of 3 million quantum-correlated D0 D0bar pairs from 818 pb^-1 of e+e- collision data collected with the CLEO-c detector at E_cm = 3.77 GeV, to give an updated measurement of \cos\delta and a first determination of \sin\delta, where \delta is the relative strong phase between doubly Cabibbo-suppressed D0 --> K+pi- and Cabibbo-favored D0bar --> K+pi- decay amplitudes. With no inputs from other experiments, we find \cos\delta = 0.81 +0.22+0.07 -0.18-0.05, \sin\delta = -0.01 +- 0.41 +- 0.04, and |\delta| = 10 +28+13 -53-0 degrees. By including external measurements of mixing parameters, we find alternative values of \cos\delta = 1.15 +0.19+0.00 -0.17-0.08, \sin\delta = 0.56 +0.32+0.21 -0.31-0.20, and \delta = (18 +11-17) degrees. Our results can be used to improve the world average uncertainty on the mixing parameter y by approximately 10%.

hep-ex↗

arXiv2012

Observation of electron-antineutrino disappearance at Daya Bay

The Daya Bay Reactor Neutrino Experiment has measured a non-zero value for the neutrino mixing angle $θ_{13}$ with a significance of 5.2 standard deviations. Antineutrinos from six 2.9 GW$_{\rm th}$ reactors were detected in six antineutrino detectors deployed in two near (flux-weighted baseline 470 m and 576 m) and one far (1648 m) underground experimental halls. With a 43,000 ton-GW_{\rm th}-day livetime exposure in 55 days, 10416 (80376) electron antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to expected number of antineutrinos at the far hall is $R=0.940\pm 0.011({\rm stat}) \pm 0.004({\rm syst})$. A rate-only analysis finds $\sin^22θ_{13}=0.092\pm 0.016({\rm stat})\pm0.005({\rm syst})$ in a three-neutrino framework.

hep-ex↗