arXiv subjects

Y. Liu

Publications and source records attributed to Y. Liu.

At least 253 records · Page 14Linked to original sources

arXiv2021

Hourly Warning for Strong Earthquakes

A promising perspective is presented that humans can provide hourly warning for strong land earthquakes (EQs, Ms6). Two important atmospheric electrostatic signal features are described. A table that lists 9 strong land EQs with shock time, epicenter, magnitude, weather in the region near the epicenter, precursor beginning time, and precursor duration demonstrates that at approximately several hours to one day before a strong land EQ, the weather conditions are fair near the epicenter, and an abnormal negative atmospheric electrostatic signal is very obvious. Moreover, the mechanism is explained. A method by which someone could determine the epicenter and the magnitude of a forthcoming strong EQ is suggested. Finally, the possibility of realizing hourly warning for strong land EQs in the near future is pointed out.

physics.geo-ph↗

arXiv2021

Measurement of the cosmic ray helium energy spectrum from 70 GeV to 80 TeV with the DAMPE space mission

The measurement of the energy spectrum of cosmic ray helium nuclei from 70 GeV to 80 TeV using 4.5 years of data recorded by the DArk Matter Particle Explorer (DAMPE) is reported in this work. A hardening of the spectrum is observed at an energy of about 1.3 TeV, similar to previous observations. In addition, a spectral softening at about 34 TeV is revealed for the first time with large statistics and well controlled systematic uncertainties, with an overall significance of $4.3σ$. The DAMPE spectral measurements of both cosmic protons and helium nuclei suggest a particle charge dependent softening energy, although with current uncertainties a dependence on the number of nucleons cannot be ruled out.

astro-ph.HE↗

arXiv2021

Ferroelectric quantum criticality and enhanced superconductivity in plastically deformed strontium titanate

The properties of quantum materials are commonly tuned using experimental variables such as pressure, magnetic field and doping. Here we explore a different approach: irreversible, plastic deformation of single crystals. We show for the superconductor SrTiO$_3$ that compressive plastic deformation induces low-dimensional superconductivity significantly above the superconducting transition temperature ($T_c$) of undeformed samples, with evidence of superconducting correlations at temperatures two orders of magnitude above the bulk $T_c$. The superconductivity enhancement is correlated with the appearance of self-organized dislocation structures, as revealed by diffuse neutron and X-ray scattering. We also observe signatures of deformation-induced quantum-critical ferroelectric fluctuations and inhomogeneous ferroelectric order via Raman scattering. These results suggest that the strain surrounding the self-organized dislocation structures induces local ferroelectricity and quantum-critical dynamics that strongly influence $T_c$, consistent with a theory of superconductivity enhanced by soft polar fluctuations. More broadly, our results demonstrate the promise of plastic deformation and dislocation engineering as tools to manipulate electronic properties of quantum materials.

cond-mat.supr-con↗

arXiv2021

First experimental constraints on WIMP couplings in the effective field theory framework from CDEX

We present weakly interacting massive particles (WIMPs) search results performed using two approaches of effective field theory from the China Dark Matter Experiment (CDEX), based on the data from both CDEX-1B and CDEX-10 stages. In the nonrelativistic effective field theory approach, both time-integrated and annual modulation analyses were used to set new limits for the coupling of WIMP-nucleon effective operators at 90% confidence level (C.L.) and improve over the current bounds in the low $m_χ$ region. In the chiral effective field theory approach, data from CDEX-10 were used to set an upper limit on WIMP-pion coupling at 90% C.L. We for the first time extended the limit to the $m_χ<$ 6 GeV/$c^2$ region.

hep-ex↗

arXiv2021

Critical phenomena of the layered ferrimagnet Mn3Si2Te6 following proton irradiation

We examine the magnetic properties of the quasi 2D ferrimagnetic single crystal Mn3Si2Te6 (MST) through critical phenomena and magnetic entropy analysis in the easy axis (H || ab) as a function of proton irradiance. Employing a modified asymptotic analysis method, we find that upon proton irradiation the critical exponents do not fall into any particular universality class but lie close to mean field critical exponents (γ = 1, \b{eta} = 0.5). The presence of long-range interactions can be safely assumed for the pristine and irradiated cases of MST examined in this work. Further analysis on the effective spatial dimensionality reveal that MST remains at d = 3 under proton irradiation transitioning from an n = 1 spin dimensionality to n = 2 and n=3 for 1 x 10^15 and 5 x 10^15 H+/cm^2, indicating an XY interaction and a Heisenberg interaction, respectively. The pair (spin-spin) correlation function reveals an increase in magnetic correlations at the proton irradiance of 5 x 10^15 H+/cm^2. In conjunction, the maximum change in magnetic entropy obtained from isothermal magnetization at 3 T is the largest for 5 x 10^15 H+/cm^2 with a value of 2.45 J/kgK at T = 73.66 K, in comparison to 1.60 J/kgK for pristine MST at T = 73 K. Magnetic entropy derived from zero-field heat capacity does not show large deviations across the proton irradiated samples. This suggests that the antiferromagnetic coupling between the Mn sites is stable even after proton irradiation. Such result implies that magnetization is enhanced through a strengthening of the super-exchange interaction between Mn atoms mediated through Te rather than a weakening of the AFM component. Overall, our study finds that the magnetic interactions are manipulated the greatest when MST is irradiated at 5 x 10^15 H+/cm^2.

cond-mat.mtrl-sci↗

arXiv2021

Realizing topologically ordered states on a quantum processor

The discovery of topological order has revolutionized the understanding of quantum matter in modern physics and provided the theoretical foundation for many quantum error correcting codes. Realizing topologically ordered states has proven to be extremely challenging in both condensed matter and synthetic quantum systems. Here, we prepare the ground state of the toric code Hamiltonian using an efficient quantum circuit on a superconducting quantum processor. We measure a topological entanglement entropy near the expected value of $\ln2$, and simulate anyon interferometry to extract the braiding statistics of the emergent excitations. Furthermore, we investigate key aspects of the surface code, including logical state injection and the decay of the non-local order parameter. Our results demonstrate the potential for quantum processors to provide key insights into topological quantum matter and quantum error correction.

quant-ph↗

arXiv2021

Probing charge density wave phases and the Mott transition in $1T$-TaS$_2$ by inelastic light scattering

We present a polarization-resolved, high-resolution Raman scattering study of the three consecutive charge density wave (CDW) regimes in $1T$-TaS$_2$ single crystals, supported by \textit{ab initio} calculations. Our analysis of the spectra within the low-temperature commensurate (C-CDW) regime shows $\mathrm{P3}$ symmetry of the system, thus excluding the previously proposed triclinic stacking of the "star-of-David" structure, and promoting trigonal or hexagonal stacking instead. The spectra of the high-temperature incommensurate (IC-CDW) phase directly project the phonon density of states due to the breaking of the translational invariance, supplemented by sizeable electron-phonon coupling. Between 200 and 352\,K, our Raman spectra show contributions from both the IC-CDW and the C-CDW phase, indicating their coexistence in the so-called nearly-commensurate (NC-CDW) phase. The temperature-dependence of the symmetry-resolved Raman conductivity indicates the stepwise reduction of the density of states in the CDW phases, followed by a Mott transition within the C-CDW phase. We determine the size of the Mott gap to be $Ω_{\rm gap}\approx 170-190$ meV, and track its temperature dependence.

cond-mat.str-el↗

arXiv2021

Property investigation for different wedge-shaped CsI(Tl)s

Two types of wedge-shaped CsI(Tl)s were designed to be placed behind the annular double-sided silicon detectors (ADSSDs) to identify the light charged particles with the $ΔE-E$ method. The properties of CsI(Tl)s with different shapes and sizes, such as energy resolution, light output non-uniformity and particle identification capability, were compared by using a $α$-source and a radioactive beam of $^{15}$C. The big-size CsI(Tl) was finally adopted to form the $ΔE-E$ telescope due to better properties. The property differences of these two types of CsI(Tl)s can be interpreted based on the Geant4 simulation results.

physics.ins-det↗

arXiv2021

Study of $s$- and $d$-wave intruder strengths in $^{13}{\rm B}_{\rm g.s.}$ via a $p(^{13}{\rm B},d)^{12}{\rm B}$ reaction

Experimental results of the $p(^{13}{\rm B},d)^{12}{\rm B}$ transfer reaction to the low-lying states in $^{12}$B are reported. The optical potential parameters for the entrance channel are extracted from the elastic scattering $p$($^{13}{\rm B}$, $p$) measured in the same experiment, while those for the exit channel are global ones. Spectroscopic factors associated with the $p$-, $s$-, and $d$-wave neutron transfer to the known $^{12}$B states, are extracted by comparing the deuteron angular distributions with the calculation results. The separated $s$- and $d$-wave intruder strengths in $^{13}{\rm B}_{\rm g.s.}$ were determined to be $10(2)\%$ and $6(1)\%$, respectively, which follow roughly the systematics for the $N$ = 8 neutron-rich isotones. The measured total intruder strength is in good agreement with the shell model calculation, while the individual ones evolve quite differently. Particularly, the sudden change of the $d$-wave intensity between $^{13}$B and $^{12}$Be needs further theoretical interpretation.

nucl-ex↗

arXiv2021

Computational study of simultaneous positive and negative streamer propagation in a twin surface dielectric barrier discharge via 2D PIC simulations

The propagation mechanisms of plasma streamers have been observed and investigated in a surface dielectric barrier discharge (SDBD) using 2D particle in cell simulations. The investigations are carried out under a simulated air mixture, 80\% N$_2$ and 20\% O$_2$, at atmospheric pressure, 100$\,$kPa, under both DC conditions and a pulsed DC waveform that represent AC conditions. The simulated geometry is a simplification of the symmetric and fully exposed SDBD resulting in the simultaneous ignition of both positive and negative streamers on either side of the Al$_2$O$_3$ dielectric barrier. In order to determine the interactivity of the two streamers, the propagation behavior for the positive and negative streamers are investigated both independently and simultaneously under identical constant voltage conditions. An additional focus is implored under a fast sub nanosecond rise time square voltage pulse alternating between positive and negative voltage conditions, thus providing insight into the dynamics of the streamers under alternating polarity switches. It is shown that the simultaneous ignition of both streamers, as well as using the pulsed DC conditions, provides both an enhanced discharge and an increased surface coverage. It is also shown that additional streamer branching may occur in a cross section that is difficult to experimentally observe. The enhanced discharge and surface coverage may be beneficial to many applications such as, but are not limited to: air purification, volatile organic compound removal, and plasma enhanced catalysis.

physics.plasm-ph↗

arXiv2020

Characterization of cubic Li$_{2}$$^{100}$MoO$_4$ crystals for the CUPID experiment

The CUPID Collaboration is designing a tonne-scale, background-free detector to search for double beta decay with sufficient sensitivity to fully explore the parameter space corresponding to the inverted neutrino mass hierarchy scenario. One of the CUPID demonstrators, CUPID-Mo, has proved the potential of enriched Li$_{2}$$^{100}$MoO$_4$ crystals as suitable detectors for neutrinoless double beta decay search. In this work, we characterised cubic crystals that, compared to the cylindrical crystals used by CUPID-Mo, are more appealing for the construction of tightly packed arrays. We measured an average energy resolution of (6.7$\pm$0.6) keV FWHM in the region of interest, approaching the CUPID target of 5 keV FWHM. We assessed the identification of $α$ particles with and without a reflecting foil that enhances the scintillation light collection efficiency, proving that the baseline design of CUPID already ensures a complete suppression of this $α$-induced background contribution. We also used the collected data to validate a Monte Carlo simulation modelling the light collection efficiency, which will enable further optimisations of the detector.

physics.ins-det↗

arXiv2020

A CUPID Li$_{2}$$^{100}$MoO$_4$ scintillating bolometer tested in the CROSS underground facility

A scintillating bolometer based on a large cubic Li$_{2}$$^{100}$MoO$_4$ crystal (45 mm side) and a Ge wafer (scintillation detector) has been operated in the CROSS cryogenic facility at the Canfranc underground laboratory in Spain. The dual-readout detector is a prototype of the technology that will be used in the next-generation $0\nu2β$ experiment CUPID. The measurements were performed at 18 and 12 mK temperature in a pulse tube dilution refrigerator. This setup utilizes the same technology as the CUORE cryostat that will host CUPID and so represents an accurate estimation of the expected performance. The Li$_{2}$$^{100}$MoO$_4$ bolometer shows a high energy resolution of 6 keV FWHM at the 2615 keV $γ$ line. The detection of scintillation light for each event triggered by the Li$_{2}$$^{100}$MoO$_4$ bolometer allowed for a full separation ($\sim$8$σ$) between $γ$($β$) and $α$ events above 2 MeV. The Li$_{2}$$^{100}$MoO$_4$ crystal also shows a high internal radiopurity with $^{228}$Th and $^{226}$Ra activities of less than 3 and 8 $μ$Bq/kg, respectively. Taking also into account the advantage of a more compact and massive detector array, which can be made of cubic-shaped crystals (compared to the cylindrical ones), this test demonstrates the great potential of cubic Li$_{2}$$^{100}$MoO$_4$ scintillating bolometers for high-sensitivity searches for the $^{100}$Mo $0\nu2β$ decay in CROSS and CUPID projects.

physics.ins-det↗

arXiv2020

Quantum critical dynamics in a spinor Hubbard model quantum simulator

Three-dimensional (3D) strongly correlated many-body systems, especially their dynamics across quantum phase transitions, are prohibitively difficult to be numerically simulated. We experimentally demonstrate that such complex many-body dynamics can be efficiently studied in a 3D spinor Bose-Hubbard model quantum simulator, consisting of antiferromagnetic spinor Bose-Einstein condensates confined in cubic optical lattices. We find novel dynamics and scaling effects beyond the scope of existing theories at superfluid-insulator quantum phase transitions and highlight spin populations as a new observable to probe the quantum critical dynamics. Our data indicate that the scaling exponents are independent of the nature of the quantum phase transitions. We also conduct numerical simulations in lower dimensions using time-dependent Gutzwiller approximations, which qualitatively describe our observations.

cond-mat.quant-gas↗

arXiv2020

A new CMY camera technology using Al-TiO2-Al nanorod filter mosaic integrated on a CMOS image sensor

A CMY colour camera differs from its RGB counterpart in that it employs a subtractive colour space of cyan, magenta and yellow. CMY cameras tend to performs better than RGB cameras in low light conditions due to their much higher transmittance. However, conventional CMY colour filter technology made of pigments and dyes are limited in performance for the next generation image sensors with submicron pixel sizes. These conventional filters are difficult to fabricate at nanoscale dimensions as they use their absorption properties to subtract colours. This paper presents a CMOS compatible nanoscale thick CMY colour mosaic made of Al-TiO2-Al nanorods forming an array 0.82 million colour pixels of 4.4 micron each, arranged in a CMYM pattern. The colour mosaic was then integrated onto a MT9P031 monochrome image sensor to make a CMY camera and the colour imaging demonstrated using a 12 colour Macbeth chart. The developed technology will have applications in astronomy, low exposure time imaging in biology and photography.

physics.ins-det↗

arXiv2020

An Algorithm to locate the centers of Baryon Acoustic Oscillations

The cosmic structure formed from Baryon Acoustic Oscillations (BAO) in the early universe is imprinted in the galaxy distribution observable in large scale surveys, and is used as a standard ruler in contemporary cosmology. BAO are typically detected as a preferential length scale in two point statistics, which gives little information about the location of BAO structures in real space. The aim of the algorithm described in this paper is to find probable centers of BAO in the cosmic matter distribution. The algorithm convolves the three dimensional distribution of matter density with a spherical shell kernel of variable radius placed at different locations. The locations that correspond to the highest values of the convolution correspond to the probable centers of BAO. This method is realized in an open-source, computationally efficient algorithm. We describe the algorithm and present the results of applying it to the SDSS DR9 CMASS survey and associated mock catalogs. A detailed performance study demonstrates the algorithm's ability to locate BAO centers, and in doing so presents a novel detection of the BAO scale in galaxy surveys.

astro-ph.CO↗

arXiv2020

Magnetism of Nd$_2$O$_3$ single crystals near the Néel temperature

Single crystals of Nd$_2$O$_3$ were grown and characterized using neutron scattering and thermodynamic measurements. Nd$_2$O$_3$ has long-range antiferromagnetic order below $T_{\rm N}$ = 0.55 K and specific heat measurements have demonstrated that a significant amount of the magnetic entropy is released above $T_{\rm N}$. Inelastic neutron scattering experiments reveal a magnetic mode(s) with little dispersion peaked at $\approx$ 0.37 meV that is of greatest intensity below $T_{\rm N}$ but persists above 2$T_{\rm N}$. This persistence of dynamic correlations is likely related to frustrated interactions associated with the nearly-ideal stacked triangular lattice geometry of $J_{\textrm{eff}}$ = 1/2 spins on Nd$^{3+}$ ions. The magnetization is observed to be strongly anisotropic at all temperatures due to crystal field effects, with easy-plane anisotropy observed. A non-compensated magnetic structure is inferred from the temperature-dependence of the magnetization when a magnetic field of sufficient strength is applied within the basal plane near $T_{\rm N}$, and the evolution of the long-range order is summarized in a temperature-field phase diagram.

cond-mat.str-el↗

arXiv2020

The Integrated Pulse Profiles of Fast Radio Bursts

Multi-peaked features appear on the integrated pulse profiles of fast radio burst observed below 2.5 GHz and the instantaneous spectrum of many bursts observed between 4 and 8 GHz. The mechanism of pulse or spectrum shaping has attracted little attention. Here we show that these interference-like pulse profiles are mostly the instantaneous spectra near the source regions of fast radio bursts. The corresponding instantaneous spectra are coincident to the spectrum from a single electron passing through a tapered undulator. The multi-peaked spectrum observed between 4 and 8 GHz can also be explained consistently by this type of spectrum. The spectrum is invisible unless the particles in the radiation beam are bunched. The bunching effect is probably due to the acceleration of particles in the plasma wakefield.

astro-ph.HE↗

arXiv2020

Resonance Laser Ionization Spectroscopy of Selenium

Photoionization spectra of Se have been studied by step-wise resonance laser ionization. The Rydberg series 4s$^2$4p$^3$($^4$S)np $^3$P$_{0,1,2}$ and 4s$^2$4p$^3$($^4$S)np $^5$P$_{1,2,3}$ were measured via different excitation schemes. Using the Rydberg series 4s$^2$4p$^3$($^4$S)np $^3$P$_2$ with n=15-33, the ionization potential of Se was determined with improved precision to 76658.15(2)$_{stat}$(4)$_{sys}$ cm$^{-1}$, which resolved the discrepancy in previous literatures. Autoionizing (AI) spectra between the IP and two neighboring converging limits of the Se ionic states 4s$^2$4p$^3$($^2$D$_{3/2}$) and 4s$^2$4p$^3$($^2$D$_{5/2}$) were obtained. In total eight AI Rydberg series have been observed, measured and assigned.

physics.atom-ph↗