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Y. Deng

Publications and source records attributed to Y. Deng.

At least 37 records · Page 2Linked to original sources
arXiv2021

Quenching factor measurements of neon nuclei in neon gas

The NEWS-G collaboration uses Spherical Proportional Counters (SPCs) to search for weakly interacting massive particles (WIMPs). In this paper, we report the first measurements of the nuclear quenching factor in neon gas at \SI{2}{bar} using an SPC deployed in a neutron beam at the TUNL facility. The energy-dependence of the nuclear quenching factor is modelled using a simple power law: $α$E$_{nr}^β$; we determine its parameters by simultaneously fitting the data collected with the detector over a range of energies. We measured the following parameters in Ne:CH$_{4}$ at \SI{2}{bar}: $α$ = 0.2801 $\pm$ 0.0050 (fit) $\pm$ 0.0045 (sys) and $β$ = 0.0867 $\pm$ 0.020 (fit) $\pm$ 0.006(sys). Our measurements do not agree with expected values from SRIM or Lindhard theory. We demonstrated the feasibility of performing quenching factor measurements at sub-keV energies in gases using SPCs and a neutron beam.

physics.ins-det↗
arXiv2021

Heat capacity of URu$_{2-x}$Os$_x$Si$_2$ at low temperatures

We perform measurements of the heat capacity as a function of temperature in URu$_{2-x}$Os$_x$Si$_2$ alloys. Our experimental results show that the critical temperature of the second-order phase transition increases while the value of the Sommerfeld coefficient in the ordered state decreases with an increase in osmium concentration. We also observe the increase in the values of the heat capacity at the critical temperature as well as a broadening of the critical fluctuations region with an increase in $x$. We analyze the experimental data using the Haule-Kotliar model which, in particular, identifies the 'hidden order' transition in the parent material URu$_2$Si$_2$ as a transition to a state with nonzero hexadecapole moment. We demonstrate that our experimental results are consistent with the predictions of that model.

cond-mat.str-el↗
arXiv2021

Excited-state band structure mapping

Angle-resolved photoelectron spectroscopy is an extremely powerful probe of materials to access the occupied electronic structure with energy and momentum resolution. However, it remains blind to those dynamic states above the Fermi level that determine technologically relevant transport properties. In this work, we extend band structure mapping into the unoccupied states and across the entire Brillouin zone by using a state-of-the-art high repetition rate, extreme ultraviolet fem- tosecond light source to probe optically excited samples. The wide-ranging applicability and power of this approach are demonstrated by measurements on the 2D semiconductor WSe2, where the energy-momentum dispersion of valence and conduction bands are observed in a single experiment. This provides a direct momentum-resolved view not only on the complete out-of-equilibrium band gap but also on its renormalization induced by electron-hole interaction and screening. Our work establishes a new benchmark for measuring the band structure of materials, with direct access to the energy-momentum dispersion of the excited-state spectral function.

cond-mat.mtrl-sci↗
arXiv2020

Copper electroplating for background suppression in the NEWS-G experiment

New Experiments with Spheres-Gas (NEWS-G) is a dark matter direct detection experiment that will operate at SNOLAB (Canada). Similar to other rare-event searches, the materials used in the detector construction are subject to stringent radiopurity requirements. The detector features a 140-cm diameter proportional counter comprising two hemispheres made from commercially sourced 99.99% pure copper. Such copper is widely used in rare-event searches because it is readily available, there are no long-lived Cu radioisotopes, and levels of non-Cu radiocontaminants are generally low. However, measurements performed with a dedicated 210Po alpha counting method using an XIA detector confirmed a problematic concentration of 210Pb in bulk of the copper. To shield the proportional counter's active volume, a low-background electroforming method was adapted to the hemispherical shape to grow a 500-$μ$m thick layer of ultra-radiopure copper to the detector's inner surface. In this paper the process is described, which was prototyped at Pacific Northwest National Laboratory (PNNL), USA, and then conducted at full scale in the Laboratoire Souterrain de Modane in France. The radiopurity of the electroplated copper was assessed through Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Measurements of samples from the first (second) hemisphere give 68% confidence upper limits of <0.58 $μ$Bq/kg (<0.24 $μ$Bq/kg) and <0.26 $μ$Bq/kg (<0.11 $μ$Bq/kg) on the 232Th and 238U contamination levels, respectively. These results are comparable to previously reported measurements of electroformed copper produced for other rare-event searches, which were also found to have low concentration of 210Pb consistent with the background goals of the NEWS-G experiment.

physics.ins-det↗
arXiv2019

Time- and angle-resolved photoemission spectroscopy of solids in the extreme ultraviolet at 500 kHz repetition rate

Time- and angle-resolved photoelectron spectroscopy (trARPES) employing a 500 kHz extreme-ultravioled (XUV) light source operating at 21.7 eV probe photon energy is reported. Based on a high-power ytterbium laser, optical parametric chirped pulse amplification (OPCPA), and ultraviolet-driven high-harmonic generation, the light source produces an isolated high-harmonic with 110 meV bandwidth and a flux of more than $10^{11}$ photons/second on the sample. Combined with a state-of-the-art ARPES chamber, this table-top experiment allows high-repetition rate pump-probe experiments of electron dynamics in occupied and normally unoccupied (excited) states in the entire Brillouin zone and with a temporal system response function below 40 fs.

physics.ins-det↗
arXiv2019

Enhanced magnetic ordering in Sm metal under extreme pressure

The dependence of the magnetic ordering temperature To of Sm metal was determined through four-point electrical resistivity measurements to pressures as high as 150 GPa. A strong increase in To with pressure is observed above 85 GPa. In this pressure range Sm ions alloyed in dilute concentration with superconducting Y exhibit giant Kondo pair breaking. Taken together, these results suggest that for pressures above 85 GPa Sm is in a highly correlated electron state, like a Kondo lattice, with an unusually high value of To. A detailed comparison is made with similar results obtained earlier on Nd, Tb and Dy and their dilute magnetic alloys with superconducting Y.

cond-mat.str-el↗
arXiv2018

Global solutions of the gravity-capillary water-wave system in three dimensions

In this paper we prove global regularity for the full water waves system in 3 dimensions for small data, under the influence of both gravity and surface tension. This problem presents essential difficulties which were absent in all of the earlier global regularity results for other water wave models. To construct global solutions we use a combination of energy estimates and matching dispersive estimates. There is a significant new difficulty in proving energy estimates in our problem, namely the combination of slow pointwise decay of solutions (no better than $|t|^{-5/6}$) and the presence of a large, codimension 1, set of quadratic time-resonances. To deal with such a situation we propose here a new mechanism, which exploits a non-degeneracy property of the time-resonant hypersurfaces and some special structure of the quadratic part of the nonlinearity, connected to the conserved energy of the system. The dispersive estimates rely on analysis of the Duhamel formula in the Fourier space. The main contributions come from the set of space-time resonances, which is a large set of dimension 1. To control the corresponding bilinear interactions we use Harmonic Analysis techniques, such as orthogonality arguments in the Fourier space and atomic decompositions of functions. Most importantly, we construct and use a refined norm which is well adapted to the geometry of the problem.

math.AP↗
arXiv2018

Spin-orbit-coupled Bose-Einstein condensates of rotating polar molecules

An experimental proposal for realizing spin-orbit (SO) coupling of pseudospin-1 in the ground manifold $^1Σ(\upsilon=0)$ of (bosonic) bialkali polar molecules is presented. The three spin components are composed of the ground rotational state and two substates from the first excited rotational level. Using hyperfine resolved Raman processes through two select excited states resonantly coupled by a microwave, an effective coupling between the spin tensor and linear momentum is realized. The properties of Bose-Einstein condensates for such SO-coupled molecules exhibiting dipolar interactions are further explored. In addition to the SO-coupling-induced stripe structures, the singly and doubly quantized vortex phases are found to appear, implicating exciting opportunities for exploring novel quantum physics using SO-coupled rotating polar molecules with dipolar interactions.

cond-mat.quant-gas↗
arXiv2017

Tunable topological phases with fermionic atoms in a one-dimensional flux lattice

We present a simple scheme for implementing a one-dimensional (1D) magnetic-flux lattice of ultracold fermionic spin-$1/2$ atoms. The resulting tight-binding model supports gapped and gapless topological phases, and chiral currents for Meissner and vortex phases. Its single-particle spectra exhibit topological flat bands at small flux, and the flatness sensitively depends on hopping strength. An effective $p$-wave interaction arises in a $s$-wave paired superfluid. Treating atomic internal states as forming a synthetic dimension and balancing the interplay of magnetic flux and Zeeman field, our model describes a tunable topological Fermi superfluid, which paves the way towards experimental explorations of non-Abelian topological matter in 1D atomic quantum gases.

cond-mat.quant-gas↗
arXiv2017

Pressure-tuning of bond-directional exchange interactions and magnetic frustration in hyperhoneycomb iridate $β$-$\mathrm{Li_2IrO_3}$

We explore the response of Ir $5d$ orbitals to pressure in $β$-$\mathrm{Li_2IrO_3}$, a hyperhoneycomb iridate in proximity to a Kitaev quantum spin liquid (QSL) ground state. X-ray absorption spectroscopy reveals a reconstruction of the electronic ground state below 2 GPa, the same pressure range where x-ray magnetic circular dichroism shows an apparent collapse of magnetic order. The electronic reconstruction, which manifests a reduction in the effective spin-orbit (SO) interaction in $5d$ orbitals, pushes $β$-$\mathrm{Li_2IrO_3}$ further away from the pure $J_{\rm eff}=1/2$ limit. Although lattice symmetry is preserved across the electronic transition, x-ray diffraction shows a highly anisotropic compression of the hyperhoneycomb lattice which affects the balance of bond-directional Ir-Ir exchange interactions driven by spin-orbit coupling at Ir sites. An enhancement of symmetric anisotropic exchange over Kitaev and Heisenberg exchange interactions seen in theoretical calculations that use precisely this anisotropic Ir-Ir bond compression provides one possible route to realization of a QSL state in this hyperhoneycomb iridate at high pressures.

cond-mat.str-el↗
arXiv2017

Exotic Topological States with Raman-Induced Spin-Orbit Coupling

We propose a simple experimental scheme to realize simultaneously the one-dimensional spin-orbit coupling and the staggered spin-flip in ultracold pseudospin-$1/2$ atomic Fermi gases trapped in square optical lattices. In the absence of interspecies interactions, the system supports gapped Chern insulators and gapless topological semimetal states. By turning on the $s$-wave interactions, a rich variety of gapped and gapless inhomogeneous topological superfluids can emerge. In particular, a gapped topological Fulde-Ferrell superfluid, in which the chiral edge states at opposite boundaries possess the same chirality, is predicted.

cond-mat.quant-gas↗
arXiv2016

Unbounded Norm Convergence in Banach Lattices

A net $(x_α)$ in a vector lattice $X$ is unbounded order convergent to $x \in X$ if $\lvert x_α- x\rvert \wedge u$ converges to $0$ in order for all $u\in X_+$. This convergence has been investigated and applied in several recent papers by Gao et al. It may be viewed as a generalization of almost everywhere convergence to general vector lattices. In this paper, we study a variation of this convergence for Banach lattices. A net $(x_α)$ in a Banach lattice $X$ is unbounded norm convergent to $x$ if $\lVert\lvert x_α- x\rvert \wedge u\rVert\to 0$ for all $u\in X_+$. We show that this convergence may be viewed as a generalization of convergence in measure. We also investigate its relationship with other convergences.

math.FA↗
arXiv2014

Spinor Bose-Einstein Condensates of Rotating Polar Molecules

We propose a scheme to realize a pseudospin-$1/2$ model of the $^{1}Σ(v=0)$ bialkali polar molecules with the spin states corresponding to two sublevels of the first excited rotational level. We show that the effective dipole-dipole interaction between two spin-$1/2$ molecules couples the rotational and orbital angular momenta and is highly tunable via a microwave field. We also investigate the ground state properties of a spin-$1/2$ molecular condensate. A variety of nontrivial quantum phases, including the doubly-quantized vortex states, are discovered. Our scheme can also be used to create spin-$1$ model of polar molecules. Thus, we show that the ultracold gases of bialkali polar molecules provide a unique platform for studying the spinor condensates of rotating molecules.

cond-mat.quant-gas↗
arXiv2014

The time series forecasting: from the aspect of network

Forecasting can estimate the statement of events according to the historical data and it is considerably important in many disciplines. At present, time series models have been utilized to solve forecasting problems in various domains. In general, researchers use curve fitting and parameter estimation methods (moment estimation, maximum likelihood estimation and least square method) to forecast. In this paper, a new sight is given to the forecasting and a completely different method is proposed to forecast time series. Inspired by the visibility graph and link prediction, this letter converts time series into network and then finds the nodes which are mostly likelihood to link with the predicted node. Finally, the predicted value will be obtained according to the state of the link. The TAIEX data set is used in the case study to illustrate that the proposed method is effectiveness. Compared with ARIMA model, the proposed shows a good forecasting performance when there is a small amount of data.

physics.data-an↗
arXiv2013

Bose-Einstein Condensates with Cavity-Mediated Spin-Orbit Coupling

We propose a novel scheme to generate the spin-orbit coupling for a condensate placed inside an optical cavity by using a standing wave and a traveling wave. It is shown that the interplay of the laser lights and the cavity gives rise to rich quantum phases. Our scheme also generates an nontrivial lattice of the magnetic flux, which may facilitate the study of the exotic quantum phases.

cond-mat.quant-gas↗
arXiv2012

Spin-orbit-coupled dipolar Bose-Einstein condensates

We propose an experimental scheme to create spin-orbit coupling in spin-3 Cr atoms using Raman processes. Employing linear Zeeman effect and optical Stark shift, two spin states within the ground electronic manifold are selected, which results in a pseudo-spin-1/2 model. We further study the ground state structures of a spin-orbit-coupled Cr condensate. We show that, in addition to the stripe structures induced by the spin-orbit coupling, the magnetic dipole-dipole interaction gives rise to the vortex phase, in which spontaneous spin vortex is formed.

cond-mat.quant-gas↗