arXiv subjects

Wei Guo

Publications and source records attributed to Wei Guo.

335 records · Page 19Linked to original sources

arXiv2013

A Concept for A Dark Matter Detector Using Liquid Helium-4

Direct searches for light dark matter particles (mass $<10$ GeV) are especially challenging because of the low energies transferred in elastic scattering to typical heavy nuclear targets. We investigate the possibility of using liquid Helium-4 as a target material, taking advantage of the favorable kinematic matching of the Helium nucleus to light dark matter particles. Monte Carlo simulations are performed to calculate the charge, scintillation, and triplet helium molecule signals produced by recoil He ions, for a variety of energies and electric fields. We show that excellent background rejection can be achieved based on the ratios between different signal channels. We also present some concepts for a liquid-helium-based dark matter detector. Key to the proposed approach is the use of a large electric field to extract electrons from the event site, and the amplification of this charge signal, through proportional scintillation, liquid electroluminescence, or roton emission. The sensitivity of the proposed detector to light dark matter particles is estimated for various electric fields and light collection efficiencies.

astro-ph.IM↗

arXiv2012

Polariton Bose-Einstein condensate at room temperature in a Al(Ga)N nanowire-dielectric microcavity with a spatial potential trap

A spatial potential trap is formed in a 6.0 μm Al(Ga)N nanowire by varying the Al composition along its length during epitaxial growth. The polariton emission characteristics of a dielectric microcavity with the single nanowire embedded in-plane has been studied at room temperature. Excitation is provided at the Al(Ga)N end of the nanowire and polariton emission is observed from the lowest bandgap GaN region of the nanowire. Comparison of the results with those measured in an identical microcavity with an uniform GaN nanowire and having an identical exciton-photon detuning suggests evaporative cooling of the polaritons as they are transported across the trap in the Al(Ga)N nanowire. Measurement of the spectral characteristics of the polariton emission, their momentum distribution, first-order spatial coherence and time-resolved measurements of polariton cooling provide strong evidence of the formation of an equilibrium Bose-Einstein condensate, a unique state of matter in solid state systems, in the GaN region of the nanowire, at room temperature. An equilibrium condensate is not formed in the GaN nanowire dielectric microcavity without the spatial potential trap.

cond-mat.mes-hall↗

arXiv2012

Radiative friction on an excited atom moving in vacuum

It is known that, when an excited atom spontaneously emits one photon, two effects are produced. First, the atom's internal and external states are entangled with the states of the emitted photon. Second, the atom receives a momentum transfered from the photon. In this work, the dynamics of such an atom in vacuum is studied. Through a specific calculation, it is demonstrated that these effects cause the atom to experience, on average, a friction force opposite to its initial velocity. Properties of the force are also discussed.

quant-ph↗

arXiv2010

Thermodynamics of rotating Bose gases in a trap

Novel ground state properties of rotating Bose gases have been intensively studied in the context of neutral cold atoms. We investigate the rotating Bose gas in a trap from a thermodynamic perspective, taking the charged ideal Bose gas in magnetic field (which is equivalent to a neutral gas in a synthetic magnetic field) as an example. It is indicated that the Bose-Einstein condensation temperature is irrelevant to the magnetic field, conflicting with established intuition that the critical temperature decreases with the field increasing. The specific heat and Landau diamagnetization also exhibit intriguing behaviors. In contrast, we demonstrate that the condensation temperature for neutral Bose gases in a rotating frame drops to zero in the fast rotation limit, signaling a non-condensed quantum phase in the ground state.

cond-mat.quant-gas↗

arXiv2010

Vortex Nucleation Induced Phonon Radiation from a Moving Electron Bubble in Superfluid 4He

We construct an efficient zero-temperature semi-local density functional to dynamically simulate an electron bubble passing through superfluid 4He under various pressures and electric fields up to nanosecond timescale. Our simulated drift velocity can be quantitatively compared to experiments particularly when pressure approaches zero. We find that the high-speed bubble experiences remarkable expansion and deformation before vortex nucleation occurs. Accompanied by vortex-ring shedding, drastic surface vibration is generated leading to intense phonon radiation into the liquid. The amount of energy dissipated by these phonons is found to be greater than the amount carried away solely by the vortex rings. These results may enrich our understanding about the vortex nucleation induced energy dissipation in this fascinating system.

cond-mat.other↗

arXiv2010

The optical microscopy with virtual image breaks a record: 50-nm resolution imaging is demonstrated

We demonstrate a new 'microsphere nanoscope' that uses ordinary SiO2 microspheres as superlenses to create a virtual image of the object in near field. The magnified virtual image greatly overcomes the diffraction limit. We are able to resolve clearly 50-nm objects under a standard white light source in both transmission and reflection modes. The resolution achieved for white light opens a new opportunity to image viruses, DNA and molecules in real time.

physics.optics↗

arXiv2010

Visualization study of counterflow in superfluid helium-4 using metastable helium molecules

Heat is carried in superfluid He-4 by the motion of the normal fluid$^{1}$, a counterflowing superfluid component serving to eliminate any net mass flow. It has been known for many years that above a critical heat current the superfluid component in this counterflow becomes turbulent. This turbulence takes the form of a disorganized tangle of quantized vortex lines and is maintained by the relative motion of the two fluids$^{2-3}$. It has been suspected that the normal fluid may also become turbulent$^{4}$, but experimental verification is difficult without a technique for visualizing the flow. Here we report a series of visualization studies on the normal-fluid component in a thermal counterflow performed by imaging the motion of seeded metastable helium molecules using a laser-induced-fluorescence technique$^{5-8}$. We present evidence that the flow of the normal fluid is indeed turbulent, at least at relatively large velocities. Thermal counterflow in which both components are turbulent presents us with a new and theoretically challenging type of turbulent behaviour.

physics.flu-dyn↗

arXiv2008

Lepton Flavor Violating $τ^- \to μ^- V^0$ Decays in the Two Higgs Doublet Model III

In this paper, the lepton flavor violating $τ^- \to μ^- V^0(V^0=ρ^0,ϕ,ω)$ decays are studied in the framework of the two Higgs doublet model(2HDM) III. We present a computation of the the $γ-$, $Z$ penguin and box diagrams contributions, and make an analysis of their impacts. Our results show that, among the $γ-$ penguins, the penguins with neutral Higgs in the loop are very larger than those with charged Higgs in the loop. We find that the model parameter $λ_{τμ}$ is tightly constrained at the order of $O(10^{-3})$ and the branching ratios of these decays are available at the experiment measure. With the high luminosity, the B factories have considerable capability to find these LFV processes. On the other hand, these processes can also provide some valuable information to future research and furthermore present the reliable evidence to test the 2HDM III model.

hep-ph↗

arXiv2008

Stability of multi-electron bubbles in liquid helium

The stability of multi-electron bubbles in liquid helium is investigated theoretically. We find that multi-electron bubbles are unstable against fission whenever the pressure is positive. It is shown that for moving bubbles the Bernoulli effect can result in a range of pressures over which the bubbles are stable.

cond-mat.other↗

arXiv2003

The superconducting state in a single CuO2 layer:Experimental findings and scenario

The notable results shown by Bozovic et al. from measurements of synthesized one-unit-cell thick of La1.85Sr0.15CuO4,La2CuO4 HTS/AF/HTS tri-layer junctions query the predictions by prevalent models since there is no observable mixing of superconductivity and anti-ferromagnetism betwween the layers. In this article we make a brief survey of experimental results on the electronic structure of high-Tc cuprates and magnetic properties. Based on our analysis, we attribute superconductivity of a single CuO2 layer to spin pairing via local exchange interactions.

cond-mat.supr-con↗

arXiv2003

From charge transfer type insulator to superconductor

We propose a microscopic model Hamiltonian to account for impurity doping induced insulator-superconductor transition and the coexistence of antiferromagnetism and superconductivity in the high-Tc cuprates. The crossover from non Fermi liquid to Fermi liquid regime characterized by delocalization of delocalization of d electrons at Cu sites is discussed.

cond-mat.supr-con↗