Searching for a preferred direction with Union2.1 data

A cosmological preferred direction was reported from the type Ia supernovae (SNe Ia) data in recent years. We use the Union2.1 data to give a simple classification of such studies for the first time. Because the maximum anisotropic direction is independent of isotropic dark energy models, we adopt two cosmological models ($\Lambda$CDM, $w$CDM) for the hemisphere comparison analysis and $\Lambda$CDM model for dipole fit approach. In hemisphere comparison method, the matter density and the equation of state of dark energy are adopted as the diagnostic qualities in the $\Lambda$CDM model and $w$CDM model, respectively. In dipole fit approach, we fit the fluctuation of distance modulus. We find that there is a null signal for the hemisphere comparison method, while a preferred direction ($b=-14.3^\circ \pm 10.1^\circ, l=307.1^\circ \pm 16.2^\circ$) for the dipole fit method. This result indicates that the dipole fit is more sensitive than the hemisphere comparison method.Comment: 8 pages, 2 figures, accepted for publication in MNRA

Electronic and phonon excitations in {\alpha}-RuCl3_3

We report on THz, infrared reflectivity and transmission experiments for wave numbers from 10 to 8000 cm$^{-1}$ ($\sim$ 1 meV - 1 eV) and for temperatures from 5 to 295 K on the Kitaev candidate material {\alpha}-RuCl$_3$. As reported earlier, the compound under investigation passes through a first-order structural phase transition, from a monoclinic high-temperature to a rhombohedral low-temperature phase. The phase transition shows an extreme and unusual hysteretic behavior, which extends from 60 to 166 K. In passing this phase transition, in the complete frequency range investigated we found a significant reflectance change, which amounts almost a factor of two. We provide a broadband spectrum of dielectric constant, dielectric loss and optical conductivity from the THz to the mid infrared regime and study in detail the phonon response and the low-lying electronic density of states. We provide evidence for the onset of an optical energy gap, which is of order 200 meV, in good agreement with the gap derived from measurements of the DC electrical resistivity. Remarkably, the onset of the gap exhibits a strong blue shift on increasing temperatures.Comment: 18 pages, 7 figure

THz spectroscopy in the pseudo-Kagome system Cu3Bi(SeO3)2O2Br

Terahertz (THz) transmission spectra have been measured as function of temperature and magnetic field on single crystals of Cu3Bi(SeO3)2O2Br. In the time-domain THz spectra without magnetic field, two resonance absorptions are observed below the magnetic ordering temperature T_N~27.4 K. The corresponding resonance frequencies increase with decreasing temperature and reach energies of 1.28 and 1.23 meV at 3.5 K. Multi-frequency electron spin resonance transmission spectra as a function of applied magnetic field show the field dependence of four magnetic resonance modes, which can be modeled as a ferromagnetic resonance including demagnetization and anisotropy effects.Comment: 5 pages, 3 figures. All comments are welcome and appreciate

QCD Matter Thermalization at RHIC and LHC

Employing the perturbative QCD inspired parton cascade, we investigate kinetic and chemical equilibration of the partonic matter created in central heavy ion collisions at RHIC and LHC energies. Two types of initial conditions are chosen. One is generated by the model of wounded nucleons using the PYTHIA event generator and Glauber geometry. Another is considered as a color glass condensate. We show that kinetic equilibration is almost independent on the chosen initial conditions, whereas there is a sensitive dependence for chemical equilibration. The time scale of thermalization lies between 1 and 1.5 fm/c. The final parton transverse energy obtained from BAMPS calculations is compared with the RHIC data and is estimated for the LHC energy.Comment: 8 pages, 10 figures, plenary talk at International Conference on Strangeness in Quark Matter 2008, Beijing, China, October 6-10, 200

Symmetry-dependent screening of surface plasmons in ultrathin supported films: The case of Al/Si(111)

A joint theoretical and experimental study of plasmon excitations for Al overlayers on Si(111) has been carried out. The presence of the substrate is found to drastically modify the hybridization and charge density response of the surface plasmons of the metal overlayers. The symmetric mode, which is polarized toward the Al/Si interface, is strongly damped in intensity and significantly redshifted in energy. However, the antisymmetric mode, which is polarized to the metal-vacuum interface, is essentially unaffected by the presence of the substrate. A low-energy acoustic plasmon mode is also found in a one monolayer Al film and is almost unaffected by the substrate. The calculated plasmon dispersions with substrate are in good agreement with experimental data measured by electron energy loss spectroscopy. Our results suggest that interaction and screening at the subnanometer scale are symmetry dependent, a conclusion that may have general implications in other thin films and related structures

An all fiber source of frequency entangled photon pairs

We present an all fiber source of frequency entangled photon pairs by using four wave mixing in a Sagnac fiber loop. Special care is taken to suppress the impurity of the frequency entanglement by cooling the fiber and by matching the polarization modes of the photon pairs counter-propagating in the fiber loop. Coincidence detection of signal and idler photons, which are created in pair and in different spatial modes of the fiber loop, shows the quantum interference in the form of spatial beating, while the single counts of the individual signal (idler) photons keep constant. When the production rate of photon pairs is about 0.013 pairs/pulse, the envelope of the quantum interference reveals a visibility of $(95\pm 2)$, which is close to the calculated theoretical limit 97.4%Comment: 11 pages, 6 figures, to appear in Phys. Rev.

Magnetic Excitations and Continuum of a Field-Induced Quantum Spin Liquid in α\alpha-RuCl3_3

We report on terahertz spectroscopy of quantum spin dynamics in $\alpha$-RuCl$_3$, a system proximate to the Kitaev honeycomb model, as a function of temperature and magnetic field. An extended magnetic continuum develops below the structural phase transition at $T_{s2}=62$K. With the onset of a long-range magnetic order at $T_N=6.5$K, spectral weight is transferred to a well-defined magnetic excitation at $\hbar \omega_1 = 2.48$meV, which is accompanied by a higher-energy band at $\hbar \omega_2 = 6.48$meV. Both excitations soften in magnetic field, signaling a quantum phase transition at $B_c=7$T where we find a broad continuum dominating the dynamical response. Above $B_c$, the long-range order is suppressed, and on top of the continuum, various emergent magnetic excitations evolve. These excitations follow clear selection rules and exhibit distinct field dependencies, characterizing the dynamical properties of the field-induced quantum spin liquid