arXiv subjects

T. Hong

Publications and source records attributed to T. Hong.

25 records · Page 2Linked to original sources

arXiv2012

The 2MASS Tully-Fisher Survey : Mapping the Mass in the Universe

The 2MASS Tully-Fisher Survey (2MTF) aims to measure Tully-Fisher (TF) distances for all bright inclined spirals in the 2MASS Redshift Survey (2MRS) using high quality HI widths and 2MASS photometry. Compared with previous peculiar velocity surveys, the 2MTF survey provides more accurate width measurements and more uniform sky coverage, combining observations with the Green Bank, Arecibo and Parkes telescopes. With this new redshift-independent distance database, we will significantly improve our understanding of the mass distribution in the local universe.

astro-ph.CO↗

arXiv2012

Magnetic properties of the S=1/2 quasi square lattice antiferromagnet CuF2(H2O)2(pyz) (pyz=pyrazine) investigated by neutron scattering

We have performed elastic and inelastic neutron experiments on single crystal samples of the coordination polymer compound CuF2(H2O)2(pyz) (pyz=pyrazine) to study the magnetic structure and excitations. The elastic neutron diffraction measurements indicate a collinear antiferromagnetic structure with moments oriented along the [0.7 0 1] real-space direction and an ordered moment of 0.60 +/- 0.03 muB/Cu. This value is significantly smaller than the single ion magnetic moment, reflecting the presence of strong quantum fluctuations. The spin wave dispersion from magnetic zone center to the zone boundary points (0.5 1.5 0) and (0.5 0 1.5) can be described by a two dimensional Heisenberg model with a nearest neighbor magnetic exchange constant J2d = 0.934 +/-0.0025 meV. The inter-layer interaction Jperp in this compound is less than 1.5% of J2d. The spin excitation energy at the (0.5 0.5 0.5) zone boundary point is reduced when compared to the (0.5 1 0.5) zone boundary point by ~10.3 +/- 1.4 %. This zone boundary dispersion is consistent with quantum Monte Carlo and series expansion calculations which include corrections for quantum fluctuations to linear spin wave theory.

cond-mat.str-el↗

arXiv2012

Magnetic dispersion and anisotropy in multiferroic BiFeO3

We have determined the full magnetic dispersion relations of multiferroic BiFeO3. In particular, two excitation gaps originating from magnetic anisotropies have been clearly observed. The direct observation of the gaps enables us to accurately determine the Dzyaloshinskii-Moriya (DM) interaction and the single ion anisotropy. The DM interaction supports a strong magneto-electric coupling in this compound.

cond-mat.mtrl-sci↗

arXiv2012

Disorder-Driven Loss of Phase Coherence in a Quasi-2D Cold Atom System

We study the order parameter of a quasi-2D gas of ultracold atoms trapped in an optical potential in the presence of controllable disorder. Our results show that disorder drives phase fluctuations without significantly affecting the amplitude of the quasi-condensate order parameter. This is evidence that disorder can drive phase fluctuations in 2D systems, relevant to the phase-fluctuation mechanism for the superconductor-to-insulator phase transition (SIT) in disordered 2D superconductors.

cond-mat.quant-gas↗

arXiv2012

The correlation function of galaxy clusters and detection of baryon acoustic oscillations

We calculate the correlation function of 13,904 galaxy clusters of z \leq 0.4 selected from the cluster catalog of Wen, Han & Liu. The correlation function can be fitted with a power-law model ξ(r)=(r/R_0)^γ on the scales of 10h^(-1)Mpc \leq r \leq 50h^(-1)Mpc, with a larger correlation length of R_0=18.84\pm0.27 h^(-1)Mpc for clusters with a richness of R \geq 15 and a smaller length of R_0=16.15 \pm 0.13 h^(-1)Mpc for clusters with a richness of R \geq 5. The power law index of γ=2.1 is found to be almost the same for all cluster subsamples. A pronounced baryon acoustic oscillations (BAO) peak is detected at r ~ 110 h^(-1)Mpc with a significance of ~ 1.9σ. By analyzing the correlation function in the range of 20 h^(-1)Mpc \leq r \leq 200 h^(-1)Mpc, we find the constraints on distance parameters are D_v(0.276)=1077\pm55(1σ) Mpc and h=0.73 \pm 0.039 (1σ), which are consistent with the WMAP 7-year cosmology. However, the BAO signal from the cluster sample is stronger than expected and leads to a rather low matter density Ω_m h^2=0.093\pm0.0077 (1σ), which deviates from the WMAP 7-year result by more than 3 σ. The correlation function of the GMBCG cluster sample is also calculated and our detection of the BAO feature is confirmed.

astro-ph.CO↗

arXiv2011

Crystals for neutron scattering studies of quantum magnetism

We review a strategy for targeted synthesis of large single crystal samples of prototype quantum magnets for inelastic neutron scattering experiments. Four case studies of organic copper halogenide S=1/2 systems are presented. They are meant to illustrate that exciting experimental results pertaining to forefront many-body quantum physics can be obtained on samples grown using very simple techniques, standard laboratory equipment, and almost no experience in in advanced crystal growth techniques.

cond-mat.str-el↗

arXiv2011

Effects of Mirror Aberrations on Laguerre-Gaussian Beams in Interferometric Gravitational-Wave Detectors

A fundamental limit to the sensitivity of optical interferometers is imposed by Brownian thermal fluctuations of the mirrors' surfaces. This thermal noise can be reduced by using larger beams which "average out" the random fluctuations of the surfaces. It has been proposed previously that wider, higher-order Laguerre-Gaussian modes can be used to exploit this effect. In this article, we show that susceptibility to spatial imperfections of the mirrors' surfaces limits the effectiveness of this approach in interferometers used for gravitational-wave detection. Possible methods of reducing this susceptibility are also discussed.

gr-qc↗