arXiv subjects

H. B. Niu

Publications and source records attributed to H. B. Niu.

4 recordsLinked to original sources

arXiv2022

Group Theory Analysis of Phonons in Monolayer Chromium Trihalides and Their Janus Structures

A contrastive investigation of the symmetry aspects of phonons in monolayer chromium trihalides and their Janus structures Y$_3$-Cr$_2$-X$_3$ (X, Y = F, Cl, Br, I) by group theory is presented. We first classify all phonons at the Brillouin-zone center ($Γ$) into the irreducible representation. Then the infrared and Raman activity of optic phonons, Raman tensors, and the possible polarization assignments of R active phonons are predicted. Base on these results, we clarify the the discrepancy about the Raman activity o optic modes in monolayer CrI$_3$. Besides, we find that the Raman and infrared spectra for X$_3$-Cr$_2$-X$_3$ are exclusive, whereas that for Janus Y$_3$-Cr$_2$-X$_3$ are coincident. This distinction is vital for optic spectra identification of Janus Y$_3$-Cr$_2$-X$_3$ monolayer from X$_3$-Cr$_2$-X$_3$ monolayer. In addition, we derive the symmetry-matched phonon eigenfunctions and corresponding schematic representations of the eigenvectors for both F$_3$-Cr$_2$-I$_3$ and I$_3$-Cr$_2$-I$_3$ monolayer, which demonstrate intuitively the origin of phonon chirality and magnetism. At last, our analysis indicates that the spin-phonon coupling, the magneto-optical effect of infrared and Raman active phonons, and phonon chirality should be observed in Janus Y$_3$-Cr$_2$-X$_3$ monolayer as that and even easier than that in X$_3$-Cr$_2$-X$_3$ monolayer. Our work provides a detailed guiding map for experimental characterization of Y$_3$-Cr$_2$-X$_3$ monolayer, and also reveals important effects of optic phonons in Janus Y$_3$-Cr$_2$-X$_3$ monolayer.

cond-mat.mtrl-sci↗

arXiv2019

Precise determination of stellar parameters of the ZZ Ceti and DAZ white dwarf GD 133 through asteroseismology

An increasing number of white dwarf stars show atmospheric chemical composition polluted by heavy elements accreted from debris disk material. The existence of such debris disks strongly suggests the presence of one or more planet(s) whose gravitational interaction with rocky planetesimals is responsible for their disruption by tidal effect. The ZZ Ceti pulsator and polluted DAZ white dwarf GD 133 is a good candidate for searching for such a potential planet. We started in 2011 a photometric follow-up of its pulsations. As a result of this work in progress, we used the data gathered from 2011 to 2015 to make an asteroseismological analysis of GD 133, providing the star parameters from a best fit model with $M$/$M_{\odot}$ = 0.630 $\pm$ 0.002, $T_{\rm eff}$ = 12400 K $\pm$ 70 K, log($M_{\rm He}/M$) = -2.00 $\pm$ 0.02, log($M_{\rm H}/M$) = -4.50 $\pm$ 0.02 and determining a rotation period of $\approx$ 7 days.

astro-ph.SR↗

arXiv2012

PSR B0826-34: Sometimes a rotating radio transient

We report on the detection of sporadic, strong single pulses co-existing with a periodic weak emission in the duration of weak mode of PSR B0826-34. The intensities and durations of these pulses are comparable with that of the sub-pulses in the strong mode, and these pulses are distributed within the phase ranges of the main-pulse and interpulse of the strong-mode average profile. These results suggest that there are most possibly sporadic, very short timescale turn-on of strong-mode emission during the weak-mode state of the pulsar. The emission features of the bursts of strong pulses of PSR B0826-34 during its weak-mode state are similar to those of the rotating radio transients (RRATs). PSR B0826-34 is the second pulsar known which oscillates between pulsar-like and RRAT-like modes.

astro-ph.SR↗

arXiv2012

Radiation properties of extreme nulling pulsar J1502-5653

We report on radiation properties of extreme nulling pulsar J1502-5653, by analyzing the data acquired from the Parkes 64-m telescope at 1374 MHz. The radio emission from this pulsar exhibits sequences of several tens to several hundreds consecutive burst pulses, separated by null pulses, and the appearance of the emission seems quasi-periodic. The null fraction from the data is estimated to be 93.6%. No emission is detected in the integrated profile of all null pulses. Systematic modulations of pulse intensity and phase are found at the beginning of burst-pulse sequences just after null. The intensity usually rises to a maximum for the first few pulses, then declines exponentially afterwards, and becomes stable after few tens of pulse periods. The peak phase appears at later longitudes for the first pulse, then drifts to earlier longitudes rapidly, and then systematic drifting gradually vanishes while the intensity becomes stable. In this pulsar, the intensity variation and phase modulation of pulses are correlated in a short duration after the emission starts following a null. Observed properties of the pulsar are compared with other nulling pulsars published previously, and the possible explanation for phase modulation is discussed.

astro-ph.SR↗