arXiv subjects

H. C. Liu

Publications and source records attributed to H. C. Liu.

7 recordsLinked to original sources

arXiv2025

Towards Understanding the Origin of Swift Gamma-Ray Bursts Driven by Magnetars

We analyze a sample of\textit{ Swift} gamma-ray bursts (GRBs) with extended emissions in $γ$-rays and/or X-ray plateaus that may be driven by magnetars. Multi-wavelength data and multi-standards have been adopted to investigate the issue jointly. First, we find that GRBs with both extended emission and X-ray plateau satisfy a three-parameter relation between the luminosity and the end time of X-ray plateaus and the $γ$-ray isotropic energy as $L_X\varpropto T_a^{-1.13}E_{γ,iso}^{0.74}$, which is consistent with that of normal GRBs. Second, we distinguish these GRBs in the plane of magnetic field versus period of neutron star and find that almost all GRBs but GRB 211024B have reasonable periods and majority of them could be powered by magnetars. Third, we standardize the X-ray afterglows with distinct characteristics and find that the standard X-ray light curves with/without plateaus are significantly different. The standardized X-ray plateaus are similar to the mean temporal profile of magnetars. Fourth, it is verified with a K-S test that all types of GRBs except short ones have the similar distributions of redshift and isotropic energy in the observer/rest frame. GRBs with internal plateaus are significantly different from those of normal long GRBs and GRBs with external plateaus and/or extended emissions. Interestingly, the isotropic energy distributions of GRBs with internal and external plateaus are identical with those of short and long GRBs, respectively. Overall, our study can bring solid evidence that the fascinating magnetars could have multi-formation channels to account for not only short but also long GRBs with either internal or external X-ray plateaus as well.

astro-ph.HE↗

arXiv2025

Correlations between Event Rates of Short Gamma-Ray Bursts and Star Formation Rates with/without Time Delay

In this paper, we systematically investigate the redshift and luminosity distributions as well as the event rates of short Gamma-Ray Bursts (SGRBs) detected by Swift, Fermi, Konus-wind satellites. It is found that the distributions of redshift and luminosity of Fermi and Konus-wind SGRBs are identical and they obviously differ from those of Swift/BAT SGRBs. The luminosity distributions of SGRBs detected by diverse detectors can be uniformly fitted by a smoothly broken power-law function. The median luminosity of Swift SGRBs is about one order of magnitude smaller than that of Fermi/GBM or Konus-wind SGRBs. We also compare the local event rates of Swift/BAT, Fermi/GBM and Konus-wind SGRBs and find that the local rate of Swift SGRBs is around two orders of magnitude larger than that of either Fermi or Konus-wind SGRBs, while the latter two rates are comparable. The observed SGRB rates can be successfully fitted by a power-law plus Gauss function. The SGRB rates of three kinds of detectors matches the delayed/undelayed SFRs well except the delayed Lognormal and/or Gaussian SFRs at higher redshift and exceed all types of SFRs at lower redshift of $z<1$. After deducting the diverse SFR components from the SGRB rates, we surprisingly notice that the remaining SGRB rates steeply decline with redshift in a power-law-like form, indicating that these SGRBs could emerge from the old star populations or compact binary star mergers.

astro-ph.HE↗

arXiv2014

Large gap, a pseudogap and proximity effect in the Bi2Te3/Fe1+yTe interfacial superconductor

We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show a very large superconducting twin-gap structure with an energy scale exceeding that of bulk FeSe or FeSe1-xTex by a factor of 4. While the larger gap is isotropic and attributed to a thin FeTe layer in proximity of the interface, the smaller gap has a pronounced anisotropy and is associated with proximity-induced superconductivity in the topological insulator Bi2Te3. Zero resistance is lost above 8 K, but superconducting fluctuations are visible up to at least 12 K and the large gap is replaced by a pseudogap that persists up to 40 K. The spectra show a pronounced zero-bias conductance peak in the superconducting state, which may be a signature of an unconventional pairing mechanism.

cond-mat.supr-con↗

arXiv2012

A phonon scattering assisted injection and extraction based terahertz quantum cascade laser

A novel lasing scheme for terahertz quantum cascade lasers, based on consecutive phonon-photon-phonon emissions per module, is proposed and experimentally demonstrated. The charge transport of the proposed structure is modeled using a rate equation formalism. An optimization code based on a genetic algorithm was developed to find a four-well design in the $\mathrm{GaAs/Al_{0.25}Ga_{0.75}As}$ material system that maximizes the product of population inversion and oscillator strength at 150 K. The fabricated devices using Au double-metal waveguides show lasing at 3.2 THz up to 138 K. The electrical characteristics display no sign of differential resistance drop at lasing threshold, which suggests - thanks to the rate equation model - a slow depopulation rate of the lower lasing state, a hypothesis confirmed by non-equilibrium Green's function calculations.

cond-mat.mes-hall↗

arXiv2010

Bertrand's paradox: a physical solution

We present a conclusive answer to Bertrand's paradox, a long standing open issue in the basic physical interpretation of probability. The paradox deals with the existence of mutually inconsistent results when looking for the probability that a chord, drawn at random in a circle, is longer than the side of an inscribed equilateral triangle. We obtain a unique solution by substituting chord drawing with the throwing of a straw of finite length L on a circle of radius R, thus providing a satisfactory operative definition of the associated experiment. The obtained probability turns out to be a function of the ratio L/R, as intuitively expected.

physics.data-an↗

arXiv2009

Stable mode-locked pulses from mid-infrared semiconductor lasers

We report the unequivocal demonstration of mid-infrared mode-locked pulses from a semiconductor laser. The train of short pulses was generated by actively modulating the current and hence the optical gain in a small section of an edge-emitting quantum cascade laser (QCL). Pulses with pulse duration at full-width-at-half-maximum of about 3 ps and energy of 0.5 pJ were characterized using a second-order interferometric autocorrelation technique based on a nonlinear quantum well infrared photodetector. The mode-locking dynamics in the QCLs was modelled and simulated based on Maxwell-Bloch equations in an open two-level system. We anticipate our results to be a significant step toward a compact, electrically-pumped source generating ultrashort light pulses in the mid-infrared and terahertz spectral ranges.

physics.optics↗

arXiv1998

Negative capacitance effect in semiconductor devices

Nontrivial capacitance behavior, including a negative capacitance (NC) effect, observed in a variety of semiconductor devices, is discussed emphasizing the physical mechanism and the theoretical interpretation of experimental data. The correct interpretation of NC can be based on the analysis of the time-domain transient current in response to a small voltage step or impulse, involving a self-consistent treatment of all relevant physical effects (carrier transport, injection, recharging etc.). NC appears in the case of the non-monotonic or positive-valued behavior of the time-derivative of the transient current in response to a small voltage step. The time-domain transient current approach is illustrated by simulation results and experimental studies of quantum well infrared photodetectors (QWIPs). The NC effect in QWIPs has been predicted theoretically and confirmed experimentally. The huge NC phenomenon in QWIPs is due to the non-equilibrium transient injection from the emitter caused by the properties of the injection barrier and the inertia of the QW recharging.

cond-mat.mes-hall↗