arXiv subjects

Y. S. Wang

Publications and source records attributed to Y. S. Wang.

49 records · Page 3Linked to original sources

arXiv2019

Hot disk of the Swift J0243.6+6124 revealed by Insight-HXMT

We report on analysis of observations of the bright transient X-ray pulsar \src obtained during its 2017-2018 giant outburst with Insight-HXMT, \emph{NuSTAR}, and \textit{Swift} observatories. We focus on the discovery of a sharp state transition of the timing and spectral properties of the source at super-Eddington accretion rates, which we associate with the transition of the accretion disk to a radiation pressure dominated (RPD) state, the first ever directly observed for magnetized neutron star. This transition occurs at slightly higher luminosity compared to already reported transition of the source from sub- to super-critical accretion regime associate with onset of an accretion column. We argue that this scenario can only be realized for comparatively weakly magnetized neutron star, not dissimilar to other ultra-luminous X-ray pulsars (ULPs), which accrete at similar rates. Further evidence for this conclusion is provided by the non-detection of the transition to the propeller state in quiescence which strongly implies compact magnetosphere and thus rules out magnetar-like fields.

astro-ph.HE↗

arXiv2019

In-orbit demonstration of X-ray pulsar navigation with the Insight-HXMT satellite

In this work, we report the in-orbit demonstration of X-ray pulsar navigation with Insight-Hard X-ray Modulation Telescope (Insight-HXMT), which was launched on Jun. 15th, 2017. The new pulsar navigation method 'Significance Enhancement of Pulse-profile with Orbit-dynamics' (SEPO) is adopted to determine the orbit with observations of only one pulsar. In this test, the Crab pulsar is chosen and observed by Insight-HXMT from Aug. 31th to Sept. 5th in 2017. Using the 5-day-long observation data, the orbit of Insight-HXMT is determined successfully with the three telescopes onboard - High Energy X-ray Telescope (HE), Medium Energy X-ray Telescope (ME) and Low Energy X-ray Telescope (LE) - respectively. Combining all the data, the position and velocity of the Insight-HXMT are pinpointed to within 10 km (3 sigma) and 10 m/s (3 sigma), respectively.

astro-ph.IM↗

arXiv2018

Insight-HXMT observations of the New Black Hole Candidate MAXI J1535-571: timing analysis

We present the X-ray timing results of the new black hole candidate (BHC) MAXI J1535-571 during its 2017 outburst from Hard X-ray Modulation Telescope (\emph{Insight}-HXMT) observations taken from 2017 September 6 to 23. Following the definitions given by \citet{Belloni2010}, we find that the source exhibits state transitions from Low/Hard state (LHS) to Hard Intermediate state (HIMS) and eventually to Soft Intermediate state (SIMS). Quasi-periodic oscillations (QPOs) are found in the intermediate states, which suggest different types of QPOs. With the large effective area of \emph{Insight}-HXMT at high energies, we are able to present the energy dependence of the QPO amplitude and centroid frequency up to 100 keV which is rarely explored by previous satellites. We also find that the phase lag at the type-C QPOs centroid frequency is negative (soft lags) and strongly correlated with the centroid frequency. By assuming a geometrical origin of type-C QPOs, the source is consistent with being a high inclination system.

astro-ph.HE↗

arXiv2009

Deprojection technique for galaxy cluster considering point spread function

We present a new method for the analysis of Abell 1835 observed by XMM-Newton. The method is a combination of the Direct Demodulation technique and deprojection. We eliminate the effects of the point spread function (PSF) with the Direct Demodulation technique. We then use a traditional depro-jection technique to study the properties of Abell 1835. Compared to that of deprojection method only, the central electron density derived from this method increases by 30%, while the temperature profile is similar.

astro-ph.IM↗

arXiv2003

Superfluid response in monolayer high-Tc cuprates

We have studied the doping dependence of the in-plane and out-of-plane superfluid density, ρ^s(0), of two monolayer high-Tc superconductors, HgBa_2CuO_{4+δ} and La_{2-x}Sr_xCuO_4, using the low frequency ac-susceptibility and the muon spin relaxation techniques. For both superconductors, ρ^s(0) increases rapidly with doping in the under- and optimally doped regime and becomes nearly doping independent above a critical doping, p_c = 0.20.

cond-mat.supr-con↗

arXiv2001

Possible superconductivity above 400 K in carbon-based multiwall nanotubes

Magnetization and resistance measurements were carried out on carbon-based multiwall nanotubes. Both magnetization and resistance data can be consistently explained in terms of bulk superconductivity above 400 K although we cannot completely rule out other possible explanations to the data.

cond-mat.supr-con↗

arXiv2001

Correlation between the residual resistance ratio and magnetoresistance in MgB2

The resistivity and magnetoresistance in the normal state for bulk and thin-film MgB2 with different nominal compositions have been studied systematically. These samples show different temperature dependences of normal state resistivity and residual resistance ratios although their superconducting transition temperatures are nearly the same, except for the thin-film sample. The correlation between the residual resistance ratio (RRR) and the power law dependence of the low temperature resistivity, rho vs. T^c, indicates that the electron-phonon interaction is important. It is found that the magnetoresistance (MR) in the normal state scales well with the RRR, a0(MR) proportional to (RRR)^2.2 +/- 0.1 at 50 K. This accounts for the large difference in magnetoresistance reported by various groups, due to different defect scatterings in the samples.

cond-mat.supr-con↗

arXiv2001

Direct Observation of Coexistence of Ferromagnetism and Superconductivity in RuSr2(Gd0.7Ce0.3)2Cu2O10

Recent reports of the detecting of ferromagnetism and superconductivity in ruthenium-cuprates have aroused great interest. Unfortunately, whether the two antagonistic phenomena coexist in the same space in the compounds remains unresolved. By employing the magneto-optical-imaging technique, ferromagnetism and superconductivity were indeed directly observed to coexist in the same space in RuSr2(Gd0.7Ce0.3)2Cu2O10 within the experimental resolution of ~ 10 (mu)m. The observation sets a length scale limit for models proposed to account for the competition between ferromagnetism and superconductivity, especially d-wave superconductivity, in this interesting class of compounds.

cond-mat.supr-con↗

arXiv2000

Evidence for novel polaronic Fermi-liquid in doped oxides

The modern multi-polaron theory predicts a polaronic Fermi-liquid state, but such a state has not been unambigously confirmed by experiment so far. Here we report theoretical and experimental studies of the isotope effects on the low temperature kinetic properties of the doped ferromagnetic manganites. Our results provide clear evidence for a novel polaronic Fermi-liquid state in doped oxides.

cond-mat.mtrl-sci↗

arXiv2000

Evidence for the immobile bipolaron formation in the paramagnetic state of the magnetoresistive manganites

Recent research suggests that the charge carriers in the paramagnetic state of the magnetoresistive manganites are small polarons. Here we report studies of the oxygen-isotope effects on the intrinsic resistivity and thermoelectric power in several ferromagnetic manganites. The precise measurements of these isotope effects allow us to make a quantitative data analysis. Our results do not support a simple small-polaron model, but rather provide compelling evidence for the presence of small immobile bipolarons, i.e., pairs of small polarons. Since the bipolarons in the manganites are immobile, the present result alone appears not to give a positive support to the bipolaronic superconductivity theory for the copper-based perovskites.

cond-mat.str-el↗

arXiv1999

Absence of a Bulk Meissner State in RuSr2GdCu2O8

We have systematically investigated the magnetic, electrical, and structural properties of RuSr2GdCu2O8, in which a long-range ferromagnetic order and superconductivity have been previously reported to coexist. Based on the reversible magnetization results, we conclude that the bulk Meissner state does not exist in this compound and that the condensation energy associated with superconductivity is negligible. The absence of a bulk Meissner state and the superconductivity detected are thus attributed to the possible appearance of a sponge-like crypto-superconducting fine structure in RuSr2GdCu2O8 samples that are found to be chemically homogeneous to 1-2 mu m and electrically uniform to \~ 10 mu m across the sample.

cond-mat.supr-con↗

arXiv1999

c-Axis Superfluid Response and Pseudogap in High-Tc Superconductors

To gain insight into the out-of-plane electrodynamics of high-$T_c$ superconduct ors we have measured the absolute values and temperature dependence of the c-a xis magnetic penetration depth $λ_c(T)$ for two typical single layer high -$T_c$ cuprates, La$_{2-x}$Sr$_x$CuO$_4$ and HgBa$_2$CuO$_{4+x}$ as a function o f doping. A distinct change in the behaviour of $λ_c$ is observed near 0. 20 holes/Cu, which is related to the opening of the normal state pseudogap. The variation of $λ_c$ with doping is qualitatively similar to that of the in -plane component, $λ_{ab}$, which suggests that the c-axis superfluid r esponse is mainly governed by the superconducting condensation energy. The stron g doping dependence of $λ_c(0)$ for p<0.20 provides an explanation for the discrepancies in the literature.

cond-mat.supr-con↗

arXiv1999

Effects of carrier concentration on the superfluid density of high-T_c cuprates

The absolute values and temperature, T, dependence of the in-plane magnetic penetration depth, $λ_{ab}$, of La_{2-x}Sr_xCuO_4 and HgBa_2CuO_{4+δ} have been measured as a function of carrier concentration. We find that the superfluid density, $ρ_s$, changes substantially and systematically with doping. The values of $ρ_{s}(0)$ are closely linked to the available low energy spectral weight as determined by the electronic entropy just above T_c and the initial slope of $ρ_{s}(T)/ρ_{s}(0)$ increases rapidly with carrier concentration. The results are discussed in the context of a possible relationship between $ρ_s$ and the normal-state (or pseudo) energy gap.

cond-mat.supr-con↗